Quality of coulter optical mirrors
Juergen Stadler
i want to build a 12.5`` or 13´´ newton telescope and already have a parks
12,5´´ tube. I now found at the coulter optical HP a 13.1´´ primary mirror
at an affordable price. Can anyone tell me something about the optical
quality of these mirrors or does someone know other manufactures of mirrors
with good quality which ship overseas to germany?
Greetings
Jürgen
p.S. Please apologize if there´s something not correctly spelled but my time
at school is a lot of years behind.
starlord
--
The year is 2261 ... The Place is Babylon 5
www.starlords.org
"Juergen Stadler" <juergen...@degnet.de> wrote in message
news:94ihiv$dierq$1...@fu-berlin.de...
Juergen Stadler
"starlord" <star...@qnet.com> schrieb im Newsbeitrag
news:3a6dab84$1...@news.qnet.com...
> how you going to fit a 13.1in mirror into a 12.5in tube?
I´ll wash it very hot so it shrinks to 12.5 :-).
No, the tube´s ID is 405 mm (15 7/8``) and is designed to fit the 12.5´´
parks mirror.
John Afdem
resale value because their optics were top of the line in their day.
"Juergen Stadler" <juergen...@degnet.de> wrote in message
news:94kdfl$dt5v1$1...@fu-berlin.de...
David W. Knisely
> Coulter's are generally regarded well. Used coulter dobs hold a strong
> resale value because their optics were top of the line in their day.
>
Well, in reality, the old Coulter was almost never considered "top of
the line". They put out fairly good optics consistently (but *very*
slowly) in its early years (prior to 1977), as after that (mostly when
they started mass-producing their Odyssey line of Dobs), they started to
go downhill. Just prior to their disappearance, their quality control
was all over the map. My current ten inch was a Coulter mirror, and it
was horrid, with a *very* rough dog-biscut surface and overall
correction not even 70% of what it should have been for minimal
quality. I had to get it refigured by Enterprise Optics, who did a very
good job getting it to about 1/20th wave. I would have to look long and
hard at a used Coulter before I would even consider buying one. Clear
skies to you.
--
David Knisely KA0...@navix.net
Prairie Astronomy Club, Inc. http://www.4w.com/pac
Hyde Memorial Observatory, http://www.blackstarpress.com/arin/hyde
***********************************************
* Attend the 8th Annual NEBRASKA STAR PARTY *
* July 14-20, 2001 *
* http://www.nebraskastarparty.org *
***********************************************
John Afdem
While there are exceptions to every generality, the generality is NOT
disproved by the existance of an exception.
Generally, Coulters are well regarded.
For owners reviews and ratings:
http://www.excelsis.com/vote/astro/telescopes/index.html
For a review that summarizes the Coulter 13.1 as 'recommended' while banging
them a bit:
http://www.scopereviews.com/page1b.html#7 and their rankings page
http://www.scopereviews.com/matrix.html
Now just because a mirror is made by a generally well-regarded manufacturer
doesn't mean that everyone gets a great mirror (David can witness to that,
having bought a bad one)
So get someone who's better at buying mirrors than David to check the mirror
(any mirror) before you buy it. Also, you should always check the Astromart
classified on something like that to see if there are some comparables you
can refer to so you know the price is right:
http://63.169.124.5/cats.asp
Regards,
John Afdem
(David: I just could NOT resist ;-)
"David W. Knisely" <KA0...@navix.net> wrote in message
news:3A6E67...@navix.net...
David W. Knisely
> Such is the problem with anecdotal evidence, it's all over the map.
>
> While there are exceptions to every generality, the generality is NOT
> disproved by the existance of an exception.
>
Well, my experience isn't exactly anecotal, as it is based on about 30
years of telescope experience, both personally, and with other
amateurs. I have a very good 8 inch f/7 Coulter mirror which is
probably at least 1/10th wave, and which dates back to about 1972 (but
it isn't the "1/25th wave" Coulter was claiming). However, we have had
a number of ten and 13 inch Odysseys in our club which have somewhat
variable or even rather questionable mirror quality, although at the
price, they were considered "bargans" at the time. There were some
which were good, but some which were not, so it wasn't just one or two
mirrors. Anyone who made the rounds of the various Astronomical League
regional conventions could see this sort of quality variation as well in
some of the instruments people were using there which contained Coulter
mirrors. The opinions of those Coulter owners were basically that they
were often "OK", but not "top of the line" (and more importantly, there
was a more than minimal chance of getting a mirror which was a real
dog). The major talking point of the Coulter optics was how relatively
inexpensive they were for the accuracy they "claimed". 1/25th wave can
be interpreted many ways, and Coulter played a bit fast and loose with
this figure. My 8 inch f/7 could have been 1/25th wave *on the surface*
but NOT on the wavefront (wavefront error would be about 1/12.5 wave).
Wavefront error has been the standard, with the often cited "1/4 wave"
Rayleigh criterion being applied to the wavefront and *not* to the
surface. Many of the later Coulters had figures which were barely a
quarter wave on the wavefront (or frequently a little worse), and most
of these date to the early 1980's or later. Again, once aperture fever
ignited the Dosonian rush in the 1980's, the quality of the mirrors we
saw in the Odysseys began to go down. Comparative reviews done by Sky
and Telescope of several ten inch mirrors clearly showed that Coulter
was not "top of the line" (a Parks mirror was considered the best).
> Now just because a mirror is made by a generally well-regarded
> manufacturer doesn't mean that everyone gets a great mirror (David can
> witness to that, having bought a bad one)
>
> So get someone who's better at buying mirrors than David to check the
> mirror (any mirror) before you buy it. Also, you should always check
> the Astromart classified on something like that to see if there are
> some comparables you can refer to so you know the price is right:
Telescope mirrors can be tough to judge accurately, even with the star
test. The ten inch Coulter mirror I bought in 1985 came in a scope
which was built by a former club member, and he had glued the ENTIRE
mirror to the back of his primative plywood mirror cell! Needless to
say, it had some visible spherical aberration in the star test, a fact
that I mistakenly attributed to the glue inducing stress at the cold
temperatures I was testing the scope in. At low to moderate powers, it
seemed to perform fairly well, so I made the mistake of buying the scope
for $400 with the expectation of rebuilding the whole thing. Once I got
the mirror 'unstuck' and into a rebuilt cell, the problem actually got a
bit worse! I quickly learned how to do mirror bench testing with the
Caustic test and found to my horror that the mirror was just awful. In
the center of the mirror was a nice fat crater complete with central
peak and secondary pits all around it ("dog-biscuts"). It was far from
the dubious "1/25th wave" which Coulter had been advertising at the
time. Its overall curve seemed to resemble that of two mirrors of
slightly different focal lengths which were fused together at the 70%
zone. Needless to say, I had it refigured promptly at Enterprise, and I
was more than satisified at the results (1/20th wave on the wavefront
confirmed on my tester). I suppose at least that Coulter could be
thanked for using Pyrex and removing enough glass to make Enterprise's
task a bit easier than starting from scratch, but as for their quality
control, Coulter left something be desired. As for buying them on
Astromart, I would NEVER buy an old Coulter sight unseen. You might get
an acceptable one, but then again, you could end up like I did with a
dog. It might be better to try for a current Odyssey scope from the
"New Coulter", a division of Murnaghan Instruments, rather than buying a
shot in the dark from the past. Clear skies to you.
John Afdem
the case may be) doth protest too much.
I must say I find it humorous that you protest that your anecdotal evidence
was described as anecdotal and then defend it with yet more anecdotal
evidence. But be that as it may.
You've obviously run into trouble with the phrase 'top of the line'. A
'line' of cars, is not every car ever made. If an olds dealer said that a
model of olds was 'top of the line' than you certainly would be remiss to
try to compare it with a Rolls. Which is exactly what you're doing comparing
a Coulter with a Parks (Given that a Parks costs GOBS more money..... seem
to make very few mid priced large dobs)
This is unless you're serious about comparing Parks, who currently sell
reflectors like an 800 dollar 4.5 inch, and a 1300 dollar six inch, to say
nothing of a 7000 dollar 12.5 , to the Coulters and Meades of the world. But
you couldn't be serious about that, could you? (18,000 dollar 16 inchers!!
Yep, lets measure all scopes by that standard.)
Oh, and I did not suggest that anyone buy anything 'sight unseen' from
Astromart. Those were your words, not mine. I suggested that Astromart might
be a good place to check for comparable prices.
While you may well have been going to star parties and pursuing this hobby
for 30 years, I honestly wonder at what point in time you stopped being
reasonable and helpful and became a pedantic and irritating curmudgeon. If
you're that way in person your star parties must be a real joy indeed! Do
you check all the scopes at the door to see that they pass your 1/25th wave
test of acceptablity? How fun!
Back to the point at hand. The gentleman asked about Coulter mirrors
reputation. As I stated what seems like weeks of pedantic carping ago, the
Coulter brand is well respected. Now earlier I stated that they were
considered 'top of the line'. Although Coulter is still often used for
comparisons with newer large dobs (they're that good), I now stand corrected
and must qualify my statement that they are 'top of the line' by noting that
they sometimes aren't as good as scopes costing ten times as much.
We happy now?
Regards,
John Afdem
"David W. Knisely" <KA0...@navix.net> wrote in message
news:3A6E95...@navix.net...
David W. Knisely
> You've obviously run into trouble with the phrase 'top of the line'. A
> 'line' of cars, is not every car ever made. If an olds dealer said that
> a model of olds was 'top of the line' than you certainly would be
> remiss to try to compare it with a Rolls. Which is exactly what you're
> doing comparing a Coulter with a Parks (Given that a Parks costs GOBS
> more money..... seem to make very few mid priced large dobs)
>
You are the one who seems to be having the jargon problems (it was
clearly a poor choice of words on you part). "Top of the Line" means
the best model that is produced in the line of models of cars a
manufacturer produces. For telescopes, top of the line means something
that is at least close the best *quality optics* that is available.
This was not quite true of Coulter (at least, not consistently and not
later on in their existance). They essentually had only one line: their
Odyssey Dobsonians. They made the "Yugos" of the telescope world. For
just the optics (which is what Coulter started out making), in terms of
mirror costs, at the time of production, the Parks and Meade 10 inch
*mirrors* (rememeber we are ONLY talking about mirrors this time) were
running around $400 or so, as were the Edmund mirrors. The Coulters
were about $300, so they were cheaper, but their accuracy claims of
1/25th wave were somewhat bogus, as at least initially, they were never
qualified as to what they meant. It doesn't matter what Parks is doing
*now* or what kind of scope they are currently building around their
optics. All it matters is that *at the time* Parks mirrors were
compared with Coulter, and they beat Coulter's quality. This shows that
Coulter was *not* "top of the line".
It isn't anecdotal evidence that I measured my mirror and found it
wanting. It isn't anecdotal evidence that Sky and Telescope tested
random samples of these mirrors and found that Coulter wasn't the best.
It isn't anecdotal evidence that I have looked through more than a few
Coulters and found their optics basically passable or worse. These are
facts. There are good relatively inexpensive Dobsonians with equal or
better quality currently on the market today than with some of the
older Coulter dobs, which were definitely the "Yugos" of the telescope
world. They were very hard to collimate accurately, had simple helical
focusers with horrid play (most amateurs who got them quickly replaced
the focuser with something cobbled together in their workshops), and had
a secondary support vane which was horridly thick (BIG diffraction
spike). The optics were often passable, but were glued down to their
simple supports, often inducing stress into the glass which caused
peformance problems. In other words, NOT TOP OF THE LINE: Does this
mean that a person who is offered a Coulter Dob for a reasonable price
should turn it down? Of course not. With some inspection, it might
prove to be a useful instrument with potential for modification and
improvement (ie: a "fixer-uper"). However, when buying an older Coulter
scope, the best advice is to look it over carefully before laying out
the cash. Personally, I would rather pay just a little more and get
something somewhat more usable. Clear skies to you.
Pafralio
so be it. He seems to have a lot of it.
John Afdem
I can't argue with that!
"Pafralio" <pafr...@aol.com> wrote in message
news:20010124220525...@ng-xa1.aol.com...
John Afdem
You're on a roll
"David W. Knisely" <KA0...@navix.net> wrote in message
news:3A6F3F...@navix.net...
Mike Simmons
I haven't seen anything from you that adds to the discussion. How many
older Coulter mirrors have you checked out? Any experience at all that
would help here? You give some references to other peoples' experiences
(anecdotal data) but you apparently haven't even read them since they
are new reviews and therefore not relevant to this thread. What makes
the individual user reviews you quote more useful than David's? Do you
have any relevant information or experience of your own? If not, come
on back when you've solved your emotional problems and have something
useful to add.
Mike Simmons
John Afdem
it's SO meaningful.
I think if you'll review the USER ratings I posted and the REVIEWS I posted,
you'll find plentiful evidence to support my assertion that Coulter products
are generally quite well respected.
"Mike Simmons" <ecli...@mwoa.org> wrote in message
news:3A6FE939...@mwoa.org...
David W. Knisely
> I think if you'll review the USER ratings I posted and the REVIEWS I
> posted, you'll find plentiful evidence to support my assertion that
> Coulter products are generally quite well respected.
>
Maybe respected *NOW* by some, but NOT back a few years. Coulter
Optical (Idyllwild, California) was bought out a few years ago by
MURNAGHAN INSTRUMENTS (West Palm Beach, Florida). They bought the
rights to produce the Odyssey line, and are currently doing so, making a
few improvements in the instruments, but otherwise changing the look of
the design very little. The reviews you cite are for CURRENT Coulter
instruments, and point to the obvious problems with the present models,
so the reports aren't quite as glowing as you picture them. The
so-called "ratings' from the other website you cite are from just a
handfull of users, a number which is NOT statistically significant (and
they refer to the CURRENT Coulter/Murnaghan scopes, NOT the ones
produced when Coulter was in business for itself). In any case, the
scopes and optics of the ORIGINAL Coulter Optical a little before they
were bought out by Murnaghan were not considered TOP OF THE LINE. As
the previous poster indicated, you have failed to put up significant
evidence to support your contention that Coulter "in their day" WAS
considered "Top of the Line". One review and a handfull of ratings of
CURRENT Coulter instruments does not count!! There is nothing currently
terribly wrong with CURRENT Coulter products, as they represent some
value for the money, but this was not true a few years ago. Your other
posting to the other respondent's comments (ie: "Yes, he is full of it")
clearly shows that you are the one who is full of it.
John Afdem
protest to much'.
The simple fact, supported by independant reviews and user comments I
posted, is that my opinion that Coulters are generally well respected
equipment is correct. On the other hand, you've posted nothing but your
opinion based upon your own anecdotal experience. Given the time that's
passed on this thread, which SHOULD have provided you with ample opportunity
to provide urls to independent support for your view, if it existed, I can
only conclude that you've tried and failed to find such support. Either that
or your ego won't permit you to consider that your opinions and anecdotal
experiences are not the end-all of astronomical equipment evaluations.
I rest my case.
"David W. Knisely" <KA0...@navix.net> wrote in message
news:3A7083...@navix.net...
Mike Simmons
this time because you've been told this several times -- it's not
relevant to the discussion of older Coulter optics. It's useless
information in this discussion. What you are offering is second-hand
anecdotal evidence on a different company.
One of your URL's is a single single experience with Coulter as opposed
to David's multiple experiences over years. You are apparently one of
those that thinks that anything on a web page must be correct. It used
to be that dumb people believed anything they saw in print. The
newspapers have been replaced by the Internet for those unable to
evaluate evidence for themselves. "Yes, Virginia, there is a Santa
Claus."
Do you have any experience with Coulter optics? Anything of your own to
"add to the discussion" or something "meaningful" to "insert"? You've
added nothing new so far. Have you ever actually looked through a
telescope (Coulter in particular) or do you just read about it.
Hey, David, looks like you caught another boy with more time than
brains.
John Afdem
The bottom line here is that the anecdotal advice of a curmudgeon is worth
about as much as Bill Clinton's 'I did not have sex....'
STILL waiting for the curmudgeon to come up with even a smidgen of
independent verification for his views. Ditto's for you.
"Mike Simmons" <ecli...@mwoa.org> wrote in message
news:3A709F2D...@mwoa.org...
David W. Knisely
> Hey, David, looks like you caught another boy with more time than
> brains.
Well, I would probably not say that exactly, but it is fairly clear that
he seems to lack something in the experience end of things. He doesn't
seem to have carefully read even his own Internet sources, to say
nothing of understanding what exactly we are trying to say (ie: that
people should watch out for *some* of the older original Coulter Dobs).
When he finally resorted to insults and condescending talk, it was
obvious that he had little of substance to offer. That "voting" site he
cited is particularly telling, since the rating (8.0) is based on *only*
4 people's votes! (and even then, its for the *New* Murnaghan Coulter
and not the original telescope). He should have read some of the
comments in those votes, as well as Ed Ting's review of the "original"
red-tube Coulter. Despite "recommending" it (which is not even to close
to the top of his rating scheme), much of Ed Ting's review of the 13" is
particularly pointed:
> First, the bad news: The optics are loaded with coma. Astigmatism is
> visible even when the stars are "in focus." The azimuth bearings are
> too tight, and the rocker box, made of cheap chip-board, looks as if
> it's going to disintigrate at any moment.
(Gad, that was even worse than my Coulter ten inch mirror was!!).
Ting then goes on to say....
> The name "Coulter" is synonymous with cheap, large telescopes; the
> company is generally credited with starting the modern Dobsonian
> revolution. Coulter buyers know what they're getting into, and don't
> expect cutting-edge optical design.
and even more pointed comments....
> These telescopes will never be considered heirlooms, but Coulter
> doesn't exactly help its cause, either. For example, in late 1995,
> customers sending $395 to the company could buy the "Odyssey 8 Combo,"
> which consisted of the rocker box, a 27 mm eyepiece, and TWO 8" optical
> tube assemblies -- an f/4.5 and an f/8 unit. And regarding that 27 mm
> eyepiece. Well...let's just say that I'm curious as to how many
> surplus binoculars gave their lives to the Coulter company.
Ah, and he forgot to mention just how *long* many of us had to wait just
to get these scopes after the excuses like "its in the coating room", or
"it just went to shipping" (month after month). When we did our first
telescope making class in our club, it got delayed mostly due to the
long wait and unknown delivery times for the optics. Oh well, at least
the mirrors were cheap! Ting goes on to say....
> The model tested here is one of the red-tube "Coulter" units. The
> early Coulter models were blue-tubed, and were squared-off on the lower
> half of their tubes. The blue-tube units had a horrible mirror cell,
> just a piece of rope that held the mirror in place like a sling. You
> had to insert and remove the mirror before and after every observing
> session.
>
> A newer series, with a red tube (not squared-off) appeared some time
> later. The red-tube units had a permanent (even adjustable!) mirror
> cell, but the focuser was just a piece of plumbing with a locking ring.
> This "focuser" drove me mad as I tried to focus M13 in my 7 mm Nagler.
Glad he mentioned that focuser. It drove a friend of mine mad too when
he brought his 8 inch Coulter to me for collimation. He had tried to
use his laser collimator in it and couldn't due to the horrible play in
that "plumbing" focuser. We tried for over an hour to get the darn
laser lined up (weighed as much as a Nagler), but in the end, I just got
the collimation as close as I could with just my sight tube and let him
take the scope home. It works after a fashion, but its far from "top of
the line". I have used the old Odysseys (8 inch, 10 inch, 13.1 inch and
a real "monster" of a 17.5 inch), and all seem to have most of the same
basic problems. However, they were at least relatively inexpensive, and
if you got one with halfway decent optics, you had something which could
be "rebuilt" into a more usable scope. At least with the "new" Coulter,
things have gotten a bit more honest, as they cite a 1/8th wave surface
accuracy, which, if true, should be enough to yield reasonably good
performance. However, I still hate the way that secondary holder and
thick "single-vane" spider work (or 'doesn't' work). It is this fact
(along with the focuser) that makes me recommend some of the Orion or
Meade Dobs over Coulter's Odysseys. Clear skies to you.
Mike Simmons
>
> Time for you two to end your circle jerk and come out and smell the roses.
> The bottom line here is that the anecdotal advice of a curmudgeon is worth
> about as much as Bill Clinton's 'I did not have sex....'
Do you know of any other advice that's available? There's been nothing
else presented in this thread about older Coulter mirrors. Just a few
anecdotes about mirrors made by a different company with the Coulter
label. BTW, do you know those people well enough to trust their
anecdotes?
> STILL waiting for the curmudgeon to come up with even a smidgen of
> independent verification for his views.
There hasn't been a "smidgen" of evidence from you but I don't think
anyone is waiting for it. You seem pretty smidgenless on older Coulter
stuff. Yep, pretty unsmidgified.
>Ditto's for you.
Uh, what views of mine do you want verified? I didn't say anything
about the quality of Coulter optics, so what views of mine are you
referring to?
I didn't think you'd answer the questions about your own experience in
astronomy in general or Coulter optics in particular. Hmm, nothing to
add, knocking other posters, starting off with insults and calling
people names (you used the word "curmudgeon" twice in one post!), no
evidence to present, no experience... I wonder why you're here? HEY,
you wouldn't just be trying to <gasp> inflame people, would you?
Mike Simmons
Larry Robinson
ten years and used it tobserve the Herschel 400 list. It works great
on faint deep sky objects, but is not as good on planets and double
stars. I would say most of the problem is due to coma. But I bought
it to observe faint deepsky objects and it works well for this.
The 17.5" is much better. The problem with it is weight. It is a
monster to set up.
Larry Robinson
Olathe KS
Bob Branon
( Meade) and an ETX 125, so I do have other scopes to compare it with.....
"Larry Robinson" <lrob...@ix.netcom.com> wrote in message
news:vka87t8mo397heag5...@4ax.com...