Quote:
Originally Posted by TrevorW
This was done as an experiment, I can't use my guidescope at the moment so I wanted to see how much I could capture with only 40 second exposures and bring out in processing for future reference
total 17 minutes 26 frames ISO800

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I found this really interesting as it highlights many areas of digital image capture and processing that are often not well understood.
For example, shot noise is not removed by bias frames. (shot noise is statistical in nature and related to the flux of the object)
It also highlights a very important aspect of stacking images: you need to capture signal faster than you capture noise for the process to be worthwhile.
For dim objects, the signal level of the object approaches the noise floor
and stacking will only increase the signal marginally faster than the noise...hence the result you posted.
Some better known fixes are:
improve the S/N ratio by moving to a dark site, high contrast optics, and perfect focus
use a larger aperture,
a higher QE sensor,
lower the sensor noise (ie cool it)
BTW I covered much of this in my talk at the CWAS Astrofest in 2008