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Questar 7 optics tested

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#1 Erik Bakker

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Posted 01 October 2009 - 03:15 AM

Last week I had my Questar 7 tested by master optician Hans Dekker at Opticon. After some fiddling with the OTA to align it wit the artificial star he became silent while focusing the Questar 7 image in my 4 mm Zeiss Abbe (700x) . His jaw dropped. After a while he started smiling and jumping up and down. Then he called out for his colleague Bart to come and see for himself what the noise was all about. He too started smiling after examining the image in the eyepiece. They both urged me to never ever sell this scope and to inform my wife and kids about the unusually fine optics and timeless value of this scope. I guess that is where Heirloom-value supercedes Strehl-value. By the way, the quality of the Questar 7 optics proved to be significantly better then that of my best APO's, which were also tested that day.

Clear and stable skies to all,

Erik

#2 Les

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Posted 01 October 2009 - 09:47 AM

Sweet! Did you pay extra to achieve a particular spec? Normally they are produced to deliver "diffraction limited" performance i.e. 1/4 wave. Were you commenting more on the smoothness of the surface?

#3 Erik Bakker

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Posted 01 October 2009 - 10:59 AM

Sweet! Did you pay extra to achieve a particular spec? Normally they are produced to deliver "diffraction limited" performance i.e. 1/4 wave. Were you commenting more on the smoothness of the surface?


Hi Les,

Years ago, I payed a premium price used because of the quality of this Q7. I have reported on this forum before about the stunning performance of the optics. I went to Opticon to have my refractors evaluated. The best of them was the little 55mm fluorite with very smooth optics and around 1/10th wave P-V.
Out of curiosity I couldn"t resist to put the Q7 on the test bench as well. It's diffraction image was visibly quite a bit better then even the 55 fluorite. Mind you, we were using my 4mm Zeiss Abbe. That's ca. 700x! In focus the image was perfect. So were the intra- and extra focal images. With incredible contrast between the light fresnell rings and the dark space inbetween. Smooth and precise optics as fine as the hands of man can make them. Just the reason why I bought it years ago after seeing it next to my 1/10th wave P-V Astro-Physics 130 refractor. The Q7 was quite a bit better then the AP EDF130. The great thing is, that the Q7 test INCLUDES the built-in diagonal, which therefore must also be of superb quality.
So thanks to the wonderful people at Questar, Cumberland and VernonScope for crafting this masterpiece back in 1985. :bow:

Clear skies,

Erik

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#4 SATMAN

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Posted 03 October 2009 - 02:03 PM

Erik,
This is why Questars are really amazing "the Finest Optics Created by the Hand of Man!"
I wonder how my Brandon 94 would have fared on this test visually it is just as good as the Questar.
In 1985 I don't think anything could have equaled the performance of your Q-7, or today for that matter.:bigshock: Some thing said about hand crafted and assembled optics! :bow::woohoo:
Hopefullly the weather will clear up here so I can get to observe soon we are back into our Rainy run again !@#$%
I purchased my Brandon Eyepieces back in 1986 and they still are my main planetary, general purpose eyepieces inspite of a good collection of Naglers that I have.
I am primarily a visual Observer now And these two telescopes (Questar 3.5, Brandon 94 APO)get the most use, I have just upgraded from a Vixen Porta-Mount to a Quarter Half hitch Mount on a KB1001 tripod for the Brandon.
Clear skys and keep enjoying that splendid optical system.

Gary

#5 Erik Bakker

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Posted 03 October 2009 - 03:32 PM

Clear skys and keep enjoying that splendid optical system.

Gary


Same to you Gary,

The Brandons are superb as is the 94 Brandon. And as always, Questars are a joy to use.

CS,

Erik

#6 dougspeterson

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Posted 03 October 2009 - 07:33 PM

Company 7 had a story about several Q7s tested with decent but not astounding numbers, 1/4 to 1/6 wave, and Peter Ceravolo showed an interferogram of a defective Q7 at an RTMC talk quite a while ago.

But mine from the late 80s has a simply superb star test so that I strongly feel mine exceeds those numbers and may be in the class of Erik's above. Were those Company 7 tests poorly done, or were there eras of superior quality?

#7 Erik Bakker

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Posted 04 October 2009 - 03:14 AM

Company 7 had a story about several Q7s tested with decent but not astounding numbers, 1/4 to 1/6 wave, and Peter Ceravolo showed an interferogram of a defective Q7 at an RTMC talk quite a while ago.

But mine from the late 80s has a simply superb star test so that I strongly feel mine exceeds those numbers and may be in the class of Erik's above. Were those Company 7 tests poorly done, or were there eras of superior quality?


Don't know. But congrats on your Q7 Doug. I do know that Opticon tested several Q 3 1/2 over the last decades, one being around 1/6 wave, the rest being significantly better. They consider Questar the initiator of consistently delivering very good optics to the end-user. They are very straight and critical testers AND amateur astronomers themselves. Of course, a Questar is somewhat handicapped by it's large central obstruction. A truly dedicated planetary system should have under 18 % CO in my opinion. But the Questar is a superb and extremely enjoyable compromise as far as I am concerned. Love touring the heavens with it.

Clear skies,

Erik

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#8 Les

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Posted 06 October 2009 - 12:33 PM

Company 7 had a story about several Q7s tested with decent but not astounding numbers, 1/4 to 1/6 wave,...


If I remember correctly from my last visit, C7 has the 1/6 wave unit on display in their "museum". Or maybe it was just the test report?? Anyway, the placard said that it was the finest Q7 that had ever been delivered to C7. I do remember someone on this forum commenting that they had contracted with Questar to produce a Q7 to the same spec as the Q50th i.e. 1/10 wave. I also remember Dr. Cohen saying that you could contract with Questar to build to a spec but that "time is money" and you can expect to pay thousands more. Still, it is a tribute to the Questar/Cumberland team that they have the talent and expertise to deliver these systems.

#9 Les

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Posted 07 October 2009 - 01:16 PM

Were those Company 7 tests poorly done, or were there eras of superior quality?


Let's remember that test reports that come with Questars are zygo measurements where thousands of points across the the mirror are examined. I believe that if a single point exceeds 1/6 wave then the slot in the report for P-V will show 1/6 wave. Now if there is a single point that high but the rest of the mirror is dead on that will produce a very different image than a mirror with a slow undulating 1/6 wave error across the whole mirror. So the distribution of the error is important. Strehl readings or rms reading provide additional information but ultimately it is the quality of the star image in a star test that can be most revealing. Obviously the opticians saw something in the testing of Erik's Q that they REALLY liked - and Erik is a lucky man to have such a fine scope.

#10 Erik Bakker

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Posted 07 October 2009 - 04:58 PM

Strehl readings or rms reading provide additional information but ultimately it is the quality of the star image in a star test that can be most revealing. Obviously the opticians saw something in the testing of Erik's Q that they REALLY liked - and Erik is a lucky man to have such a fine scope.


I am shure there are some other lucky guys/girls out there. Doug shurely must be one of them. Just felt good to share these results about the Q7 optics since they are so rarely reported. They really are very nice. I have never looked through another Q7 since they are very rare where I live.

Clear skies and many thanks to the great people crafting our Questars,

Erik

#11 Rick Woods

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Posted 22 October 2009 - 04:14 PM

Erik, Doug,

Exactly what were the numbers on your tests? Erik, yours was much better than your 1/10 wave APO: but what was it?
Come on, brag! We want to hear and envy!

#12 Erik Bakker

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Posted 24 October 2009 - 03:20 PM

Erik, Doug,

Exactly what were the numbers on your tests? Erik, yours was much better than your 1/10 wave APO: but what was it?
Come on, brag! We want to hear and envy!


Sorry Rick,

No bragging here. :lol:

Clear skies,

Erik

#13 pop

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Posted 05 May 2012 - 09:22 PM

I would like to see a test VS TEC6 or TEC MC200

Thanks

#14 vahe

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Posted 07 May 2012 - 11:58 AM

I would like to see a test VS TEC6 or TEC MC200


http://www.astro-for...utov-Cassegrain

Vahe

#15 coz

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Posted 13 August 2012 - 08:48 PM

Hi Eric, are your test figures on the Q7 still under wraps?

#16 Erik Bakker

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Posted 19 August 2012 - 11:53 AM

Yes, but the optics in my Q7 P-BB-5xx (now in other hands) are as fine as the hands of man can make them. They are limited by there 7" and 33% CO. And seeing and thermal equilibrium of course, like any scope.

#17 Bill Boublitz

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Posted 12 May 2013 - 10:44 AM

Big smiles reading this thread. They really have a mystique don't they?

I've had several opportunities to visit the Questar facility (it's about a three hour drive). One time, I'd been experiencing a problem with my fork mount. Jim Richert asked how the Astro Barrel was doing. "Superb," I answered and told him I regularly split binaries at or slightly below the instrument's Dawes limit. He shrugged and (without any ego), said,"Yeah, we regularly test them out at 0.4" on the bench." :)

As for the fork mount problem.... four years out of warranty and they fixed it, no charge. Threw in an eyepiece for my troubles. It doesn't get any better.






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