A-P 10" Maksutov-Cassegrain v.s. OGS 10" Ritchey-Chretien
Gregory Santos
I was wondering what your thoughts were on the relative
merits of these two fine instruments. For most amateurs,
this would be an exclusive and once-in-a-lifetime purchase,
so impressions and random comments even from those who have
not experienced either of these OTA's are welcome.
As a start, here are some quick comparisons:
Astro-Physics Mak | Optical Guidance RC
---------------------------------------------
clear aperture | 254mm | 254mm
focal length | 3708mm (f/14.6) | 2286mm (f/9)
% obstruction | 23% | 40%
focuser | moving primary | 2.7" A-P (!)
cooling | active/passive | active/passive
delivery time | ~24 months (?) | ~4 months
cost | ~$10,000 | ~$11,000
weight | ~33 lbs. | ~30 lbs.
length | ~660mm | ~600mm
coatings | 96% reflectivity | standard Al-SiO2*
finish | white textured Al | carbon/magnesium
(silver-gray)**
*other coatings available at additional cost
**white finish available for an additional $2000 (!)
For me, one overriding concern is the long focal length
of the A-P; the OGS has a nice "general purpose" focal
length that seems to strike a balance between image scale
and field of view. Another is the delivery time; A-P
must first grant the privilege of ordering, and then
fabricate, while OGS is geared up to fabricate upon
demand.
Some might have a concern about the 40% obstruction of
the RC design, although the photographs that make it to
S&T, taken through these OTAs, are often exquisite.
Any other thoughts, especially about the relative merits
of the designs (for both visual and photographic use) and
manufacturers?
Ron Wodaski
photographic design -- large central obstruction, but a very large flat
field. The AP scope can be configured for either visual or photography, and
has a much longer focal length (nearly twice that of the RC).
So which one I would choose would vary dramatically with the intended use of
the scope.
--
Ron Wodaski
http://www.newastro.com
"Gregory Santos" <gsa...@syntricity.com> wrote in message
news:3A774BB7...@syntricity.com...
Chris1011
For me, one overriding concern is the long focal length
of the A-P; the OGS has a nice "general purpose" focal
length that seems to strike a balance between image scale
and field of view. >>
One instrument was developed mainly for deep sky imaging, the other for high
contrast planetary. One has a wider field, the other a narrower field (although
either one can be quite easily telecompressed for faster CCD exposures). One
has an open tube with secondary and spider that needs collimation, the other is
a closed tube which is permanently collimated. What's important to you?
Roland Christen
Rockett Crawford
Gregory Santos wrote:
> For me, one overriding concern is the long focal length
> of the A-P; the OGS has a nice "general purpose" focal
> length that seems to strike a balance between image scale
> and field of view.
> Another is the delivery time; A-P
> must first grant the privilege of ordering, and then
> fabricate, while OGS is geared up to fabricate upon
> demand.
>
> Some might have a concern about the 40% obstruction of
> the RC design, although the photographs that make it to
> S&T, taken through these OTAs, are often exquisite.
>
> Any other thoughts, especially about the relative merits
> of the designs (for both visual and photographic use) and
> manufacturers?
Just wanted to mention that I think Roland said that he
has a focal reducer that brings his scope down to f/8.
Rockett Crawford
----------------------------------------------------------------------------
Capella's Observatory (CCD Imaging)
http://web2.airmail.net/capella
Del Johnson
mirror separation is very critical, and that the wide corrected field
only works if one uses a field flattener (or curved film). The Ritchey-
Chretien's that I have used have been disappointing on the planets.
Del Johnson
In article <20010130192238...@ng-md1.aol.com>,
Sent via Deja.com
http://www.deja.com/
Michael Richmann
of the focal plane of the Star Instruments mirror set (chosen as a
typical example since it's installed in both RCOS and OGS scopes) is a
steep 14-15".
As long as you're willing to live with that or spend the money on a
field flattener, the R-C design otherwise is essentially flawless (no
coma, etc.).
---
Mike
http://www.concentric.net/~richmann/
WHALEN44
Apples and oranges. Having looked through both designs, I would pick the MCT
for visual observing.
Richard Whalen
whal...@aol.com
"Time spent observing the heavens is not deducted from your lifespan"
ar...@selena.kherson.ua
Roland,
I think you don't have to explain something. This guy try a troll.
It is obvious that HE does understand enough to make his own
choise. He does understand the principal difference beteen these
oppositely purposed scopes.
Briefly - the choise is depends of a main interest in astronomy
(or balance of some interests). There is no perfect scope for each
purpose. All peoples, who can afford and wish to buy any of these
instrument ALREADY know enough about their difference and will
always make a right choice.
I can repeat - THIS IS A TROLL.
Valery Deryuzhin.
ARIES.
JMc
definitely pushes it towards visual observing and away from any photo or
CCD work - the opposite of all the other scopes AP sells. Perhaps the
small obstruction and secondary on the corrector forced the design into
that corner. Jay Freeman's comments about the secondary baffling (or
lack thereof) indicate to me that the design might be a little bit too
optimized <g>.
Jim McSheehy
Rockett Crawford
JMc wrote:
> I've often wondered about the f/15 design for AP's Mak because it
> definitely pushes it towards visual observing and away from any photo or
> CCD work - the opposite of all the other scopes AP sells. Perhaps the
> small obstruction and secondary on the corrector forced the design into
> that corner. Jay Freeman's comments about the secondary baffling (or
> lack thereof) indicate to me that the design might be a little bit too
> optimized <g>.
IIRC there is an f/8 reducer that would make the AP Mak an
excellent CCD imaging scope for a medium to large pixel sized
camera IMHO.
Chris1011
I've often wondered about the f/15 design for AP's Mak because it
definitely pushes it towards visual observing and away from any photo or
CCD work - >>
Any CCD work? That's a bit harsh. Take a look at the Ring Nebula on our web
site and then tell me about suitability for imaging. And you certainly are
totally in the dark when it comes to baffling. In fact, it sounds like it has
you baffled.
Roland Christen
Herm
then you will take the time to learn how to collimate it..hint: think of an f2
newt and how easy that is to collimate. I would consider these instruments not
to be portable due to the collimation issue, but once collimated they are superb
imaging instruments.
On Wed, 31 Jan 2001 01:59:46 GMT, Del Johnson <deljo...@my-deja.com> wrote:
>I might add that collimating a Ritchey-Chretien is difficult as the
>mirror separation is very critical, and that the wide corrected field
>only works if one uses a field flattener (or curved film). The Ritchey-
>Chretien's that I have used have been disappointing on the planets.
>
>Del Johnson
Herm
Astropics http://home.att.net/~hermperez
Ron Wodaski
right it does include a fancy-shmancy flattener.
However, I had thought that the big advantage of the RC design was the flat
field for film, so I guess I was wrong about that. I'll have to do a little
more homework on it.
--
Ron Wodaski
http://www.newastro.com
"Michael Richmann" <rich...@concentric.net> wrote in message
news:3A777B96...@concentric.net...
JMc
wonderful - the best stuff I've ever seen from an f/15 scope.
Baffled? The part I read says:
"A consequence of small obstruction is poor baffling: Sky light sneaks past
the obstruction, down the baffle tube, to the field. The aluminized
spot of
this design is sufficient for a half-inch diameter field, and a
removable, larger
disc attaches to the center of the corrector to allow full baffling of a
larger
field. Wide fields are useful only at low magnifications, or for
imaging, and in
such circumstances the contrast improvement for fine detail is
undetectable, so the
larger baffle will not hurt when the telescope is so used."
You can attack me all you want, but that is what one of your MCT
customers, an experienced observer, had to say about the baffle design.
I have enough book learnin' to know that geometric optics is a
convenient fiction, and there will be scattered light inside the
theoretical shadow cast by any baffle. Can a baffle be too big? Yes, and
contrast will suffer. Can it be too small? Show us a daytime photo taken
with your MCT @ 23% CO.
Jim McSheehy
ar...@selena.kherson.ua
JMc <tri...@my-deja.com> wrote:
>Can a baffle be too big? Yes, and
> contrast will suffer. Can it be too small? Show us a daytime photo taken
> with your MCT @ 23% CO.
>
> Jim McSheehy
Jim,
This scope wasn't designed for a daytime shooting.
You know well, I believe, what does it mean a S/N
ratio. At night observing small baffle is quite good
for high resolution observing without any impact from
illusive "scattering light" from the baffles etc.
For daytime, one can use a larger screen baffle and
all will be same OK as in standard MCT .
So, no question at all. Only if you like to spend your
free time for an empty discussions. All is well minded
in these AP and our ARIES analog scopes. You better
need to take a look through one of them on Jupiter under
good, not even say under excellent seeing.
JMc
The AP Mak is a wonderful scope, but like the Synta refractors, an
accessory or two could help make it legendary. How about a Bafflecorr?
It would sense the illumination in front of the corrector and
automatically expand to the correct CO. Or, AP could offer a new
focuser, exclusive to the MCT - one with a 0.965" ID <g>.
Jim McSheehy
John J. Kasianowicz
JMc wrote:
[snip]
> I have enough book learnin' to know that geometric optics is a
> convenient fiction, and there will be scattered light inside the
> theoretical shadow cast by any baffle. Can a baffle be too big? Yes, and
> contrast will suffer. Can it be too small? Show us a daytime photo taken
> with your MCT @ 23% CO.
Do you mean an image of a planet or a terrestial object taken during
daylight hours?
ar...@selena.kherson.ua
JMc <tri...@my-deja.com> wrote:
> Hi Valery,
>
> The AP Mak is a wonderful scope, but like the Synta refractors, an
> accessory or two could help make it legendary. How about a Bafflecorr?
> It would sense the illumination in front of the corrector and
> automatically expand to the correct CO. Or, AP could offer a new
> focuser, exclusive to the MCT - one with a 0.965" ID <g>.
>
> Jim McSheehy
Hi Jim,
We already have a manually driven baflle-corr . :-)
The AP has two stage one, we - four stage one.
This is a kit of three quickly excgangeable screens.
It took about 5 sec to exchange them.
Valery Deryuzhin.
Chris1011
convenient fiction, and there will be scattered light inside the
theoretical shadow cast by any baffle.>>
Unless a front obstruction is 100%, there will be light coming in from oblique
angles to illuminate any and all internal baffle tubes. This occurs in all
Cassegrain designs including all commercial SCTs, and yet they still work fine.
Your above statements convince me you are clueless about Cassegrain baffles.
And I am too busy to try to educate you now.
Roland Christen
JMc
you get some free time:
Jim McSheehy
Adrian Catterall
look in clear skies early this evening, although it soon clouded over. I
haven't mounted it properly on a decent mount yet, so used an ordinary
tripod. I used a Meade 40mm plossl to center, then a Tak LE 12.5mm,
followed by a 6mm and 4mm radian, all of which are good eyepieces as
used with my 5 inch AP refractor.
Viewing Castor, Pollux, Aldeberan, jupiter and the moon revealed quite
appalling chromatic aberration, which was easily apparent in focus with
violet colours on one limb of jupiter and green on the other. Similar
results with the mentioned stars. There was a little spherical
aberration, but very mild.
Interestingly Markus Ludes was at the UK astrofest this weekend and we
tested two Sky90's on light bulbs - mine seemed okay and another display
model showed significantly more spherical aberration!
My question is should I stick by Tak Sky90's, or abandon them all
together? There have been a few reports of quite good ones on this
list..
Personally I blame Roland Christen, as this is a stop gap scope until my
AP traveler arrives :-)) I think I may speak to Markus about a 4 inch
TMB scope?
Adrian
Adrian Catterall, CCD astronomer
email: Catt...@observatory.demon.co.uk
Visit my Web page at: http://www.observatory.demon.co.uk
Guilden Morden
Hertfordshire
U.K.
richardan...@my-deja.com
cover a 35mm or larger film plane without distortion? I thought
one of the good things (provided you aren't using a 4kx4k ccd)
about CCD imaging is that because of the small size, you can use
lenses that wouldn't be suitable for film work owing to their small
area of good correction, hence the scope should be cheaper and maybe
alot faster?
-Rich
In article <3A782C7E...@Audiotel.com>,
Rockett Crawford
richardan...@my-deja.com wrote:
> If someone wanted a scope for CCD work, is it required the scope
> cover a 35mm or larger film plane without distortion? I thought
> one of the good things (provided you aren't using a 4kx4k ccd)
> about CCD imaging is that because of the small size, you can use
> lenses that wouldn't be suitable for film work owing to their small
> area of good correction, hence the scope should be cheaper and maybe
> alot faster?
That's true. An SCT will show a lot of edge distortion
in a 35mm frame because of it's field curvature and most
CCD chips take a much smaller cross section of this curved
field. Offsetting this somewhat is the way CCD images
are presented as opposed to film. Because CCD images
do cover a smaller area, they tend to get enlarged in the
final product to present a similar sized image to film
and any distortions tend to look more obvious.
One of the things that makes my CCD imaging experience
work well with my SCT is because field flatteners can be
made to work well with small cross sections and at fast
f/ratios so the smaller cross section is even flatter
(example Optec's f/5 widefield).
I would prefer a higher quality scope such as the AP Mak
or a 10 inch Mak-Newt, but at 10 grand, both are out of my
budget range at the moment.
Rockett Crawford
----------------------------------------------------------------------------
David A. Novoselsky
received a bad scope from Tak or AP or Tom Back, or any mfg. I would return
it. I am not in the United Kingdom, so I do not know who is the Tak
distributor there. However, in the United States, I know that the US
distributor -- TNR-- has told me that if I ever have a problem with a Tak
scope or mount, they will take care of the problem. I have a Sky 90 and
have not experienced the problems you note. I have read Todd Gross'
updated reports and he is happy with his. I have 'heard' from many here in
the US who share my liking for this scope. If you got a bad one, ask them
to replace it. I would be shocked if the answer was no, being a multiple
Tak owner now and having owned several others in the past. Dave
Chris1011
Personally I blame Roland Christen, as this is a stop gap scope until my
AP traveler arrives :-))>>
Ouch! It's not my fault. I didn't know you had one on order.
Roland Christen
Steve Wright
same problem. Todd Gross had problems with his first two FSQ's, the
third was fine. Could this be initial production QA problems. If I
remember correctly the serial number of the unit on display at astrofest
was 58.
Steve.
In article <3A7F0EBE...@ix.netcom.com>, "David A. Novoselsky"
<DN...@ix.netcom.com> writes
--
Steve Wright
Kevin & Monika
> Ouch! It's not my fault. I didn't know you had one on order.
>
> Roland Christen
Damn glad to hear it, you should be busy building my AP900GOTO, and not
wasting time checking waiting lists for Adrians scopes :-)
Bye for now
Kevin
kevs...@globalnet.co.uk
www.kevsmith.com
Supported by www.metprep.co.uk and www.archive4images.com Market leaders in
Scientific Imaging Systems
Toddwx
Actually, one of the things I liked best about that old Stowaway was the
focuser, the tube itself may have been slightly smaller (less diamter) than
the Sky90 in retrospect too, making it a tad easier to carry
Dave Novoselsky
what. I am confused by this 'the Stowaway is" stuff. I sounds like a
marvelous scope, but Roland decided to stop making them and they rarely turn
up on the secondary market. Would a new AP in the 90 mm size and the
overall size of the Sky 90 sell? Sure, Allister St. Claire and I decided
that the visual performance of the Sky 90 was so close to that of a 4" scope
that the benefits of overall size and ease of use made it the clear winner
over a 4" for all but the most demanding planetary/lunar -- and then on
nights of exceptionally good seeing. So if AP re-introduced the Stowaway
or a variation on that theme would it sell like hotcakes? Yes, but then at
the expense of production of the other AP scopes as Roland can only make so
many scopes a year. So then Traveler, 130 and 155 production slows. So, I
say, while the Stowaway sounds marvelous, it can't be had for a reasonable
price today, Roland isn't making them, so that leaves us with ---- oh yes,
the Sky 90 which many of us are very pleased with. Dave
"Toddwx" <tod...@aol.com> wrote in message
news:20010207065756...@ng-fi1.aol.com...
John J. Kasianowicz
I'm not sure what you're confused about. The StowAway is a high quality,
portable and therefore highly desirable OTA. Rumour had it that Roland might
produce a longer focal length version of the StowAway. While that might
increase the scope's performance a bit, the portability of the "production"
92mm StowAway seems ideal for a travel scope.
While I'm sure I'd enjoy using the Tak Sky90 (_please_ feel free to send me
yours, with the 8" TMB as a finder), and I may end up getting one, I am
comfortable with the optical and mechanical qualities of Roland's scopes.
In reply to Todd Gross, Dave Novoselsky wrote:
> And my TV-140 is smaller than the AP-130, faster and has more aperture.
So
> what. I am confused by this 'the Stowaway is" stuff. I sounds like a
> marvelous scope, but Roland decided to stop making them and they rarely
turn
> up on the secondary market. Would a new AP in the 90 mm size and the
> overall size of the Sky 90 sell? Sure, Allister St. Claire and I decided
> that the visual performance of the Sky 90 was so close to that of a 4"
scope
> that the benefits of overall size and ease of use made it the clear winner
> over a 4" for all but the most demanding planetary/lunar -- and then on
> nights of exceptionally good seeing. So if AP re-introduced the Stowaway
> or a variation on that theme would it sell like hotcakes? Yes, but then
at
> the expense of production of the other AP scopes as Roland can only make
so
> many scopes a year. So then Traveler, 130 and 155 production slows. So, I
> say, while the Stowaway sounds marvelous, it can't be had for a reasonable
> price today, Roland isn't making them, so that leaves us with ---- oh yes,
> the Sky 90 which many of us are very pleased with. Dave
John J. Kasianowicz
Yerkes refractor you are considering ...
Dave Novoselsky wrote:
in message news:Z6bg6.10525$Fq4.1...@typhoon.mw.mediaone.net...
> And my TV-140 is smaller than the AP-130, faster and has more aperture.
So
> what. I am confused by this 'the Stowaway is" stuff
[snip]
Rich N.
Rich
Toddwx wrote in message <20010206205549...@ng-ch1.aol.com>...
>adjustable inside only, requires factory
Rich N.
Dave Novoselsky wrote in message ...
>And my TV-140 is smaller than the AP-130, faster and has more aperture. So
>what. I am confused by this 'the Stowaway is" stuff. I sounds like a
>marvelous scope, but Roland decided to stop making them and they rarely
turn
I believe Roland stopped making them because he had only
60 fluorite blanks. The blanks came from Baader. Baader got
the blanks from Zeiss when Zeiss closed their amateur
astro division. Roland, please correct me if I'm wrong.
The original Stowaway certainly performs extremely well. I find
I use it much more than I ever thought I would.
If AP starts making them again, I wouldn't mind if AP makes
the new Stowaway with about the same focal length as the Traveler.
This would give the Stoaway a focal ratio about f/6.5. With FPL53
it should have excellent color correction at that focal ratio. It would
weigh only a couple of ounces more than the original. It would also
be nice if it had a tube something like a TV tube ring. This would
allow for easier balancing and it would let you easily rotate the tube
without tools.
But, I would guess with so much demand for the larger APs
Roland may not have much time for a new project.
Rich
Toddwx
japan, that is a negative, yes.
They are very good at swapping out though in my experience if there is a
problem
tg
ps.. sam ewiht the fsq106
Rich N.
scope. I've had good support from TNR. It makes
me feel much better about buying their products.
Rich