From: "jimchung2338" <jim_chung@sunshine.net>

Date: February 22, 2010 7:05:45 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: 60fps vs 30fps imaging

Last night I was doing some DSO imaging and I decided to pack it in early because transparency was falling.  Since the C8 was on the mount, I swung it to Mars and had a rare visual peek with a 4mm ep.  The seeing was quite stable and I could see a lot of surface detail.  Not wanting to waste an opportunity, I imaged Mars with my DMK21F04 colour ccd at both 60 & 30 fps.  At 60fps I had to turn the gains to about 90% so I expected a much noisier stack result than with the 30fps stack.  Both stacks exhibited very similarly shaped sharpness distribution histograms and the cutoff was chosen at 80% for both.

Both the 60 & 30fps stacked image were sharpened the same amount.

It appears that the level of noise reduction as a result of stacking many more images in the 60fps image enabled it to withstand a level of sharpening high enough to cause the 30fps image to breakdown and show artefacts.

http://tech.groups.yahoo.com/group/Astro_IIDC/files/Planetary/DMKMars.jpg

In the past I've always shot at lower frames rates thinking that I was ahead by having individual frames with lower noise.  This was a tradeoff I was willing to make even though a high frame rate would enable better freezing of the seeing.  It appears that stacking tolerates quite a bit of noise and a higher frame rate becomes the more desireable attribute.

Jim