4 inch Apo VS 6 inch F-8 Newt
stevew
be a great combination of portability and performance. There are very
popular models from TV, AP,TMB, and Vixen to name a few. However I have
never been able to bring myself to buy one. I just can't see any of them
being better than a 6 inch F-8 Newt. So what is it about the apos that would
make someone spend $3000 when a 6 inch F-8 can be purchased for $300?
Just curious.
Steve
Orion
apples to oranges.
A 4" APO is a completely different animal than a 6" newt, which, btw, is
technically a APO also.
The best you can come up with is rough approximations.
Cleardarkskies!
Orion
"stevew" <ste...@intergate.bc.ca> wrote in message
news:vac7r78...@corp.supernews.com...
---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.467 / Virus Database: 266 - Release Date: 4/2/2003
Roger Hamlett
"Orion" <mark....@syntegra.com> wrote in message
news:N%ppa.360$dj1....@news7.onvoy.net...
> I think the heart of your dilemma is to make the common mistake of
comparing
> apples to oranges.
> A 4" APO is a completely different animal than a 6" newt, which, btw, is
> technically a APO also.
my mind meet the definition of an apochromat, or an achromat. These terms
are surely reserved for lens combinations, which correct chromatic
aberrations, producing either two corrected points across the visible
spectrum, or three. A reflector has no aberrated frequencies (in this
regard) at all. It gives similar spectral behaviour to an apochromat, but
the word doen't really apply...
> The best you can come up with is rough approximations.
> Cleardarkskies!
> Orion
> "stevew" <ste...@intergate.bc.ca> wrote in message
> news:vac7r78...@corp.supernews.com...
> > I have always wanted a beautiful 4 inch Apo, I am not sure why, they
seem
> to
> > be a great combination of portability and performance. There are very
> > popular models from TV, AP,TMB, and Vixen to name a few. However I have
> > never been able to bring myself to buy one. I just can't see any of them
> > being better than a 6 inch F-8 Newt. So what is it about the apos that
> would
> > make someone spend $3000 when a 6 inch F-8 can be purchased for $300?
> > Just curious.
> > Steve
Each displays their own sets of aberrations. For wide field views, a
Newtonian, will have massive coma. The Newtonian will show diffraction from
both the central obstruction, and the spider. The APO, will still display
some residual chromatic aberration. Generally mirrors produce some scatter,
and more losses than a lens surface if properly multi-coated. Where the
properly designed APO really 'wins', is for a large corrected field. Nothing
is probably better as a photographic platform, or for use with a lens with a
big field stop. The lack of scattered light in the tube (combined with the
lack of extra diffraction effects), produces some of the best views around.
However the cost is like comparing a Ford with a Ferrari. At the end of the
day, the latter costs ten times as much, but on some measures may be no
better or even worse than the former...
Best Wishes
Tony Flanders
> I just can't see any [4-inch APO] being better than a
> 6 inch F-8 Newt. So what is it about the apos that would
> make someone spend $3000 when a 6 inch F-8 can be purchased
> for $300?
A 4-inch APO has several clear objective advantages:
* A 4-inch APO is far better for wide-field astrophotography.
* A 4-inch APO is much more portable, especially when the mount
is taken into consideration.
* A 4-inch APO reaches thermal equilibrium much faster.
* A 4-inch APO delivers a much wider maximum field of view.
And then, of course, there are all the purely subjective reasons
including (as you hint) the urge to spend large quantities of
money on neat toys. And on top of that, the 4-inch APO is not
far behind the 6" Newt in optical performance in any category.
And for somebody who is truly devoted to the hobby, $3K is not
a huge sum of money. After all, professional photographers
(terrestrial) spend more than that on film every year.
- Tony Flanders
andrea tasselli
I can't see them being better than a 6" f/6 newton or even f/5 either,
although in the latter case coma starts to become annoying to say the
least. With the possible exception of large format chemical
astrophotography there's nothing one cannot do with a newt than can be
done with an expensive APO. And with 2" advantage (over the 4" APO)
there's no possible comparison in both planetary and deep sky work.
This however will never prevent people spending their money on fancy
cute little scopes.
Andrea T.
My Astronomy Pages at:
http://www.geocities.com/andreatax/index.htm
Jon Isaacs
>
> * A 4-inch APO is far better for wide-field astrophotography.
> * A 4-inch APO is much more portable, especially when the mount
> is taken into consideration.
> * A 4-inch APO reaches thermal equilibrium much faster.
> * A 4-inch APO delivers a much wider maximum field of view.
>
* A 4 inch APO does not need frequent collimation for optimal results.
jon isaacs
Rockett Crawford
My opinion is that for visual of deep sky objects the more aperture the
better. I have a 4 inch APO, but if I was going to hunt faint fuzzies,
I would take my 8 inch Newtonian or my 8 or 11 inch SCT. For wide
field viewing the APO is hard to beat, especially in the faster f/ratios.
I would go for the 8 inch over the 6 inch because it costs just a little
more but is almost twice the aperture in mirror area. As far as portability
I have an f/6 8 inch Newtonian that I built in the 80s on a small Dob mount
and it's about as portable as anyone would want short of trying to carry
a scope on an airplane. It's tube breaks down into two and it will fit
in any trunk. When it's assembled, you just pick it up and go, tube in
one hand (handle) and dob base in the other and run outside, plonk
it down on the ground and start observing. Collimation and cooldown
are factors, but if critical observing is required, collimation takes just
a minute and the scope cools down pretty rapidly while checking out
the moons of Jupiter or the phases of Venus.
For planets, an 8 inch would still be better. For film and CCD imaging,
the APO would be the way to go unless the 8 inch newt has an
excellent mirror like a Zambuto or Pegasus and is on a good mount.
Then it would be a matter of wide field vrs detail.
My 2 cents,
Rockett Crawford
--
Capella's Observatory
http://web2.airmail.net/capella
Rockett Crawford
Siegfried Gonzi
> My opinion is that for visual of deep sky objects the more aperture the
> better. I have a 4 inch APO, but if I was going to hunt faint fuzzies,
> I would take my 8 inch Newtonian or my 8 or 11 inch SCT.
Hi:
You may not forget:
The apo has the following advantages:
(define (fuck-the-shit apo-lunatics)
(let loop-over-lunatics ((lunatics-list apo-lunatics))
(if (lunatics-list-will-ever-stop? lunatics-list)
#f
(begin
(print "Apo has zero cool-down time")
(print "Apo needs no re-collimation")
(print "Apo has zero obstruction")
(print "Apo has better color correction")
(print "Apo gives sharper images")
(print "Apo is close to the daw-limit")
(print "Apo has 360 degree of field")
(print "Apo is easier to haul around")
(print "Apo has zero coma")
(print "Apo is more joy")
(print "Apo is better for scrutinizing the
blue halo aroundthe moon")
(print "Apo is built by dedicated lens makers")
(print "Apo is simply better for the serious amateur")
(print "It will stop raining after placing out the apo")
(loop-over-lunatics (cdr lunatics-list))))))
> I would go for the 8 inch over the 6 inch because it costs just a little
> more but is almost twice the aperture in mirror area. As far as portability
> I have an f/6 8 inch Newtonian that I built in the 80s on a small Dob mount
> and it's about as portable as anyone would want short of trying to carry
> a scope on an airplane. It's tube breaks down into two and it will fit
> in any trunk. When it's assembled, you just pick it up and go, tube in
> one hand (handle) and dob base in the other and run outside, plonk
> it down on the ground and start observing. Collimation and cooldown
> are factors, but if critical observing is required, collimation takes just
> a minute and the scope cools down pretty rapidly while checking out
> the moons of Jupiter or the phases of Venus.
Give up: the lunatics already made their mind.
S. Gonzi
ERIC K. CHEU
The biggest reason, of course, being convenience. Which is why people would
shell out large amounts of cash. Take your pick - do you want to spend more time,
effort and energy to get what you want, or do you want to spend more money (a
new requires more of the latter, while an apo refractor requires the latter).
Jon Isaacs
>Hi:
>
>You may not forget:
>
>The apo has the following advantages:
>
>(define (fuck-the-shit apo-lunatics)
Some thoughts for you Sigfried:
The rest of us here try to act like gentlemen. Thus what happens is that most
of the time we just let your "rude and crude" remarks slide by along with
anything else you might have to say.
Your delivery truly detracts from anything you might want to say or learn.
I think you might actually have something worth saying at times but it is not
obvious.
I would like to ask you to quit using foul language and show some respect for
the rest of the people who post here.
If you want your thoughts and opinions to be respected, then you need to show
the same respect to others who have differing ideas than you might.
Jon Isaacs
Jan Owen
--
To reply, remove the "z" if one appears in my address
"Jon Isaacs" <joni...@aol.com> wrote in message
news:20030423125208...@mb-m29.aol.com...
Pasushkopa
Tom Trusock
<rcra...@audiotel.com> wrote:
Well put Rockett -
Just another datapoint:
I currently have a nice 4" apo, and a fine 10" newt. The 4" APO sees
far more light simply because it's a better grab and go scope for all
the reasons every one has already covered.
Not for one second would I ever say that I can see anywhere near as
much with the apo as with the 10" newt. No matter how you cut it - 4"
is 4" is 4".
As to price - well, I have about the same wrapped up in both, so I
don't really buy the $300 to $3000 arguement.
YMMV of course, but I figure I've gotten my monies worth outta the
apo, and would do it again.
Tom T.
Stephen Paul
To spend that much money on a reflector, you'd have to trade portability for
aperture. <g>
Kidding aside, I recommend that you go look through one, and draw your own
conclusion. Like it or not, high end refractors are sweet to those with the
appetite and the necessary financial resources.
One can also question why a man commutes in an SUV with full leather
upholstery and power everything, when a less extravagant and more efficient
automobile will take him just as far. Or, why someone would purchase 2500 sq
ft of living space in town, when the same space a commute away costs several
10's of thousands less (in US dollars).
Convenience?
Extravagance?
Quality of craftsmanship?
Location?
Satisfaction?
Financial wealth?
I strongly believe that anyone who asks the question, simply hasn't had the
opportunity to do a side by side comparison. The conclusion drawn, is
completely up to the individual. Until you have drawn your own conclusion,
the question will always haunt you.
This isn't about anyone else. It's about you. Why would you be better off or
worse off with an apo? No one can tell you that. You have to see for
yourself. I've observed through a 4" F5.8 TV-101, and it is an awesome
performer for it's aperture, both at high power, and at low power/wide
field.
Would I buy one today? Not for visual astronomy alone. Like you, I can't
justify the cost. Will I buy one in the future? Who knows? Would I _like_ to
buy one... you bet. I'd like to have one of everything. <g>
-Stephen Paul
Joseph O'Neil
wrote:
Imaging - film or CCD - an APO would be better. In that
sense, $3,000 is nto a lot of money. Just look up the prices of
premium camera optics, and you'll see what I mean.
Also bear in mind that, IMO, a $300 newt will nto be as good -
optical quality speaking - as an $3,000 APO. A really good mirror
set might cost you $300 alone just for the optics.
By the time youadd good mechanics - a good tube, good mirror
cell, good focuser - for example, a good JMI or Burgess Focuser - will
set you back another $300 to $400 alone. Remember that most 4" APOs
will have focusers that, by themselves, would cost anywhere from $300
to $500.
Visually these focusers are wonderful to use, but not
essential. For imaging however, film or CCD, these focusers are
pretty much essential for fine, critical focus.
So if you compare *mechanical* quality, and make sure the
mechanical quality is equal, and then make sure the optical quality is
equal, that 6 inch newt might cost you around $1,000.
Still, for visual use, IMO, nothing beats a 6" or 8" or 10"
dob, especially when you compare bang for the buck.
Finally the REAL answer to your question - None of the above.
Everybody knows the real answer is a 6" mak-Newt beast the ass off
both.
(big evil grin :)
joe
Alan French
I disagree with this one. My wife's 4" Traveler on an AP 400 equatorial
mount and my RV-6 seem to be about on par in terms of portability, and our
6" f/8 Dob Newt would be about as portable as the Traveler on an altazimuth
mount.
"Tony Flanders" <tony_f...@yahoo.com> wrote in message
> [SNIP]
> * A 4-inch APO is much more portable, especially when the mount
> is taken into consideration.
> [SNIP]
To me, the big advantages of the 4" APO are its ability to provide low
power, wide fields of view that are unobtainable with a 6" f/8 Newt, the
fact that the OTA fits in legal carry-on luggage, and that it can double as
a nice nature scope (although I lean toward a smaller APO for this).
Clear skies, Alan
Jose Suro
it bad enough. Just having gone through the gamut picking a new telescope, I
thought long and hard about "the best" 4 inch scope with all the trimmings.
In the end, I settled for a computerized 11" SCT. Why you ask? The only
thing the 4 inch scope would be better at would be letting me say "I've got
the best 4" scope in the world", and not caring much on saying things like
that, I decided to concentrate more on what I could see and do, than on what
I could say. And if anybody mentions wide field, my fuji binocs will do that
just fine - and they are only 30mm smaller than the 4", and furthermore,
most of my observing is done at over 150x.
Take Care,
JAS
Jeff Cook
> In the end, I settled for a computerized 11" SCT. Why you ask? The
only
> thing the 4 inch scope would be better at would be letting me say
"I've got
> the best 4" scope in the world", and not caring much on saying things
like
C11s have suddenly become portable? No need to overstate for the sake of
it.
Joe Bergeron
<ste...@intergate.bc.ca> wrote:
Maybe the fact that the refractor isn't 4 feet long?
--
Joe Bergeron
Jose Suro
too :).
Take Care,
JAS
"Jeff Cook" <je...@cookstudios.com> wrote in message
news:3ea74...@vienna7.his.com...
andrea tasselli
> On Tue, 22 Apr 2003 22:06:16 -0700, "stevew" <ste...@intergate.bc.ca>
> wrote:
>
> >I have always wanted a beautiful 4 inch Apo, I am not sure why, they seem to
> >be a great combination of portability and performance. There are very
> >popular models from TV, AP,TMB, and Vixen to name a few. However I have
> >never been able to bring myself to buy one. I just can't see any of them
> >being better than a 6 inch F-8 Newt. So what is it about the apos that would
> >make someone spend $3000 when a 6 inch F-8 can be purchased for $300?
>
> Imaging - film or CCD - an APO would be better. In that
> sense, $3,000 is nto a lot of money. Just look up the prices of
> premium camera optics, and you'll see what I mean.
For film maybe but not really sure once you add a coma corrector (have
you ever seen images taken with a Vixen SS200?) and for CCD not at at
all.
>
> Also bear in mind that, IMO, a $300 newt will nto be as good -
> optical quality speaking - as an $3,000 APO. A really good mirror
> set might cost you $300 alone just for the optics.
>
> By the time youadd good mechanics - a good tube, good mirror
> cell, good focuser - for example, a good JMI or Burgess Focuser - will
> set you back another $300 to $400 alone. Remember that most 4" APOs
> will have focusers that, by themselves, would cost anywhere from $300
> to $500.
> Visually these focusers are wonderful to use, but not
> essential. For imaging however, film or CCD, these focusers are
> pretty much essential for fine, critical focus.
Hogwash. You don't need these $$$$ focusers to do that. You can get
away with decent rack and pinion or normal crayford and still do a
more than a decent job.
>
> So if you compare *mechanical* quality, and make sure the
> mechanical quality is equal, and then make sure the optical quality is
> equal, that 6 inch newt might cost you around $1,000.
>
> Still, for visual use, IMO, nothing beats a 6" or 8" or 10"
> dob, especially when you compare bang for the buck.
>
> Finally the REAL answer to your question - None of the above.
> Everybody knows the real answer is a 6" mak-Newt beast the ass off
> both.
Well, we know that ;-)
Rich McMahon
Steve
As far as the apo its extremely portable, gives good wide field views
and is sealed from allot of contamination that the newt would see.
Also no need to check collimation each time you use the scope. Most
high end apos are well made mechanically. Its also a neat scope to
own.
Optically there is no advantage to go with the apo other than a wider
field of view. A 6" newt will beat a 4" apo any day with the following
conditions; a well made mirror, good thermal mgmt and collimation.
For the best bang for the buck the newt is the clear winner.
Rich
On Tue, 22 Apr 2003 22:06:16 -0700, "stevew" <ste...@intergate.bc.ca>
wrote:
>I have always wanted a beautiful 4 inch Apo, I am not sure why, they seem to
Joseph O'Neil
>Hogwash. You don't need these $$$$ focusers to do that. You can get
>away with decent rack and pinion or normal crayford and still do a
>more than a decent job.
Well i'll disagree with you here. I have used both, and going
form a regular rach & pinion focuser to a high quality focuser with
fine focus control is a HUGE difference.
yes, you can make a standard rack & pinion work, but IMO, it's
like saying you can stick a V6 in a one ton pickup truck and still use
it for towing and hauling stuff around on a farm or construction site,
when a V8 will do the job a lot better, and when a V10 Cummings diesel
will do it even easier still.
When you catually use both and caompare the two how they work
in the real world, the extra money is very readily worth it.
anytime
joe
Jon Isaacs
>field of view. A 6" newt will beat a 4" apo any day with the following
>conditions; a well made mirror, good thermal mgmt and collimation.
The diffraction spikes of the spiders the diffraction effects of the diagonal
are issues with the newtonian. While there are newts with no spiders, these
are not of the $300 variety.
There are other issues with a $300 Newtonian like light bafflings etc that also
can degrade the image.
Over the years, there have been many side by side comparisions of a variety of
scopes, not sure I have seen one of an APO vs. a simple $300 six inch newtonian
but my guess would be that on planetary detail and on splitting double stars
that the APO would be superior.
This is not to say that a 6 inch Newtonian that was built with a good attention
to detail, could not be superior, just rather as I believe Joe O'neil said, it
would cost a $1000 or so.
And as someone else pointed out, the real comparison ought to be a 8 inch F6
Newt because the OTA is only slightly less portable and slightly more expensive
but the performance gain is substantial.
jon isaacs
Rockett Crawford
One of the nice things about a Newtonian is that you can
upgrade the focuser pretty easily if need be.
I bought a Starlight instruments focuser for my Mak-Newt and
it comes with a really nice, smooth fine focus.
take care,
Rockett
--
Capella's Observatory
http://web2.airmail.net/capella
"Joseph O'Neil" <jon...@multiboard.com> wrote in message
news:3ea7cb7...@news.multiboard.com...
Rockett Crawford
One of the nice things about a newtonian is that you can
upgrade the focuser pretty easily if need be.
I bought a Starlight instruments focuser for my Mak-Newt and
it comes with a really nice, smooth fine focus.
take care,
Rockett
--
Capella's Observatory
http://web2.airmail.net/capella
"Joseph O'Neil" <jon...@multiboard.com> wrote in message
news:3ea7cb7...@news.multiboard.com...
>
andrea tasselli
I see you have a vested interest in selling astrogear ->
isn't it?
I've used several chinese scopes and few had quite useable rack and
pinion focusers. Same applies to my russian crayfords (the ones on my
maks/MNs). Of course a very fine focuser would do the work better and
easier (much more of the latter though) but that's not to say that you
*need* one to achieve whatever goal provided that the one you have
meets a minimum number of criteria.
Jon Isaacs
>I see you have a vested interest in selling astrogear ->
>
>http://www.oneilphoto.on.ca
>
>isn't it?
Cheap shot and uncalled for.
>
>I've used several chinese scopes and few had quite useable rack and
>pinion focusers.
I have had a few of these myself and with some work, they are passable, but
they ain't great by any means, as they come they are prone to wobble, big
shifts and when they are adjusted to be sufficiently tight, they be prone to
stiffening up with colder weather.
They are never consistent like the RCF or Televue focusers I have and for a
novice like me, having a quality focuser makes the touchy job of focusing a CCD
camera significantly easier.
What I cannot figure out is why the focusers on the chinese refractors are so
marginal but the DOB focusers (teflon lined) are some smooth and even.
Jon Isaacs
Sean Golden
"stevew" <ste...@intergate.bc.ca> wrote:
> I have always wanted a beautiful 4 inch Apo, I am not sure why, they seem to
> be a great combination of portability and performance. There are very
> popular models from TV, AP,TMB, and Vixen to name a few. However I have
> never been able to bring myself to buy one. I just can't see any of them
> being better than a 6 inch F-8 Newt. So what is it about the apos that would
> make someone spend $3000 when a 6 inch F-8 can be purchased for $300?
> Just curious.
> Steve
>
>
Steve:
I am one of those who has spent almost $3K for a small apo refractor, so
I can at least give you my reasons for doing so.
I made an 8" dobsonian for a very reasonable cost, about $400. I enjoy
it immensely and use it a lot (although not much lately, we have had an
amazing amount of cloud cover lately).
But as much as I love the dob, I have never been able to get
consistently perfect views through it. I have to collimate it
frequently (well, about once a month) and it is big and bulky. It
suffers from long cool-down periods and thermal currents that I have
only been able to mitigate, never entirely solve. It is not difficult
to track things, but it sometimes gets annoying, especially when I want
my wife or kids to see what I am looking at.
Several years ago I purchased a Televue Pronto. I was amazed by the
images I saw through it, but was disturbed by the fringing it showed. I
upgraded to a TV Genesis and again was mesmerized by the perfect images,
but still wasn't completely happy with the color correction. So I again
upgraded to a TV-101, and then finally I discovered a telescope that
nearly satisfied my expectations for its aperture. But it was just a
bit too big for my needs, so I now have an AP Stowaway, which I now
believe to be nearly the perfect scope for my refractor needs.
Here is a single example of a comparison of experience between the dob
and the apo. Looking at M42 my dob shows an amazing amount of faint
detail, but the stars are never perfect balls of fire. In the Stowaway
the Trapezium is an amazing site, little perfect balls of fire floating
in space. Same with Albireo, or other double stars. For planetary
viewing, up to the limits of the aperture, the views are incredibly
sharp and clear, with absolutely *no* sudden thermal currents to degrade
the image. The only limits are the aperture and the atmosphere.
I know, intellectually, that I get more detail and brighter views in the
dob, and that is what I use for faint fuzzy hunting and most of my
"serious" visual observing. But even though I can't see as much in the
Stowaway, what I CAN see is so close to perfection that every time I use
it, I fall in love with it all over again. And I *never* have to
collimate it or wait more than a few minutes for it to cool down.
If I expected it to be a light bucket, I would be disappointed, but that
isn't what I expect. I expect it to perform as near to perfectly as a
92mm aperture will perform, and that is what it does. To me that is
worth the money. In fact I don't even think about the money I spent, I
figure if I ever want to sell it, I'll get that back. I am pretty sure
my dob wouldn't sell for more than a hundred bucks or so, it is quite
ugly.
There are also the issues of tracking, computer goto and imaging as well
as terrestrial and solar use, in which the Stowaway is vastly more
convenient to use when compared to my dob, but those are bonuses, not
the primary reason I love the little apo.
-sdg
Joseph O'Neil
wrote:
>I see you have a vested interest in selling astrogear ->
>http://www.oneilphoto.on.ca
>isn't it?
Well, that's a little like saying the Pope has a vesting
interest in beig religious - well DUH! Of course I'm interest! :)
Still, the focuers we make ourselves here are for *visual*
use, not imaging. My point has been better focusres for *imaging*.
For the record, I do not sell JMI, Fethertouch, etc, but i
have used them before, and i have to say,t heya re all excellent.
when you are out in the feild, trying to get a fine focus,
trust me, the better the focuser, the easier it is to get good
results.
joe
Rich McMahon
I agree with 300.00 it would be hard to get optics that would equal a
apo. Just the cost of getting an outstanding mirror would raise the
price of the pimary above 300.00 not to mention a good secondary,
quality spider and focuser.. So I think the 1k range is more
realistic. As far as diffraction spikes from the secondary dgm optics
has the off axis newt which has gotten very good reviews. But the
price of the scope is well over 1k.. A good review of this scope is at
www.scopereviews.com
Anyway I guess the point really is to get outstanding optics either
using lens or mirrors or a combination of both it costs. My meade 8
and 16 inch mirrors that I use at home are very good but theres better
out there but with a cost of much more money..
Rich
Other options which Ive heard really good results from are the
andrea tasselli
> atasselli wrote:
>
> >I see you have a vested interest in selling astrogear ->
> >
> >http://www.oneilphoto.on.ca
> >
> >isn't it?
>
> Cheap shot and uncalled for.
Are you Joe? No? Uncalled for comment -> noise.
>
> >
> >I've used several chinese scopes and few had quite useable rack and
> >pinion focusers.
>
> I have had a few of these myself and with some work, they are passable, but
> they ain't great by any means, as they come they are prone to wobble, big
> shifts and when they are adjusted to be sufficiently tight, they be prone to
> stiffening up with colder weather.
More specifically, Orion's Europas rack and pinion focusers. All of
the right out of the box fine for focusing on a f/5 scope. Don't know
about chinese refractors as I would touch 'em with a 10 yard stick.
>
> They are never consistent like the RCF or Televue focusers I have and for a
> novice like me, having a quality focuser makes the touchy job of focusing a CCD
> camera significantly easier.
Never try harder, eh?
>
> What I cannot figure out is why the focusers on the chinese refractors are so
> marginal but the DOB focusers (teflon lined) are some smooth and even.
Teflon is godsend for smooth action.
andrea tasselli
> On 24 Apr 2003 10:28:19 -0700, atas...@hotmail.com (andrea tasselli)
> wrote:
>
>
> >I see you have a vested interest in selling astrogear ->
> >http://www.oneilphoto.on.ca
> >isn't it?
>
> Well, that's a little like saying the Pope has a vesting
> interest in beig religious - well DUH! Of course I'm interest! :)
OK. So telling people that they need expensive focusers regardless of
whether the current ones are OK for the job is good for your business.
>
> Still, the focuers we make ourselves here are for *visual*
> use, not imaging. My point has been better focusres for *imaging*.
Better focusers are better focusers.
>
> For the record, I do not sell JMI, Fethertouch, etc, but i
> have used them before, and i have to say,t heya re all excellent.
I never said they weren't.
> when you are out in the feild, trying to get a fine focus,
> trust me, the better the focuser, the easier it is to get good
> results.
Not if the stock ones are of a decent make. In other words while it
might be nicer to have a FeatherTouch or similar (it also looks better
which is one of the selling points) it not *required* as your original
post implied.
Jon Isaacs
>
I am not Joe but you need to address what he says, not make implications that
he is interested in trying to sell focusers.
Cheap shot and an uncalled for.
>More specifically, Orion's Europas rack and pinion focusers. All of
>the right out of the box fine for focusing on a f/5 scope. Don't know
>about chinese refractors as I would touch 'em with a 10 yard stick.
Then I guess you didn't understand what sort of focusers Joe was talking about.
>> They are never consistent like the RCF or Televue focusers I have and for a
>> novice like me, having a quality focuser makes the touchy job of focusing a
>CCD
>> camera significantly easier.
>
>Never try harder, eh?
No reason to make it harder than it already is. But I imagine were you to
experience a stock Synta focuser you might well change your opinion. Marginal
for astrophotography.
>Teflon is godsend for smooth action.
>
>Andrea T.
But why the reflectors have such fine focusers and the refractors such poor
ones, that is what confuses me.
Jon Isaacs
Jon Isaacs
>whether the current ones are OK for the job is good for your business.
Remember the context of this discussion and the context of Joe's statement.
Context: the mechanical quality of a $300 Newtonian.
This is what Joe wrote:
"Also bear in mind that, IMO, a $300 newt will nto be as good -
optical quality speaking - as an $3,000 APO. A really good mirror
set might cost you $300 alone just for the optics.
By the time youadd good mechanics - a good tube, good mirror
cell, good focuser - for example, a good JMI or Burgess Focuser - will
set you back another $300 to $400 alone. Remember that most 4" APOs
will have focusers that, by themselves, would cost anywhere from $300
to $500.
Visually these focusers are wonderful to use, but not
essential. For imaging however, film or CCD, these focusers are
pretty much essential for fine, critical focus."
Joe is not trying to sell anything here, rather he is just pointing out that
the focuser, the cell, the tube are all important parts of the system, it takes
more than just a decent mirror.
Personally I think it is important to be reasonable with people who are part of
the industry who choose to post here. They can provide valuable experience and
see a lot more telescopes of a wider range than the rest of us, their thoughts
and input are valuable, whether it is Roland Christen or Joe O'neil.
So, rather than suggest that Joe has a vested interest, just address the facts.
Yes, there focusers on $300 DOBs are not too bad visually, some of them are
quite decent. But the context is comparing the performance of a $300 Newt to
that of a $300 APO and a big part of that difference is in the mechanical
components.
Jon Isaacs
Tony Flanders
> A 4-inch APO is much more portable [than a 6" F/8 Newt], especially
> when the mount is taken into consideration.
"Alan French" responded:
> I disagree with this one. My wife's 4" Traveler on an AP 400 equatorial
> mount and my RV-6 seem to be about on par in terms of portability, and our
> 6" f/8 Dob Newt would be about as portable as the Traveler on an altazimuth
> mount.
Hmm, I was wondering about my assertion after posting it. It is true
that, assuming identical tube sizes, a Newt is much more portable
than a refractor, because the EP is at the top rather than the
bottom, allowing a much shorter tripod to be used. The extreme
along these lines is the Dob mount, which disposes of the tripod
altogether.
It is also true that German Equatorial Mounts of APO-compatible
quality tend to be overbuilt for a 4" APO, and are usually quite
capable of handling a 6" F/8 Newt.
Even so, I stand by my assertion. A 6" F/8 Dob weighs about 50%
more than a 4" APO on a good alt-az mount, and occupies vastly
more volume. Now, for your particular uses, that difference
may be irrelevant. If you store your Dob at ground level and
always transport it by car, and the car is big enough to fit
the scope with the usual passengers and luggage, then the scope
is portable enough, and extra portability wouldn't help.
But I bet that if you bought an erecting prism for the Dob and
tried to use it for birding, you would notice the difference
in portability in a hurry!
For me, that fact that the OTA of a 4" APO fits easily in a
backpack is an overwhelming benefit in portability. I bet
you would see my point if you lived in a third-floor walkup!
- Tony Flanders
andrea tasselli
> >Optically there is no advantage to go with the apo other than a wider
> >field of view. A 6" newt will beat a 4" apo any day with the following
> >conditions; a well made mirror, good thermal mgmt and collimation.
>
> The diffraction spikes of the spiders the diffraction effects of the diagonal
> are issues with the newtonian. While there are newts with no spiders, these
> are not of the $300 variety.
Can you tell us how much a 1 mm wide 3 legged spider will affect the
MTF of the newton? Besides, there are very cheap solutions to get rid
of the diffraction spikes (shown on S&T too).
>
> There are other issues with a $300 Newtonian like light bafflings etc that also
> can degrade the image.
Can you tell us what do you mean by light baffling and how and how
much do they "degrade" an image?
>
> Over the years, there have been many side by side comparisions of a variety of
> scopes, not sure I have seen one of an APO vs. a simple $300 six inch newtonian
> but my guess would be that on planetary detail and on splitting double stars
> that the APO would be superior.
Would you bet? How much?
>
> This is not to say that a 6 inch Newtonian that was built with a good attention
> to detail, could not be superior, just rather as I believe Joe O'neil said, it
> would cost a $1000 or so.
Can't say but I guess that there are cheaper solutions quite as much
effective as more costlier ones. 600 to 700 USD seem a more resonable
cost.
>
> And as someone else pointed out, the real comparison ought to be a 8 inch F6
> Newt because the OTA is only slightly less portable and slightly more expensive
> but the performance gain is substantial.
Then why not make it 10" f/5?
Joseph O'Neil
wrote:
>Not if the stock ones are of a decent make. In other words while it
>might be nicer to have a FeatherTouch or similar (it also looks better
>which is one of the selling points) it not *required* as your original
>post implied.
I was outside lasrt month shooting the moon, trying out two
StellarVue refractors side by side. One had a the regualr rack &
pinion focuser, the second one had the JMI focuser with fine control.
The difference in ease between the two focusers, even for shooting the
moon, was astounding.
In any form of photogrpahy - daytime or astro-photo or
microscopic, form scitntific work to pciutres of your Aunt Matilda the
beach on a Sunday afternoon, you need two things - slow and fine
focus.
Daytime shots - such as point and shoot cameras - you get by
with lousy focus because frequently the lens is stopped down, and also
because, IMO, most hour labs do a terrible job on processing film.
You find a good lab, hang onto them with yrou life.
You see, the eye will forgive a million optical sins whereas
film and CCD will not. The minute you move out of teh realm of day to
day "snapshots', ahving fine and slow focus controls is extremely
critical.
for example, i shoot 4x5 large format film (daytime),a nd in
order to do really big enalrgements - say up to 16x20 is the biggest i
can do in my darkroom - you have to have your focus super critical.
Even for daytime shots, otherwise you loose that look of fine detail
and sharpness. There are other factors to be sure, but ti all starts
with focus,a nd one reaosn 4x5 cameras are so dreadfully expensive i
the precision machining that goes into the focusing system.
The same is true for telescopes. if you ahve a telescope for
visual use, and you want to slap on a 35mm or a digital camera and gor
for some wide angle piggy back shots or some moon shots, go for it.
But if your aim is to get your astro-photo shot on the front
cover of Sky&Telescope or Astronomy magazines, then yes, after a good
mount, your next most important investment will be a good focuser.
You will spend more times and money - and good nights - in wasted
film, then you will have spend on that focusers by the time you
finally luck out and get that good shot.
Look, the difference between a good focusers and a rack and
pinion focuser seen on most telecopes is liekt he difference between a
top of a lien Nikon and your average point and shoot 35mm camera you
buy at Wal-mart, you may not ned the Nikon, or the results fomr yoru
point and shoot may be good enough for you, but there's a reason why
professional cameras cost what they do.
So yes, if you are big time into astro-photo work, not just an
occasional passing fancy, yes, I do beleive a good focuser is
essential, #2 in importance after the mount. In fact, for the record,
the most important items for good astro-photo work, iMO, are:
1) the mount;
2) the mount;
3) the mount;
4) the focuser;
5) the mechanics & maching that hold your optics in place - example,
why pay a fortune for 1/20th wave optics if your mirror or lens cell
is out of alignmne tby 1/1000th of an inch?
6) your optics;
It may sound counter intitive,b ut for astro-photo work - film
or CCD, your mechanics are much more important than your optics.
Optics are only as good as your alignment and collimation,a nd your
ability to use them.
You could have - for arguement's sake - 1/100th wave optics,
but if your optics are pinched, not able to colimate, or if you cannot
fine focus on those pinpoint stars, they will be of no use to you
whatsoever.
joe
Jon Isaacs
>diagonal
>> are issues with the newtonian. While there are newts with no spiders,
>these
>> are not of the $300 variety.
>
>Can you tell us how much a 1 mm wide 3 legged spider will affect the
>MTF of the newton? Besides, there are very cheap solutions to get rid
>of the diffraction spikes (shown on S&T too).
The fact is that diffraction spikes do exist. Someone suggested that optically
there is no advantage of an AOP over a newtonian, I just pointed out that the
$300 Newtonian will have diffraction spikes and effects from the central
obstruction.
No need to calculate MTF, I can see those spikes for myself.
>> There are other issues with a $300 Newtonian like light bafflings etc that
>also
>> can degrade the image.
>
>Can you tell us what do you mean by light baffling and how and how
>much do they "degrade" an image?
Baffles? does the use of baffling in reflectors or refractors need explanation?
>Would you bet? How much?
Wonder how many $300 6 inch Newtonians you have looked through? I have a $450
8 inch Newtonian and I can say that my 120 mm F8.3 achromat does a better job
of splitting double stars than the Newtonian. It might be that tracking at
500X is better for the refractor than for the newtonian, that is certainly a
part of it, the comparison here is between $300 newtonian and an APO.
Side by side tests of top notch 8 inch SCTs and 5 inch APOs (see Todd Gross)
seem to be about neck and neck, so I my money is on the Apo when compared to
the $300 newt.
>Can't say but I guess that there are cheaper solutions quite as much
>effective as more costlier ones. 600 to 700 USD seem a more resonable
>cost.
>
Maybe, don't know of any but for equal quality of construction, we are probably
well over $1000.
>> And as someone else pointed out, the real comparison ought to be a 8 inch
>F6
>> Newt because the OTA is only slightly less portable and slightly more
>expensive
>> but the performance gain is substantial.
>
>Then why not make it 10" f/5?
Good question. Tomorrow I will be picking up a 10 inch F5 DOB which I will
compare with my 8 inch F6 and my 12.5 F4.1, all have essentially the same focal
length. then I can tell you the answer to your question.. <g>
However the issue here is that the OTA of the 8 inch is only somewhat heavier
than that of the 6 inch, about 45% I believe, 19 lbs as opposed to 13lbs, both
very reasonable and the mounts are about the same. However the 10 inch OTAs
are significantly heavier, over 30 lbs, close to the 3 times that of the 6 inch
scope. For many this might be a problem.
Jon Isaacs
Axel
> and the apo. Looking at M42 my dob shows an amazing amount of faint
> detail, but the stars are never perfect balls of fire. In the Stowaway
> the Trapezium is an amazing site, little perfect balls of fire floating
> in space. Same with Albireo, or other double stars. For planetary
> viewing, up to the limits of the aperture, the views are incredibly
> sharp and clear, with absolutely *no* sudden thermal currents to degrade
> the image.
Well a good 8" Newt is quite capable of showing stars as tiny points.
In fact, they should be smaller points than in the 4" refractor! If
they aren't, rest assured that it's not inherent to the Newtonian
design. It simply means that the scope has a problem that needs to be
resolved. It's very likely one of two things:
1. Thermal issues. Can be resolved with good mirror cell design and
having a large enough tube diameter.
2. Optical issues. Can be resolved by upgrading the primary and/or
secondary mirrors to ones with more accurate figures and smoother
surfaces. Or using a coma corrector if the focal ratio is short.
For me, replacing my 8" Dob's stock mirror with a better one took care
of the soft images I was getting. Now it's limited only by seeing
conditions. A comparison of the Trapezium before and after the mirror
swap was revealing. With the new mirror the Trapezium stars focus
down to tiny points and the much-reduced glare from A-D makes E and F
easy to see. With the old mirror I never saw E and F despite repeated
attempts, because of excessive glare from A-D.
Ritesh
Siegfried Gonzi
> Well a good 8" Newt is quite capable of showing stars as tiny points.
> In fact, they should be smaller points than in the 4" refractor! If
> they aren't, rest assured that it's not inherent to the Newtonian
> design. It simply means that the scope has a problem that needs to be
> resolved. It's very likely one of two things:
>
> 1. Thermal issues. Can be resolved with good mirror cell design and
> having a large enough tube diameter.
>
> 2. Optical issues. Can be resolved by upgrading the primary and/or
> secondary mirrors to ones with more accurate figures and smoother
> surfaces. Or using a coma corrector if the focal ratio is short.
>
> For me, replacing my 8" Dob's stock mirror with a better one took care
> of the soft images I was getting. Now it's limited only by seeing
> conditions. A comparison of the Trapezium before and after the mirror
> swap was revealing. With the new mirror the Trapezium stars focus
> down to tiny points and the much-reduced glare from A-D makes E and F
> easy to see. With the old mirror I never saw E and F despite repeated
> attempts, because of excessive glare from A-D.
Hi:
Thank you very much for your account. I very well appreciated it. But be
aware that it will not help much, because the morons who will read your
experiences will move on and next time when this topic appears they will
again throw out the myth "pin point stars are better put into the
refractor realm".
S. Gonzo
Eric Fuller
...
> For me, replacing my 8" Dob's stock mirror with a better one took care
> of the soft images I was getting. Now it's limited only by seeing
> conditions. A comparison of the Trapezium before and after the mirror
> swap was revealing. With the new mirror the Trapezium stars focus
> down to tiny points and the much-reduced glare from A-D makes E and F
> easy to see. With the old mirror I never saw E and F despite repeated
> attempts, because of excessive glare from A-D.
>
just to stir the pot a bit, how much did the original telescope cost ?
how much did the new mirror cost ? what kind of focuser ? is it the
original focuser ?
eric.
Eric Fuller
> Axel wrote:
>
>> For me, replacing my 8" Dob's stock mirror with a better one took care
>> of the soft images I was getting. Now it's limited only by seeing
>> conditions. A comparison of the Trapezium before and after the mirror
>> swap was revealing. With the new mirror the Trapezium stars focus
>> down to tiny points and the much-reduced glare from A-D makes E and F
>> easy to see. With the old mirror I never saw E and F despite repeated
>> attempts, because of excessive glare from A-D.
>
>
>
> Hi:
>
> Thank you very much for your account. I very well appreciated it. But be
> aware that it will not help much, because the morons who will read your
> experiences will move on and next time when this topic appears they will
> again throw out the myth "pin point stars are better put into the
> refractor realm".
>
> S. Gonzo
>
>
I have seen truly terrible diffraction spikes in 6" and 8" newts. i have
also NOT seen terrible spikes in much larger newts (16"). i don't think
changing the primary or the focuser will get rid of the spikes. if we
assume the spider vanes remain the same thickness, do the spikes get
less worse when the aperture goes up ?
eric.
andrea tasselli
> >OK. So telling people that they need expensive focusers regardless of
> >whether the current ones are OK for the job is good for your business.
>
> Remember the context of this discussion and the context of Joe's statement.
>
> Context: the mechanical quality of a $300 Newtonian.
>
> This is what Joe wrote:
>
> "Also bear in mind that, IMO, a $300 newt will nto be as good -
> optical quality speaking - as an $3,000 APO. A really good mirror
> set might cost you $300 alone just for the optics.
>
> By the time youadd good mechanics - a good tube, good mirror
> cell, good focuser - for example, a good JMI or Burgess Focuser - will
> set you back another $300 to $400 alone. Remember that most 4" APOs
> will have focusers that, by themselves, would cost anywhere from $300
> to $500.
> Visually these focusers are wonderful to use, but not
> essential. For imaging however, film or CCD, these focusers are
> pretty much essential for fine, critical focus."
>
> Joe is not trying to sell anything here, rather he is just pointing out that
> the focuser, the cell, the tube are all important parts of the system, it takes
> more than just a decent mirror.
I haven't written he was trying to sell anything, only that he's got a
vested interest in selling astro-stuff there his judgement can be
considered biased (because of this). Promoting "better" astro gear
directly or/and indirectly.
Besides, and this gets to the heart of the question, he wrote
(verbatim):
"For imaging however, film or CCD, these focusers are
pretty much essential for fine, critical focus."
This assertion is, in its entirety, false and misleading with the
current meaning of the word "essential". They might be better but not
essential.
>
> Personally I think it is important to be reasonable with people who are part of
> the industry who choose to post here. They can provide valuable experience and
> see a lot more telescopes of a wider range than the rest of us, their thoughts
> and input are valuable, whether it is Roland Christen or Joe O'neil.
I respectfully disagree.
>
> So, rather than suggest that Joe has a vested interest, just address the facts.
Which I did.
>
> Yes, there focusers on $300 DOBs are not too bad visually, some of them are
> quite decent. But the context is comparing the performance of a $300 Newt to
> that of a $3000 APO and a big part of that difference is in the mechanical
> components.
Not in any essential manner and a trainload of DIY solutions
implemented by amateurs are there to show just that.
Ah, I took the liberty of adding back the trailing 0 you drop in the
price of the APO (I can't quite believe they cost that much!).
andrea tasselli
> >Are you Joe? No? Uncalled for comment -> noise.
> >
>
> I am not Joe but you need to address what he says, not make implications that
> he is interested in trying to sell focusers.
>
> Cheap shot and an uncalled for.
Think of it as it pleases you.
>
> >More specifically, Orion's Europas rack and pinion focusers. All of
> >the right out of the box fine for focusing on a f/5 scope. Don't know
> >about chinese refractors as I would touch 'em with a 10 yard stick.
>
> Then I guess you didn't understand what sort of focusers Joe was talking about.
Well then I think you didn't understand the point I was trying to
make, see my other post.
> >> They are never consistent like the RCF or Televue focusers I have and for a
> >> novice like me, having a quality focuser makes the touchy job of focusing a
> CCD
> >> camera significantly easier.
> >
> >Never try harder, eh?
>
> No reason to make it harder than it already is. But I imagine were you to
> experience a stock Synta focuser you might well change your opinion. Marginal
> for astrophotography.
It may well be. But this wasn't the matter of contention.
Bruce Housey
the view in the 6" because it is brighter. Although the
detail is similar, the brightness makes it easier to see.
This is for a stock $179 Newtonian optical tube (I use
either scope on the same Losmandy GM-8 mount).
On the other hand, the small apo goes with me on vacations
and is also easier to view through for a long time because
I can sit down when viewing through it.
Here are pictures I took of Jupiter through both for
comparison. Hardly scientific since they were taken at
different times, but I think they show that both give
nice views.
apo: http://members.cox.net/bhousey/jupiter_200304122126_tv85_5x.jpg
newt: http://members.cox.net/bhousey/jupiter_and_saturn_20030218.jpg
The best advice is to look through scopes and decide for
yourself. I also love my 8" SCT, but that's another story! :^)
Enjoying whatever I'm using at the time,
Bruce Housey.
Jon Isaacs
>vested interest in selling astro-stuff there his judgement can be
>considered biased (because of this). Promoting "better" astro gear
>directly or/and indirectly.
I suggest that someone in his position has easy access to a broad variety of
equipment, from the $100 Starblaster type scope on up the line to some of the
best. Thus rather than being biased, it actually might be more objective than
mine or yours.
Something to consider.
>
>"For imaging however, film or CCD, these focusers are
> pretty much essential for fine, critical focus."
>This assertion is, in its entirety, false and misleading with the
>current meaning of the word "essential". They might be better but not
>essential.
The phrase "pretty much essential" does not mean something is essential, rather
it means it is desireable and a damn good idea if you can do it.
I would guess that you agree a smooth focuser with no slop in the rack and
without rock is "pretty much essential."
>> So, rather than suggest that Joe has a vested interest, just address the
>facts.
>
>Which I did.
Then there is no need to bring up the vested interest in the first place. We
all have vested interests in one way or another.
>> Yes, there focusers on $300 DOBs are not too bad visually, some of them are
>> quite decent. But the context is comparing the performance of a $300 Newt
>to
>> that of a $3000 APO and a big part of that difference is in the mechanical
>> components.
>Not in any essential manner and a trainload of DIY solutions
>implemented by amateurs are there to show just that.
There are DIY solutions however and these do work. But overall, producing a
scope that is solid and doesn't have workarounds it will take some money.
Having a solid mechanical system supporting the telescope optics is an
important part of the system. One only has to look at the difference in
construction of a professional and amateur scopes and mounts to see what a 12
or 20 inch amateur scope would cost were they built to same level as an APO.
By the way, I am not an owner of an expensive APO defending their honor.
Rather I am the owner of some inexpensive Newtonians that have those sorts of
DIY and hokey stuff on them.
Things could be better but I aint buying an APO when a 10 inch DOB fits in my
trunk.
jon isaacs
Jon Isaacs
Scott
<joni...@aol.com> wrote:
>
> Context: the mechanical quality of a $300 Newtonian.
>
I agree that a $300 6" F8 Newtonian will have a cheap feel because of
the inexpensive components. Why don't we change the goal? How about a
$1,200 6" F6 Newtonian with an aluminum or carbon fiber tube, excellent
optics, a quality focuser and a good secondary. You could even go the
window route if you want to get away from spider diffraction. I would
argue that this telescope should be superior to a 4" apo in every way,
with the exception of wide field photography. I am not aware of
anything like this on the market.
Comments?
Chris1011
$1,200 6" F6 Newtonian with an aluminum or carbon fiber tube, excellent
optics, a quality focuser and a good secondary. You could even go the
window route if you want to get away from spider diffraction. I would
argue that this telescope should be superior to a 4" apo in every way,>>
Actually it wouldn't, but an 8" F5 would, and be quite nice in a carbon fiber
tube. Years ago I saw a proposed design by Buchroeder with a 45 degree window.
The diagonal was an aluminized spot right on the window. This window would be
multi-coated to eliminate any possibility of ghost images. This scope had a
built-in zoom optical system that would produce 50x to 500x with approx 70
degree field, if I remember right.
Actually, if you go to all the trouble to produce a window with 1/10 wavefront,
you might as well curve it and make it into a Mak. Coma is essentially gone
then.
Roland Christen
Alan French
The problem is that we use one single term, "portable," to address a host of
issues. To me, it translates into how easy the scope is to get in and out
of our ground level basement, and in and out of the car. With this view, I
do find the AP Traveler and the RV-6 quite comparable.
There are many issues that concern portability, Size or "bulk" can be a big
issue if you have limited storage, restricted exit from the storage area
(stairs, in particular), or a small car. For some people, weight is a big
concern, and we all have our limits there. For me, two big concerns are
ease of assembly and the number of trips required to get all the parts out
of the house (or, more importantly, back into the house).
Even a 4" APO is more than I want to put in a backpack, especially
considering you need a good mount too.
Clear skies, Alan
"Tony Flanders" <tony_f...@yahoo.com> wrote in message
> [SNIP]
Axel
> how much did the new mirror cost ? what kind of focuser ? is it the
> original focuser ?
Well everything but the actual Sonotube of the original 8" f/6
Celestron Star Hopper has been replaced. I bought the scope new for
$500; the new primary was $700 (R.F. Royce). I swapped the stock
1.25" focuser with a JMI 2" Crayford model. And replaced the
secondary mirror, spider, mount, and mirror cell. It really is a
completely different scope than when I got it... :)
Ritesh
clyde crewey
I too have a TV85 and a 6" f/8 Newt. I agree detail seen is similar
though the C ring of Saturn is much easier to see in the 6". Cassini
is blacker as well. Can't beat the 85 APO for travelling, terrestrial
use and for bang for the aperture. Can't beat the Dob for bang for
the buck! By the way, stars are absolute pinpoints in my 6" f/8.
I've compared it not only to my TV85, but also to a TV Pronto/Ranger,
TV76, Tak 78, and Tak 102 for refractors. I've only compared it with
a C8 and XT8 as far as non-refractors. The contrast is better in the
TV85 and also the above refractors, but star images are virtually
identical.
Clyde
Bruce Housey <bruce...@yahoo.com> wrote in message news:<8Hdqa.277179$S14.1...@news1.central.cox.net>...
Jon Isaacs
>the inexpensive components. Why don't we change the goal? How about a
>$1,200 6" F6 Newtonian with an aluminum or carbon fiber tube, excellent
>optics, a quality focuser and a good secondary. You could even go the
>window route if you want to get away from spider diffraction. I would
>argue that this telescope should be superior to a 4" apo in every way,
>with the exception of wide field photography. I am not aware of
>anything like this on the market.
>
>Comments?
I believe there are 6 inch Mak-Newts that might be in this price range.
But if you are going to make such a scope as a classical newtonian, it is
probably smarter to make it a 8 inch F6 and give some more bite.
As far as being superior to an APO in everyway except widefield viewing, I
can't say. Certainly the portability issue has not been addresss, the 36 inch
OTA is long.
It will still probably have thermal management problems that mean cool down
takes some real time.
Seems to me that when compared to the APO:
Be less portable.
Require longer cool downs
Have a significantly narrower field of view
Not as versatile, terrestrial is not a strengh for the newtonian.
But myself I am not going to buy either one. Because for $1200, I could come
close to buying a 12.5 inch F5 mirror Mike Spooner mirror and have myself one
hell of a scope.
Problem with an 6 inch F6 OTA is that still would need an mount, that mount
would have to be substantially heavier than the mount required for the APO and
aperture wise it would suffer when compared to larger Newtonians.
There are many choices here and it seems to me that a 6 inch newtonian is too
big to be really easily transported without a car. So the next barrier is what
fits easily in a car and that is somewhere between a 8 inch F6 scope and a 10
inch scope.
Aperture is pretty hard to beat.
Jon
Jose Suro
are manufactured to the best specifications known to man. They are the best
examples of the builder's exacting care in designing and constructing an
instrument with supreme optical qualities - for their size. Nevertheless,
they remain... 4" scopes. The laws of physics overwhelm them. "Tiny" is the
key word in the vocabulary of all astronomers worth their salt- especially
in this day and age of excellent 36" scopes and 70mm binoculars of very high
quality all available to the public - and also with the increasing quality
from all sources in all scopes.
Any larger and decent scope will present a 4" APO with an insurmountable
challenge- in any category. There is an allure to owning the best there is,
and the best is usually expensive. 4" APOs are that, but also within the
realm of most budgets, and you are assured of the best there is - for the
aperture. This does not make them comparable to any decent scope with a
bigger aperture.
And more so, from all the images, in most all applications, I've seen on
the net the Astro-Physics Mak-Cass are the winners. This from an APO supreme
designer and builder.
And so, IMHO the compound telescopes, even in the smaller apertures, win,
and they win hands down.
Take Care,
JAS
I fully understand this.
Dan Chaffee
>>> The diffraction spikes of the spiders the diffraction effects of the
>>diagonal
>>> are issues with the newtonian. While there are newts with no spiders,
>>these
>>> are not of the $300 variety.
>>
>
>>Can you tell us how much a 1 mm wide 3 legged spider will affect the
>>MTF of the newton? Besides, there are very cheap solutions to get rid
>>of the diffraction spikes (shown on S&T too).
>
>The fact is that diffraction spikes do exist. Someone suggested that optically
>there is no advantage of an AOP over a newtonian, I just pointed out that the
>$300 Newtonian will have diffraction spikes and effects from the central
>obstruction.
>
>No need to calculate MTF, I can see those spikes for myself.
There is no noticeable degradation of detail *on* objects from
spider vanes unless they are needlessly thick. Aesthetically
speaking of course, objection to spikes is a legitimate complaint.
>
>>> There are other issues with a $300 Newtonian like light bafflings etc that
>>also
>>> can degrade the image.
>>
>>Can you tell us what do you mean by light baffling and how and how
>>much do they "degrade" an image?
>
>Baffles? does the use of baffling in reflectors or refractors need explanation?
Annular baffels in a standard open ended reflector can (and do)
cause tube currents to pass into the optical path. If you're into high
resolution work, other baffleing options should be used for open
tube instruments.
>Wonder how many $300 6 inch Newtonians you have looked through?
My 6" f/8.4 newtonian cost about $150 to make and allows for the
detection of Regio Galileo on Ganymede at 360x+. Will a 4" APO
do that?
>I have a $450
>8 inch Newtonian and I can say that my 120 mm F8.3 achromat does a better job
>of splitting double stars than the Newtonian. It might be that tracking at
>500X is better for the refractor than for the newtonian, that is certainly a
>part of it, the comparison here is between $300 newtonian and an APO.
Jon, something is not right. Unless the mirror isn't cooled, is out of
collimation, or has a bad figure, there is no reason a 120mm refractor
should split double stars with greater ease. Even a 200mm reflector
with the industry standard .8 strehl should out resolve double stars
over 120mm of refractor. The diffraction patterns are usually stabler
in the smaller closed tube instrument, but that doesn't mean it
can't be beaten resolutionwise by the larger reflector for at least
some of the time.
Dan Chaffee
Joe Bergeron
<jas...@attglobal.net> wrote:
> "Tiny" is the
> key word in the vocabulary of all astronomers worth their salt- especially
> in this day and age of excellent 36" scopes and 70mm binoculars of very high
> quality all available to the public
So...your definition of a worthwhile astronomer is one who considers a
4" scope to be uselessly tiny, or in other words, one who agrees with
you. I've seen too many exquisite things in scopes of this size to take
that opinion seriously.
A 36" scope of any kind is far more than I want to handle. I wouldn't
take one if you gave it to me. To me it would be a useless white
elephant.
--
Joe Bergeron
Siegfried Gonzi
> I have seen truly terrible diffraction spikes in 6" and 8" newts. i have
> also NOT seen terrible spikes in much larger newts (16"). i don't think
> changing the primary or the focuser will get rid of the spikes. if we
> assume the spider vanes remain the same thickness, do the spikes get
> less worse when the aperture goes up ?
>
> eric.
>
Hi:
Theoretically they would indeed affect the MTF, but the amount of this
suffering is that small, so to speak, that you could easily forget it.
What severely affects the MTF is the diameter of the secondary itself.
But also in this case people become deceived by the lunatics, because
when you often hear: in order to compete against a refractor you
actually need a Newtonian with 20% obstruction or less. This has some
truth but only then if you compare scopes with the same /diameter/.
A 6" Newtonian with lets say 30% obstruction will always win against a
lets say 4" apochromat, even the Newtonian features 30% obstruction. The
refractor lunatics haven't come up yet with a solution why this might be
so, because in their brains the old saying goes: "It needs a scope with
20% obstruction or less in order that it can stack up against an
apochromat".
S. Gonzi
Siegfried Gonzi
> I have an 85mm APO and 6" f/8 Newt and personally prefer
> the view in the 6" because it is brighter. Although the
> detail is similar, the brightness makes it easier to see.
> This is for a stock $179 Newtonian optical tube (I use
> either scope on the same Losmandy GM-8 mount).
>
> On the other hand, the small apo goes with me on vacations
> and is also easier to view through for a long time because
> I can sit down when viewing through it.
>
> Here are pictures I took of Jupiter through both for
> comparison. Hardly scientific since they were taken at
> different times, but I think they show that both give
> nice views.
>
> apo: http://members.cox.net/bhousey/jupiter_200304122126_tv85_5x.jpg
>
> newt: http://members.cox.net/bhousey/jupiter_and_saturn_20030218.jpg
Hi:
Nice. It needs more reports like yours. And by the way if you had a 6"
Dob with definite mirror accuracy (I mean some high quality mirror), you
would report here that the view through this Dob blows away your view
through your 85mm apo.
Anyway a low cost Dob with mediocore mirror accuracy and figuring is
better than a 85mm apo, even.
A short note: have you ever checked wether your mirror is properly aligned?
S. Gonzi
Jon Isaacs
>There is no noticeable degradation of detail *on* objects from
>spider vanes unless they are needlessly thick. Aesthetically
>speaking of course, objection to spikes is a legitimate complaint.
Someone had commented that optically the larger Newtonian should be better in
everyway but FOV. I was just pointing out that there are spikes which are a
problem that refractors do not have. And of course, it is not only an
aesthetic problem is a faint companion happens to fall on the diffraction
spike.
>Jon, something is not right. Unless the mirror isn't cooled, is out of
>collimation, or has a bad figure, there is no reason a 120mm refractor
>should split double stars with greater ease.
>The diffraction patterns are usually stabler
>in the smaller closed tube instrument, but that doesn't mean it
>can't be beaten resolutionwise by the larger reflector for at least
>some of the time.
>
Given the issue of the spikes plus the fact that the 120mm refractor sits on a
stable tracking mount which allows focusing without vibration at high powers
rather than a DOB mount, it does a better job almost all the time.
Maybe if the Newtonian were on a stable tracking mount and it were nicely
cooled down and the seeing was good, then I would expect it to be better.
I would agree that probably the larger refractor, under the right circumstances
would beat it out resolution wise. But I have been able to split 1.3 arc
second doubles with the refractor which is getting close to the limit and
trying to hand track at the powers necessary to split 1.3 arc second doubles is
difficult.
Note that I am including the mount in this because I believe that one needs to
evaluate the telescope as a system.
My overall thinking is that smaller scopes are less sensitive to many issues
such as thermal equilibrium and seeing plus it is obviously easier to make a
small mirror or optic precisely than a large one.
So it seems that it is easier to build a smaller scope that approaches the
limits of what is theoretically possible and it will approach its limits more
of the time.
Jon Isaacs
Jose Suro
>"I've seen too many exquisite things in scopes of this size..."
So have a gazillion others, yours truly included. I get some of the best
views in my "tiny" but excellent 70mm binoculars.
>"...to take that opinion seriously."
No problem, but your conclusion is based on incorrect antecedents. It is
based on your infusion of the word "uselessly" as a modifier to the word
"tiny", which you seem to be taking as derogatory. You took that
interpretative leap all by yourself with no support from my original
argument. Nowadays, astronomers are looking at the sky with telescopes
measured in multiples of meters. In that context, a 4" scope is indeed tiny.
Take Care,
JAS
"Joe Bergeron" <jaber...@earthlink.nettled> wrote in message
news:250420032344305489%jaber...@earthlink.nettled...
Eric Fuller
> Eric Fuller wrote:
>
>> I have seen truly terrible diffraction spikes in 6" and 8" newts. i
>> have also NOT seen terrible spikes in much larger newts (16"). i don't
>> think changing the primary or the focuser will get rid of the spikes.
>> if we assume the spider vanes remain the same thickness, do the spikes
>> get less worse when the aperture goes up ?
>>
>> eric.
>>
>
> Hi:
>
> Theoretically they would indeed affect the MTF, but the amount of this
> suffering is that small, so to speak, that you could easily forget it.
>
> What severely affects the MTF is the diameter of the secondary itself.
> But also in this case people become deceived by the lunatics, because
> when you often hear: in order to compete against a refractor you
> actually need a Newtonian with 20% obstruction or less. This has some
> truth but only then if you compare scopes with the same /diameter/.
20%. I'm really interested in the effect of the vanes as we change the
size of the aperture. Keep everything else the same, 20% CO, common vane
size (maybe 1mm), but compare a 6" Newt to a 16" Newt. Let's look at a
star. Which of these two whould show more prominent spikes due to the
vanes ? Intuition tells me the 6" would show brighter spikes compared to
the image of the star. And maybe fatter spikes as well. I only have one
Newt (8") so I can't compare to anything else. I am suggesting that as
the aperture goes up, the problem of spikes goes down.
Eric.
andrea tasselli
> On 25 Apr 2003 01:17:55 -0700, atas...@hotmail.com (andrea tasselli)
> wrote:
>
> >Not if the stock ones are of a decent make. In other words while it
> >might be nicer to have a FeatherTouch or similar (it also looks better
> >which is one of the selling points) it not *required* as your original
> >post implied.
>
....
>
> You see, the eye will forgive a million optical sins whereas
> film and CCD will not. The minute you move out of teh realm of day to
> day "snapshots', ahving fine and slow focus controls is extremely
> critical.
I wouldn't say so or I least wouldn't say it requies a 300 bucks
focuser.
>
> for example, i shoot 4x5 large format film (daytime),a nd in
> order to do really big enalrgements - say up to 16x20 is the biggest i
> can do in my darkroom - you have to have your focus super critical.
> Even for daytime shots, otherwise you loose that look of fine detail
> and sharpness. There are other factors to be sure, but ti all starts
> with focus,a nd one reaosn 4x5 cameras are so dreadfully expensive i
> the precision machining that goes into the focusing system.
>
> The same is true for telescopes. if you ahve a telescope for
> visual use, and you want to slap on a 35mm or a digital camera and gor
> for some wide angle piggy back shots or some moon shots, go for it.
>
> But if your aim is to get your astro-photo shot on the front
> cover of Sky&Telescope or Astronomy magazines, then yes, after a good
> mount, your next most important investment will be a good focuser.
> You will spend more times and money - and good nights - in wasted
> film, then you will have spend on that focusers by the time you
> finally luck out and get that good shot.
I have to disagree completely with the above, both for theorethical
reasons and both for experience. In between a crappy shot at the moon
and S&T (besides I was published several times in my own country's
astronomy magazines) gallery there are several thousand shades of
abilities and results and most of us fit in there. So maybe if I had a
terrific mount, aperture in spades, a topnotch CCD system and
wonderful seeing then, but only then, I would worry about not having a
focuser capable of fraction of a hundredth of mm precision. Being
limited in all the above (the most serious being the seeing after the
mount) I can still shot frames at 2" fwhm raw with my substandard
(according to you) focuser which isn't really too bad given my setup.
andrea tasselli
It doesn't if you keep the relative size of the vanes equal, as it
should be because of stiffness requirements.
smsastro
> the aperture goes up, the problem of spikes goes down.
>
> Eric.
Hi Eric,
The spikes in my current 10" f5 Newt are far less obvious than in an
excellent 6" f8 Newt that I used to own. They're both 4 vane spiders.
Clear Skies,
Steve
andrea tasselli
> >> The diffraction spikes of the spiders the diffraction effects of the
> diagonal
> >> are issues with the newtonian. While there are newts with no spiders,
> these
> >> are not of the $300 variety.
> >
>
> >Can you tell us how much a 1 mm wide 3 legged spider will affect the
> >MTF of the newton? Besides, there are very cheap solutions to get rid
> >of the diffraction spikes (shown on S&T too).
>
> The fact is that diffraction spikes do exist. Someone suggested that optically
> there is no advantage of an AOP over a newtonian, I just pointed out that the
> $300 Newtonian will have diffraction spikes and effects from the central
> obstruction.
So very bright objects (stars) might have spikes, so what? Some think
they are even nicer to see with them on! And I don't see why a 300,000
$ newton, if equipped with a secondary spider, shouldn't have any.
>
> No need to calculate MTF, I can see those spikes for myself.
You would if you're interested in knowing how much detrimental they
are (very very little is the answer).
>
> >> There are other issues with a $300 Newtonian like light bafflings etc that
> also
> >> can degrade the image.
> >
> >Can you tell us what do you mean by light baffling and how and how
> >much do they "degrade" an image?
>
> Baffles? does the use of baffling in reflectors or refractors need explanation?
Yes it does as you wrotethat baffles are detrimental. Can you tell me
how?
>
>
> >Would you bet? How much?
>
> Wonder how many $300 6 inch Newtonians you have looked through? I have a $450
> 8 inch Newtonian and I can say that my 120 mm F8.3 achromat does a better job
> of splitting double stars than the Newtonian. It might be that tracking at
> 500X is better for the refractor than for the newtonian, that is certainly a
> part of it, the comparison here is between $300 newtonian and an APO.
I have one and looked through quite a number.
>
> Side by side tests of top notch 8 inch SCTs and 5 inch APOs (see Todd Gross)
> seem to be about neck and neck, so I my money is on the Apo when compared to
> the $300 newt.
How come Todd Gross is the definitive answer to optical diatribes? Has
he been invested by some international commitee to oversee the optical
quality of amateur scopes? However, the scope I have in mind has
russian optics and gives any damn 4" APO a run for its money and then
there's some more left to spare. The only thing the newton is lacking
is very large FOV (and I mean very very large) but that's an issue
only for some people.
>
>
> >Can't say but I guess that there are cheaper solutions quite as much
> >effective as more costlier ones. 600 to 700 USD seem a more resonable
> >cost.
> >
>
> Maybe, don't know of any but for equal quality of construction, we are probably
> well over $1000.
They're not comparable so I don't see why do you want to compare two
telescopes with totally different design.
Eric Fuller
Eric.
Bruce Housey
>
> Nice. It needs more reports like yours. And by the way if you had a 6"
> Dob with definite mirror accuracy (I mean some high quality mirror), you
> would report here that the view through this Dob blows away your view
> through your 85mm apo.
Thanks. I have considered what a better mirror would do... hard
to imagine it getting much better for 6" though.
> Anyway a low cost Dob with mediocore mirror accuracy and figuring is
> better than a 85mm apo, even.
The beauty of 6" f/8, as I understand it, is that it would be
diffraction limited even if they didn't bother parabolizing at
all! (just leave it spherical) This makes this particular scope
easy to build on the cheap.
> A short note: have you ever checked wether your mirror is properly aligned?
Absolutely... I use the Tectron tool set and align all the way
down to the autocollimator, then fine tune with star test before
photographing. I only take a picture or two a night, but I try
to make them count. My main scope for the last three years is
an 8" SCT, so I now dream about collimation! :^)
Alan French
A 6" f/8 is too short to leave spherical. An f/10 would work reasonably
well, but it should be f/12 or 13 to really shine.
Clear skies, Alan
"Bruce Housey" <bruce...@yahoo.com> wrote in message
news:DqGqa.4492$Cm3...@news1.central.cox.net...
> [SNIP]
> The beauty of 6" f/8, as I understand it, is that it would be
> diffraction limited even if they didn't bother parabolizing at
> all! (just leave it spherical) This makes this particular scope
> easy to build on the cheap.
> [SNIP]
Jon Isaacs
> Some think
>they are even nicer to see with them on! And I don't see why a 300,000
>$ newton, if equipped with a secondary spider, shouldn't have any.
>> No need to calculate MTF, I can see those spikes for myself.
>
>You would if you're interested in knowing how much detrimental they
>are (very very little is the answer).
Someone suggested that wide field viewing was the only advantage of a APO.
I just pointed out that indeed a $300 Newtonian will have diffraction spikes.
This is an obvious difference.
If someone likes diffraction spikes then I suggest putting some false vanes in
all their scopes.
Jon Isaacs
Jon Isaacs
andrea tasselli
If of the same size, yes of course.
rande...@rogers.com
I used to like them in deepsky photographs.
-Rich
William R. Mattil
Jon Isaacs <joni...@aol.com> wrote:
>
>Given the issue of the spikes plus the fact that the 120mm refractor sits on a
>stable tracking mount which allows focusing without vibration at high powers
>rather than a DOB mount, it does a better job almost all the time.
Open Mouth ... Insert foot.
Jon you do realise that this last statement
contradicts your previous assertations that stability while focusing is
a strength of the Dob mount vs the GEM ?!?!?! Which is it Jon ?
Maybe that Gonzi has a valid point here eh ?
>Maybe if the Newtonian were on a stable tracking mount and it were nicely
>cooled down and the seeing was good, then I would expect it to be better.
Your previous arguments with me over the huge advantages of the Dob mount
over the GEM would indicate that this is not a true statement. Or that you
just like to tilt at windmills.... which is it ?
Bill
--
William R. Mattil | Dogbert: That's circular reasoning.
Sr. System Aministrator | Dilbert: I prefer to think of it as no
(972) 399-4106 | loose ends.
Scribe2b
>a
>>stable tracking mount which allows focusing without vibration at high powers
>>rather than a DOB mount, it does a better job almost all the time.
>
>Open Mouth ... Insert foot.
jon is clearly saying that long-term viewing is best with stable tracking. and
that the moment of focusing is always more stable with a Dob mount. i see no
contradiction in jon's entire post. i find the same.
William R. Mattil
"Clearly" you shouldn't put words in Jon's mouth. But ... you point is
noted and I will add your name to the Jon Issac's bad argument fan club.
Let me type this more slowly so that even the learning impaired can
read it :^)
Jon uttered in a flash of brilliance
"Given the issue of the spikes plus the fact that the 120mm refractor sits on
a stable tracking mount which allows focusing without vibration at high powers
rather than a DOB mount, it does a better job almost all the time."
The tracking has no bearing at all on the stability while focusing. Period.
Jon has stated previously many, many times that a Dob is more stable than
a GEM and he mentioned that focusing was "more stable" with the Dob.
*Clearly* he cannot seem to make up his mind. :^)
Jon Isaacs
>>Given the issue of the spikes plus the fact that the 120mm refractor sits on
>a
>>stable tracking mount which allows focusing without vibration at high powers
>>rather than a DOB mount, it does a better job almost all the time.
>Open Mouth ... Insert foot.
>
>Jon you do realise that this last statement
>contradicts your previous assertations that stability while focusing is
>a strength of the Dob mount vs the GEM ?!?!?! Which is it Jon ?
I happen to have the 120 mm refractor sitting on a 1950's Houston-Fearless
Cinematic/TV tripod.
This is what Astrophotographer Jerry Lodriguss has to say about this tripod:
(http://www.astropix.com/HTML/I_ASTROP/I02/I02.HTM)
"The CECO tripod was an incredibly lucky find. It is a tripod that was made
probably 30 years ago for professional video and cinematography. Along with its
near twin made by Houston Fearless, these two brands of tripods are not
manufactured anymore, with most still being in service at television studios,
so they do not come onto the market frequently. The tripod has adjustable legs
for the height, and a custom made assembly on top that mates with the telescope
mounting. Although the CECO and Houston Fearless tripods are nearly impossible
to find these days, Losmandy and Astro-Physics both made substantial portable
piers that work very well with their mountings."
You might notice in the picture that all his control equipment is mounted on
the tripod.
I have only found a few references to this tripod on the net. Jerry's is one,
old TV studio webpages have a few shots, and there was a page that advertised
one for sale. That page disappeared when the tripod sold.
It was advertised at $750 and it was claimed to have cost $4000 new when
equipped with spreader feet and wheels.
So, in this case, working at 500x with a CG-5 mounted on mounted on the
Houston-Fearless tripod, the refractor is stable, I can even focus it without
significant vibration problems at 500X.
So, if you have a friend like I do with an eagle eye and sees one of the these
tripods at a garage sale for $20, I recommend getting one. (Thanks again Bob)
>Your previous arguments with me over the huge advantages of the Dob mount
>over the GEM would indicate that this is not a true statement. Or that you
>just like to tilt at windmills.... which is it ?
On the orignal tripod, the scope could not be operated at over 100X because the
stepper motors would cause vibration which would blurr the image. To split the
double-double clearly, I had to turn the motors off.
Swapping tripods was quite an amazing transformation.
So, there is no doubt that for high power work a tracking mount of some type is
desireable. The fact that I was able to secure a rock steady tripod for $20
allows my cheap refractor to perform very nicely at high powers.
This of course is relevent to my overall point because unlike that $300 6 inch
Newtonian, a 4 inch APO is likely to be sitting on a tripod that, while maybe
not designed for Hollywood studios and 200 TV camera like the Houston-Fearless,
are certainly adequately stable.
--------------------
My feet are solid on the floor, I can see the blood dripping where you bit your
ankle.
Jon Isaacs
William R. Mattil
Jon Isaacs <joni...@aol.com> wrote:
>
[general backpeddaling snipped]
>So, in this case, working at 500x with a CG-5 mounted on mounted on the
>Houston-Fearless tripod, the refractor is stable, I can even focus it without
>significant vibration problems at 500X.
So in your most expert opinion then the CG-5 Mount is a very stable platform
for a telescope ? In fact (your own words here), more stable than a Dob ?
I realise that you are old and getting forgetful but any deja-news search
will turn up multiple posts of yours where you argued, without merit is seems,
the point that a Dob is more stable than a GEM. Some of your arguments were
so pathetic that I even saved them for club meeting humor ..... :^)
>My feet are solid on the floor, I can see the blood dripping where you bit your
>ankle.
If your feet are on the floor then your head must so deeply entrenched
within the darkness of your rectum that you still can't see the light of day.
Thanks for sharing this and all of your other irrational arguments though.
And to set the record straight Pal, I am not changing my tune in the least.
A GEM is more preferable to a Dob mount. I wonder though ... can you say
the same ? :^)
Bill
--
William R. Mattil | If Con is the opposite of Pro .... Then
Sr. System Aministrator | is Congress the opposite of Progress ? -
(972) 399-4106 | Gallagher
Jon Isaacs
>for a telescope ? In fact (your own words here), more stable than a Dob ?
In my expert opinion, this CG-5 mount, sitting at top a Houston-Fearless Tripod
that reportedly cost someone about $4000 in 1960's money, it certainly stable
enough to handle a 10 pound 40 inch long optical tube.
Whether it is stable enough to handle and 45 inch 19 inch Optical tube of an 8
inch F6, I will soon find out.
>I realise that you are old and getting forgetful but any deja-news search
>will turn up multiple posts of yours where you argued, without merit is
>seems,
>the point that a Dob is more stable than a GEM.
The last time you suggested that someone do a deja-news search, I challenged
you to do so and at that point, you just dropped out.
This is my thinking:
It is clear that it is possible to design and build an EQ mount with a tripod
that is stable and solid. It is also clear that it is easier and less
expensive to build a DOB mount that is stable and equally solid. Inexpensive
scopes sitting on EQ mounts are normally under mounted.
The issue in this case, is simply that tracking at 500X is not that easy with a
DOB mount, no matter how stable it might be.
>And to set the record straight Pal, I am not changing my tune in the least.
>A GEM is more preferable to a Dob mount. I wonder though ... can you say
>the same ? :^)
I have that Gem mount, but interestingly I just took to OTA off and store it,
lower the legs and put the Mount in the corner.
This was to make way for another DOB.
Hopefully I will find that the CG-5 is substantial enough to handle an 8 inch
F6 Newtonian. Normal thinking is that it would not be suffient, but I am
hoping that with the superior tripod that it will handle it.
jon
William R. Mattil
Jon Isaacs <joni...@aol.com> wrote:
>>So in your most expert opinion then the CG-5 Mount is a very stable platform
>>for a telescope ? In fact (your own words here), more stable than a Dob ?
>
>In my expert opinion, this CG-5 mount, sitting at top a Houston-Fearless Tripod
>that reportedly cost someone about $4000 in 1960's money, it certainly stable
>enough to handle a 10 pound 40 inch long optical tube.
For the record then, you are recanting your earlier assertations that a GEM
is inferior to a DOB. I want to make sure that I get this right. You and
I have had many discussions on this and you have *always* contended that
the DOB was more stable. Now it seems you are changing your tune. You
seem to be missing this point and I want to make certain that you get it
OK ? And forget the bullshit about your $4,000 tripod okay ? Thats just
a smokescreen. I am certain that my pier(s) and tripods are more than
equal to your tripod and none of them cost anything remotely resembling
$4,000.00. :^)
>Whether it is stable enough to handle and 45 inch 19 inch Optical tube of an 8
>inch F6, I will soon find out.
Okay professor which is it ? 45 inch ? or 19 inch ? sheesh .....
> I wrote:
>>I realise that you are old and getting forgetful but any deja-news search
>>will turn up multiple posts of yours where you argued, without merit is
>>seems,
>>the point that a Dob is more stable than a GEM.
>
>The last time you suggested that someone do a deja-news search, I challenged
>you to do so and at that point, you just dropped out.
Why should I have to do this ? Any s.a.a. reader with half a brain will
remember your allegations and your arguments extolling the virtues of
the DOB mount vs the GEM. I would be more than happy to wager a sum of
money on this though ...... It is a sure thing :^) You simply choose to
not remember it. For a supposedly intelligent man you seem to suffer
from selective memory.
>This is my thinking:
>
>It is clear that it is possible to design and build an EQ mount with a tripod
>that is stable and solid.
It is, and they are sold every day.
AstroPhysics, Parallax Instruments, Losmandy, Mountain Instruments, Parks etc
There are others. All of these are far more stable than any DOB.
> It is also clear that it is easier and less
>expensive to build a DOB mount that is stable and equally solid. Inexpensive
>scopes sitting on EQ mounts are normally under mounted.
Doh! .... Lets compare a Porsche to an AMC Gremlin why don't we... sheesh.
But my statement still stands as incontravertable. A stable GEM is more
stable than a stable DOB.
>The issue in this case, is simply that tracking at 500X is not that easy with a
>DOB mount, no matter how stable it might be.
In all of our discussions regarding the relative merits of DOBs vs GEMs I
have always said this very same thing and you have ignored it. Now you
choose to bring it up to support your apparent change of position ?!?!?!?
>Hopefully I will find that the CG-5 is substantial enough to handle an 8 inch
>F6 Newtonian. Normal thinking is that it would not be suffient, but I am
>hoping that with the superior tripod that it will handle it.
This is funny .... Enjoy your superior GEM. I have never doubted that a GEM
is superior to a DOB. But it is interesting to note how you have changed
your tune and yet at the same time refuse to admit that you have done so.
We now return to our regularly scheduled programming.
Brian Tung
> For the record then, you are recanting your earlier assertations that a GEM
> is inferior to a DOB. I want to make sure that I get this right.
Maybe you don't intend to, but you also sound like you want to make sure
you win the argument. Sounds like Jon was ambiguous (or he exaggerated),
and you're giving him a multiple choice opportunity to clarify or correct,
but the choices are endpoints only: always the dob, or always the GEM.
That's just the way it seems to me. I'm sure this would all be clearer in
person (and more pleasant, I suspect), but as it so happens, we're not
talking in person.
Maybe the $4,000 was a smoke screen. Does that mean that it's totally
irrelevant? Is cost a potential issue? It might or might not be, but
that's a testable assertion and finding out if that's what he meant,
without throwing "forget the bullshit" or "OK, professor" around, sounds
like a good idea to me. Then you can put some price and measurement data
on it.
Jon, it does seem like it could use some clarifying: In your opinion,
under what conditions (cost, application, operating environment, etc)
would, say, a 6-inch f/8 Newtonian be more stable on a Dobsonian mount
than a GEM? Under what conditions would it be equally stable? Less
stable?
Brian Tung <br...@isi.edu>
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
Jon Isaacs
>8
>>inch F6, I will soon find out.
>
>Okay professor which is it ? 45 inch ? or 19 inch ? sheesh .....
I need to correct what I had written, I imagine most readers figured out that
what I meant to say was a 45 inch, 19 pound optical tube.
jon Isaacs
William R. Mattil
>
>Maybe you don't intend to, but you also sound like you want to make sure
>you win the argument.
Actually Brian its not really an argument. I am certain that I remember
quite well his previous comments on this topic. The problem with comments
such as Jon made/makes is that they are never qualified. He has stated
"A DOB is more stable than a GEM"
Nothing about specifics. Had he bothered to provide pertainent details
it would have been infinitely more valuable to someone seeking information.
It is/was a easy task to think of instances where his blanket statement is
not true at all. He consistantly refuses to accept this.
>Sounds like Jon was ambiguous (or he exaggerated),
>and you're giving him a multiple choice opportunity to clarify or correct,
>but the choices are endpoints only: always the dob, or always the GEM.
>That's just the way it seems to me.
You betcha. I am wise enough to know that there are advantages to both and
that one is *never* always better. But his arguments against the GEM were
always slanted (read as biased) in favor of the DOB. I am at a loss to
explain why he needs to do this but hey ... it is after all s.a.a.
>I'm sure this would all be clearer in
>person (and more pleasant, I suspect), but as it so happens, we're not
>talking in person.
>
>Maybe the $4,000 was a smoke screen. Does that mean that it's totally
>irrelevant?
In my view ? Yes ... I am certain that a Losmandy G-11 would be far
more stable than his $4,000.00 tripod with a CG-5 :^) And cheaper.
>Is cost a potential issue? It might or might not be, but
>that's a testable assertion and finding out if that's what he meant,
>without throwing "forget the bullshit" or "OK, professor" around, sounds
>like a good idea to me. Then you can put some price and measurement data
>on it.
There were opportunities when the original assertions were made. I have
previously explained that pontification on a given subject without
meaningful data is useless and tends to confuse the less informed. For
example:
"A Celestron rockhopper Dob is more stable IMHO than a flybynite GEM"
Can certainly be argued but there are specifics that provide value.
I have no idea as to why he insists on presenting his "facts" in the
manner that he does. It is such a small thing to provide empirical
data to support them. But that never happens. Perhaps its the electronic
media that tends to exacerbate this. but it really is a problem here.
I know for a fact that there are *many* GEM's that are far more stable
than *any* DOB mount. But I also am very well aware that there are
examples of GEM's that are not more stable. he previously made statements
to the effect "focusing a DOB is more stable than a GEM". Laughable.
Yes it *could* be true given a truely pathetic GEM and a good DOB. But
it is never going to be true in every case. Even given certain price
considerations.
Specifics where his statement could be true would be a Meade LXD500 mount
with an 8" SCT vs a Meade 10" DOB. I know because I had both. The SCT
severely taxed the capabilities of the LXD500 mount. But the DOB also
suffered from this as well. Not as much. But far more than my 10" f/6
mounted on a Parks 1.5" Shaft GEM.
>Jon, it does seem like it could use some clarifying: In your opinion,
>under what conditions (cost, application, operating environment, etc)
>would, say, a 6-inch f/8 Newtonian be more stable on a Dobsonian mount
>than a GEM? Under what conditions would it be equally stable? Less
>stable?
Good idea. And provide only personal details that you yourself have
experienced instead of what you have heard. Personal experience means
more.
Bill
--
William R. Mattil | You're one of those condescending Unix
Sr. System Aministrator | guru's, Here's a nickel kid. Get yourself
(972) 399-4106 | a better computer. - Dilbert
Jon Isaacs
>experienced instead of what you have heard. Personal experience means
>more.
>
>Bill
I am not interested in a fight here. I was discussing my personal experience
with my EQ mounts and my DOB mounts when you jumped in and wanted to re-fight
an old battle.
I am not interested in going over that old ground with someone is who is not
interested in a dialogue.
Jon Isaacs
Mark Elkington
>
> Good question. Tomorrow I will be picking up a 10 inch F5 DOB which I will
> compare with my 8 inch F6 and my 12.5 F4.1, all have essentially the same focal
> length. then I can tell you the answer to your question.. <g>
>
> However the issue here is that the OTA of the 8 inch is only somewhat heavier
> than that of the 6 inch, about 45% I believe, 19 lbs as opposed to 13lbs, both
> very reasonable and the mounts are about the same. However the 10 inch OTAs
> are significantly heavier, over 30 lbs, close to the 3 times that of the 6 inch
> scope. For many this might be a problem.
Hi Jon,
I'd be interested to hear your impressions on your 8" f/6 vs. 10" f/5.
I've asked about these before here (not really procastinating on
buying one or other, just haven't had the time :-).
In particular, what in practice is the extra size and OTA weight of
the 10" like?
How much more structure in DSOs do you see, and what other image
differences are there?
Is coma noticeably worse on the f/5 (at a club night I looked through
a 10" f/5 Guan Sheng i.e. XT10 with 2" eyepice and saw a lot of coma).
Any other impressions etc welcome.
Cheers,
Mark
Jon Isaacs
>
>I'd be interested to hear your impressions on your 8" f/6 vs. 10" f/5.
> I've asked about these before here (not really procastinating on
>buying one or other, just haven't had the time :-).
I have only used the 10 incher a few nights so my impressions are tenative...
>In particular, what in practice is the extra size and OTA weight of
>the 10" like?
>
The 10 incher is definite much larger, but still easy to handle in separate
pieces, not a chore like my 12.5incher, it makes me think first before getting
it out to use.
The 8 incher fits nicely the truck of my Ford Escort, the 10 incher does not
quite make it because of the larger diameter OTA, but it fits on the back seat
nicely.
>How much more structure in DSOs do you see, and what other image
>differences are there?
Definitely the 10 incher is brighter on DSOs, I haven't taken it to dark skies
yet but on Open Clusters and globulars it is certainly brighter.
>Is coma noticeably worse on the f/5 (at a club night I looked through
>a 10" f/5 Guan Sheng i.e. XT10 with 2" eyepice and saw a lot of coma).
There is definitely more Coma but at this time my view it is acceptable, I have
an old 1.25 inch Paracorr. I never use it with the 8 incher, the 10 incher
definitely benefits but it is not a must have like it is with the F4.1 scope.
I haven't tried any 2 inch eyepieces, I don't own any, at large exit pupils I
see lots of flaring.
>Any other impressions etc welcome.
>
>Cheers,
>Mark
If the size of the 10 inch scope is not a problem, I think it is the way to go.
Jon Isaacs
Mark Elkington
Thanks Jon. I've got a club night this weekend so weather permitting
I'll have another look for myself.
Mark