Bad C11 optics? HELP!Posted By John Coffey |
THE PROBLEM:
I've got an old used black-tube C11 with "Starbright" coatings that appears to me to have REALLY bad optics.
Maybe I'm missing something, tho, so I'm asking for some EXPERT advice.
Please note that the questions I ask below are really only directed at you IF you actually KNOW the answers, or have some firm basis for offering your opinion.
I'm not too interested in wild guesses etc. What I'd really appreciate are reliable thoughtful answers from knowledgeable individuals who actually really know what they are talking about wrt non-obvious causes of poor optical performance, and/or who know a LOT about C11s.
(sorry if that sounded a bit rude. Didn't it mean to. I was just trying to be very clear about what I'm looking for here.)
THE SYMPTOMS:
The views this C11 produces are absolutely WORTHLESS. Simply atrocious. Not even in the ballpark.
Regardless of power, all the way down to 77x (24mm PAN w/0.66 reducer), EVERYTHING has a fuzzy/spikey colorless glowing edge. Stars, Jupiter, The Moon, everything. In-focus stars are little, round, fuzzy/spikey blobs. Uggh.
At higher powers this fuzzy/spikey edge grows until at a mere 280x (10mm Radian), Jupiter looks like a fuzzy white cotton ball. No detail at all. Just a fuzzy blob. Horrendous.
Also, there's LOTS OF COLOR in the INTRAfocal out-of-focus diffraction pattern (lots of orange with some blues & reds near the inner and outer rings). NO color at all on the EXTRAfocal side. This is the case regardless which eyepiece, reducer, or barlow is used.
INTRAfocal diffraction rings are a brightly colored fuzzy/spikey very LOW CONTRAST mess with 5-6 very fuzzy rings showing, but on the EXTRAfocal side, the rings are tight, contrasty & colorless.
There is no astigmatism apparent.
I'm not yet an expert at interpreting star test rings, so I can't tell you anything reliable about the degree of correction, zones, smoothness or other aberrations based on what I see in the eyepiece. All I can tell you is what I see described above.
CONDITIONS:
I'm using Radians & Panoptics with a Denkmeier power switch diagonal.
The OTA is perfectly collimated (per star test, concentric rings and all that).
All the optical components (primary, secondary & corrector) are all rotationally aligned with their alignment marks at "3 o'clock" as I understand they should be.
I even tweaked the primary alignment so that the primary focal point is dead on the optical axis of the primary baffle tube and is hitting the secondary dead center. Everything in this scope is aligned as perfectly as I can make it, and I'm quite capable of lining up optical components with high accuracy.
No tube currents were in evidence. The exterior of the OTA cylinder is insulated with silvered plastic bubble wrap insulation to reduce cooling issues (works great! Buy the bubble wrap at any Lowe's, it's in the insulation dept. Looks good on the OTA, too!)
The seeing was not perfect, but my Intes M703 was tack sharp under the same atmospheric conditions, using the same diagonal & eyepieces... and bubble wrap. ;]
QUESTIONS:
Is it possible for a REVERSED CORRECTOR to cause these problems? By "reversed" here, I mean "with the wrong side of the corrector is facing the stars." The scope was used when I bought it, so who knows what somebody might have done to it.
Is it really possible for a production C11 that passed Celestron QA 10-15 years ago or so to have optics that produce images this lousy? I find it hard to believe.
Shouldn't a typical C11 perform VERY noticably better than a high quality 7" Mak-Cass on Jupiter under the same 7-8 out of 10 seeing conditions?
What are the odds that a visit to Celestron could eliminate the "fuzzy" blur in the images and turn this scope into fine, sharp instrument (short of replacing all the optical components, that is)?
Do you have any other suggestions?
SUMMARY:
I don't know what to do. This is the only C11 I've ever looked thru. I can't believe they are all this bad. The only scope I can compare it to is my beloved Intes M703, and the C11 is optically not even in the same galaxy as the M703.
I'd love to turn this scope into a nice 11" light bucket, but the images need to be SHARP or what's the point?
I'm considering sending it to Celestron for a tune up, but after speaking to them, I did not have any confidence that they would be able to fix what's wrong with it.
On the phone, Celestron (even after getting someone from their optical shop involved) could not tell me with any certainty at all what could even be the most likely causes of all the "fuzz" or even the COLOR in the INTRAfocal diffraction rings. They just seemed really uncertain. I'm afraid that I'll spend $200 on shipping, then another $300 or so for a "tune up", and still have a really bad C11.
If you made it this far, thanks indeed for your attention!
Any help will be greatly appreciated.
Cheers!
John Coffey
I've got an old used black-tube C11 with "Starbright" coatings that appears to me to have REALLY bad optics.
Maybe I'm missing something, tho, so I'm asking for some EXPERT advice.
Please note that the questions I ask below are really only directed at you IF you actually KNOW the answers, or have some firm basis for offering your opinion.
I'm not too interested in wild guesses etc. What I'd really appreciate are reliable thoughtful answers from knowledgeable individuals who actually really know what they are talking about wrt non-obvious causes of poor optical performance, and/or who know a LOT about C11s.
(sorry if that sounded a bit rude. Didn't it mean to. I was just trying to be very clear about what I'm looking for here.)
THE SYMPTOMS:
The views this C11 produces are absolutely WORTHLESS. Simply atrocious. Not even in the ballpark.
Regardless of power, all the way down to 77x (24mm PAN w/0.66 reducer), EVERYTHING has a fuzzy/spikey colorless glowing edge. Stars, Jupiter, The Moon, everything. In-focus stars are little, round, fuzzy/spikey blobs. Uggh.
At higher powers this fuzzy/spikey edge grows until at a mere 280x (10mm Radian), Jupiter looks like a fuzzy white cotton ball. No detail at all. Just a fuzzy blob. Horrendous.
Also, there's LOTS OF COLOR in the INTRAfocal out-of-focus diffraction pattern (lots of orange with some blues & reds near the inner and outer rings). NO color at all on the EXTRAfocal side. This is the case regardless which eyepiece, reducer, or barlow is used.
INTRAfocal diffraction rings are a brightly colored fuzzy/spikey very LOW CONTRAST mess with 5-6 very fuzzy rings showing, but on the EXTRAfocal side, the rings are tight, contrasty & colorless.
There is no astigmatism apparent.
I'm not yet an expert at interpreting star test rings, so I can't tell you anything reliable about the degree of correction, zones, smoothness or other aberrations based on what I see in the eyepiece. All I can tell you is what I see described above.
CONDITIONS:
I'm using Radians & Panoptics with a Denkmeier power switch diagonal.
The OTA is perfectly collimated (per star test, concentric rings and all that).
All the optical components (primary, secondary & corrector) are all rotationally aligned with their alignment marks at "3 o'clock" as I understand they should be.
I even tweaked the primary alignment so that the primary focal point is dead on the optical axis of the primary baffle tube and is hitting the secondary dead center. Everything in this scope is aligned as perfectly as I can make it, and I'm quite capable of lining up optical components with high accuracy.
No tube currents were in evidence. The exterior of the OTA cylinder is insulated with silvered plastic bubble wrap insulation to reduce cooling issues (works great! Buy the bubble wrap at any Lowe's, it's in the insulation dept. Looks good on the OTA, too!)
The seeing was not perfect, but my Intes M703 was tack sharp under the same atmospheric conditions, using the same diagonal & eyepieces... and bubble wrap. ;]
QUESTIONS:
Is it possible for a REVERSED CORRECTOR to cause these problems? By "reversed" here, I mean "with the wrong side of the corrector is facing the stars." The scope was used when I bought it, so who knows what somebody might have done to it.
Is it really possible for a production C11 that passed Celestron QA 10-15 years ago or so to have optics that produce images this lousy? I find it hard to believe.
Shouldn't a typical C11 perform VERY noticably better than a high quality 7" Mak-Cass on Jupiter under the same 7-8 out of 10 seeing conditions?
What are the odds that a visit to Celestron could eliminate the "fuzzy" blur in the images and turn this scope into fine, sharp instrument (short of replacing all the optical components, that is)?
Do you have any other suggestions?
SUMMARY:
I don't know what to do. This is the only C11 I've ever looked thru. I can't believe they are all this bad. The only scope I can compare it to is my beloved Intes M703, and the C11 is optically not even in the same galaxy as the M703.
I'd love to turn this scope into a nice 11" light bucket, but the images need to be SHARP or what's the point?
I'm considering sending it to Celestron for a tune up, but after speaking to them, I did not have any confidence that they would be able to fix what's wrong with it.
On the phone, Celestron (even after getting someone from their optical shop involved) could not tell me with any certainty at all what could even be the most likely causes of all the "fuzz" or even the COLOR in the INTRAfocal diffraction rings. They just seemed really uncertain. I'm afraid that I'll spend $200 on shipping, then another $300 or so for a "tune up", and still have a really bad C11.
If you made it this far, thanks indeed for your attention!
Any help will be greatly appreciated.
Cheers!
John Coffey
