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| p.10 #9 · Nightscapes using AstroTrac Tracking Mount |
I'm new to these forums, and am very happy to have stumbled upon this discussion! I am an astrophotography guy as well, and from my little experience can say that Fred's results with the astrotrac are really excellent. Especially after just one month!
As you can see from all the great images in this thread (though some might have been captured with larger-aperture optics and guided equatorial mounts) good deep-sky images have one thing in common: lots of total exposure time.
Image stacks with low total noise can be stretched further to show subtle detail. You get low-noise stacks by using many exposures. There is a point of diminishing returns of course, but generally you should capture as many frames as you have the patience / clear skies for.
Another consideration is aiming for the longest possible exposure for each indiv frame ... the time limits should be limited by star trailing (due to tracking error/polar alignment), and by overexposure due to the skyfog limit (light pollution or moon sky glow). For DSLRs, a great rule of thumb is to check the histogram after a test frame -- try to have the main peak of the signal about 1/3 to 1/2 away from the left side of the histogram. This helps to separate the signal from the dark noise floor. Too far to the right and you risk overexposing stars (leading to white, bloated stars) and losing some dynamic range.
Apologies for the unsolicited advice, of course there are many approaches. Earlier in the thread there was some great advice to check out Jerry Lodriguss' guides.
Thanks for reading,