10725Re: [tmboptical] Re: Final squareness/lens test. Problem found
- Aug 8 2:37 PMI have forgotten the details of your tests, but one possibility is that
the focuser is sagging a little. I have this on the TMB 80 and tested
with an ST10. The focal plane is quite a way back from the focuser.
Hopefully Markus can make an OTA extension to get round this problem.
In message <bh0omu+q8jl@...>, digidodi <ddierick@...>
>Well, it's not the camera either. I made pictures last night with an--
>MK69 Intes, full frame with the D100, and in all directions the image
>is tacksharp. I used the same camera and adapter. The only thing
>which is not the same is the Televue reducer. I have now also a Borg
>flattener to rule out the Televue.
>It puzzles me as much as it puzzles you. I will do the test with the
>new tube as soon as possible!
>--- In email@example.com, "Markus Ludes"
>> the tube arrived here. A laser test showed that the mechanical
>parts have been straight. A coolimation test of the lens showed both
>reflections to be 100% concentric too, the startest used up to any
>power was also perfect.
>> As dominique wished I have send him back his tube with another
>which passed the test in same way.
>> To be honest I have no idea whats going on here, but in my opinion
>it cannot be the tube and it cannot be the lens, otherwise one of
>both must show a fault.
>> will be interested to see the new images from Dodi
>> ----- Original Message -----
>> From: Richard Chalfan
>> To: firstname.lastname@example.org
>> Sent: Friday, August 01, 2003 9:30 PM
>> Subject: Re: [tmboptical] Re: Final squareness/lens test. Problem
>> --- digidodi <ddierick@h...> wrote:
>> > Unless as I suspect the error is lateral in the lens
>> > or cell. Then
>> > you would still have good on axis performance, but
>> > as all
>> > photographers know, if you move the camera laterally
>> > away from the
>> > axis for one reason or another, you get uneven
>> > aberation because you
>> > are putting part of the image zone outside the
>> > aberation free image
>> > circle. I think this is what's happening.
>> If by lateral error, you mean that the optical axis of
>> the lens does not go down the center of the tube (that
>> is, the optical axis is offset from the tube's
>> mechanical axis, but they are parallel), then yes,
>> your CCD images would look like what you posted.
>> Your pictures model my earlier suggestion too. The
>> aberrations on one side are more pronounced than those
>> on the other side if the CCD is perpendicular to, but
>> not centered on, the mechanical (and optical) axis of
>> the scope.
>> But if the lens is perfect and the optical axis of the
>> lens is perpendicular to the CCD chip, though
>> laterally offset, you should be able to see that in a
>> star test.
>> The Airy disk rings will only be perfectly concentric
>> ON the objective's optical axis. With a laterally
>> offset axis, you would see perfectly concentric rings
>> off of the center of the field, and non-concentric
>> rings when the star was in the middle of the field.
>> The reason I earlier suggested an offset chip, is
>> because that condition still gives a perfect star test
>> in a perfect scope. It is the only condition I can
>> think of off hand, where you get a perfect star test,
>> but your CCD image is both properly focused and
>> abberationally unsymmetrical.
>> If the lens is tilted (the objective axis is at an
>> angle to the tube's mechanical axis and to the
>> eyepiece axis) then you will see an Airy disk with
>> off-axis aberrations. And your CCD chip should have a
>> band of good focus, going slightly out of focus on
>> either side of the band.
>> If the lens elements are not mounted properly within
>> the cell, then you will not see a "perfect" Airy disk
>> even on axis. I think it would look rather
>> So your symptoms sound slightly conflicting. However,
>> if the errors are small the "theoretical" symptoms may
>> be hard to detect. I think sending the tube back to
>> Marcus is a reasonable start. It is possible though,
>> that he will find no problem with the lens or the
>> Please let us know how this turns out.
>> Good luck!!!!
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