Re: [APML]: Image Registration

[Jerry Lodriguss <jml@astropix.com>]

The Astro-Photography Mailing List
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>I've had the same problem with Picture Window, and that was with virtually
>identical photos, taken back to back with the center and orientation exactly
>the same. (The autoguider continued uninterrupted during the two exposures,
>so these two photos were as exactly aligned as is humanly possible.)
>Nevertheless, a 4-point alignment near the corners still left very visible
>misalignments over most of the photo. I can't explain it, but I'm glad to
>hear I'm not the only one struggling with it. Any ideas?


Several things come to mind.

1. Someone said that Jonathan Sacks discovered a problem with the
registration engine in the current release version of PW.  I believe he
correted it in one of the later "astro" non-public releases, maybe the one
with the ADD function as an addition to the composite methods. Philip may
know the answer to this.

2. Film creep during the exposure.  I see this all the time on my negs shot
under same conditions you mention above.

3. Slight buckeling/warping of the film, different from frame to frame, in
the film holder during scanning.

4. Scanning irregularities, especially in scanners that move the film to
scan. Try scanning the same neg twice in a row without touching anything
and then see if you can perfectly align those two scans. Won't gain you
anything s/n wise, but might reveal if it's a scanning problem.

5. You're behind on your payments to the devil. <G>

Jerry
mailto:jml@astropix.com
Web page: http://www.astrosurf.com/astropix/index.html 
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