Quote:
Originally Posted by ericwbenson
Lovely image, IMO you got the background just right, mostly smooth but with lots of faint specks from unresolved galaxies, really pleasing FOV.
I am curious though, do you know what the green ghost to the lower left of most of the bright whitish stars is from? One bad green frame?
Also what is the green+red pair of spots below NGC1365's nucleus and above the string of Ha nebula from, could they be related to above? Or RBI from a focus star?
I switched from FocusMax to PWI3 full frame focus a while ago to get away from focus star RBI, or I had to dither really big offsets.
Regards,
EB
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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