I can't seem to hit answers for search here on CN or wider on Google. Maybe I'm not asking the question properly..... Is there a tutorial/trouble-shooting manual on steps to take and what to look for?
I have tilt. Stars are better on one side and slowly get worse towards the other.
I recently bought an Askar Triplet ED 40mm aperture 220mm f.l. that comes with a triplet field flattener/reducer to f/4.5. Good news is that it is better than my Canon 70-200mm f/4 set to f/6.3. Frustrating news: the aberrations are not symmetrical one side to the other, implying tilt. The Canon 5Diii seems to give me symmetrical aberrations with Canon lenses, so I'm leaning to the conclusion the sensor is reasonably perpendicular and my issue is the Askar lens system. A local astro machinist measured my T-ring to be quite flat.
I put in a shim (first metal, then Astrodynium plastic) that improves the image! But, still not symmetrical. When the shim is between the T-ring and lens, it is best at one particular angle, but when the shim was between the FF and the objective, it was best 180 degrees the other side. Interestingly, the chromatic aberration is switched. This seems to imply in my inexperienced brain that if I shim both they might cancel out. [currently waiting 3 nights until next clearing to try].
But it's a lot of trial and error. I've looked but can't seem to figure out if CCD inspector will actually help me diagnose the source of the tilt, for a DSLR (Canon 5Diii). I'm not expecting perfection, but when one sees a result that is asymmetrical, it implies that something is out of line, and straightening is likely worthwhile.
Advice is appreciated!