Wednesday, February 22, 2012

Good seeing, bad calibration

Details of my (flawed) flat fielding in MaxIm (click for full size version)
Seeing last time out, Feb. 19th, was the best I have experienced so far while working a long focal lengths. Typical stellar FWHM on long exposures was 2.2 arcsec - on most nights I get ~3 arcsec. That was great! Not so great was the calibration problems I encountered in MaxIm DL Pro. I use a SBIG ST10-XE camera and in the past I have used Mira for calibration. I take a bunch of flat fields using the twilight sky and a white cloth in front of the scope. All light and flat frames are followed up with dark exposures of equal length, so there is no need for bias frames. The sky flats vary quite a lot in their brightness due to the increasing sky brightness, but this is normally of no concern since the frames are scaled after dark subtraction to match each other before the images are combined. However, when using the calibration features of MaxIm the flat fielding failed to remove dust doughnuts. When I processed the same frames in Mira the flat fielding went just fine - hence I suspect some problem in MaxIm, either due to my ignorance or due to a bug. I really want to switch to MaxIm since it has many good features that work well. The image below details what I am doing. A few of the original raw files can be downloaded here (28MB) - can someone with MaxIm do a good calibration with this and send me some advice? My email address is - thanks!


  1. Hi Mikael :-))

    Sorry I made the foregoing post in Danish. I didn't notice.

    I also wonder why I didn't a notice from concerning you new posts, as I initially after your first mail subscribed as i "Follower". But I am not good at these technical issues :-/

    I can't advise you regarding flat field calibration in Maxim. I use PixInsight, which functions fine. I only use Maxim for guiding.

    - Henrik

    1. I don't know much about replying and following either! Otherwise, just use mail. So far I have not received any help on the calibration problem - eventually I will contact Cyanogen directly, since it is a 'must solve'...