Analyzing Images

So, this is a post, but I might convert it to a page for reference at some point. I’m exploring how to analyze my imaging train for aberrations and what I can do about it.

ASTAP has a couple of built-in tools that make this easy. The question is what constitutes an aberration that is worth the effort of trying to correct. Here’s a recent image with M31 in the center. Note that top-left and bottom-right are in balance, bottom-left and top-right are slightly out-of-balance. The ASTAP summary is the tilt is little-to-none so it’s “opinion” is to leave it. Plus, this is actually a Rokinon 85mm f/1.4 image taken at f/4 using a (modified) Canon T6i, so I’m not sure how much I could do to adjust the tilt. Ideally, maybe something to support the lens instead of mounting via the camera mount.

The bigger “issue” is the off-axis aberration; a value of 1.02 doesn’t sound like much, but it is noticeable in the corners which puts a wrinkle in my plans to use this for a mosaic. I’ll have to see how much of the perimeter I need to discard when stitching images together.

The HFD contour maps tells the same story but does make it a lot easier to see the symmetries. The aberrations really are axially symmetric which is a good thing. If I were willing to work hard enough, I could probably figure out what the camera orientation was when this image was taken so I’d know which way was down. it would be interesting to know if that bottom-left to top-right difference in the previous map was on the up-down axis.