Quote:
Originally Posted by Placidus
Thanks, Eric. You've solved a long-standing mystery.
Definitely RBI, and not just from the focus star but from every star in the image. Had a look at the raw subs. It's not just in the green. We dither a lot between subs. There's always a perfect but shifted copy of the previous image. We absolutely don't want to go down the infrared pre-flash path. We've looked very closely both theoretically and experimentally at the effect of that on noise, and it's not acceptable (NASA recommends only using IR pre-flash at chip temperatures below about minus 70). Since we know the between-sub dithering exactly, and know the guy who wrote GoodLook 64 (our image-processing software), we could predict the amount of ghosting and either partially subtract or de-weight those pixels in that image, but for the moment I think I'll just file it under "irritating cosmetic issue to be addressed one day".
Thanks again for that.
Best,
Mike
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I agree with the pre-flash decision, my camera has it but I don't use it either. What cooler temperature are you using? I do 30min subs for almost everything at -25C and don't see such ghosting on field stars. It could be the 'CCD lottery' unfortunately. Processing them out would be a chore, remembering the order of the subs to now the previous exposure position, etc, certainly only a nice to have.
EB