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Old 31-01-2019, 07:22 AM
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bojan is offline
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,166
Originally Posted by Jasp05 View Post
Would it be worth trying to make an artificial star for testing fwhm once adjustments have been made?

Or can i just rely on focus from examining the image after a test shot is done. At least the star test would give me a way to measure if focus is better?

Probably worth it... this is (I believe) how manufacturer adjust those things (not artificial star, but definitely test pattern is used).

(For example, I have a problem with one of my lenses (Samyang 500mm F/6.3), it suffers from coma in frame corners, while centre is OK (and it is only my specimen that shows this problem, others are OK ).

I plan to use red laser module and another catadiopric lens (MTO 1100) as colimator, so my artificial star will be at optical infinity. Then I will try to adjust coma by moving the back lens group and checking the image quality using live view.)

Test shot is easiest way to determine if focus is OK or not.
Maybe you should use autofocus at distant object while it is still light, then switch to MF and wait for a dark to take star test?

At some point when modifying my 450D I was thinking about checking the distance (and tilt) of the sensor with some sort of microscope at high magnification, this arrangement should have a very narrow focus depth, but there was no need for that, tilt was acceptable, and I am using that camera exclusively for AP.

Another way to test tilt would be to try to use laser beam reflected from sensor glass cover (assuming it is parralel with sensor plane).

Something lik ethis one:

I have laser distance module that uses self-interference with reflected beam, thus detecting the change in distance.. it is VERY sensitive, resolution is well below 1um).. To use it for that purpose, first I need to locate it (somewhere in my cubboards), then I need to make flange adapter.... this is a project for future.

Last edited by bojan; 31-01-2019 at 07:42 AM.
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