I limit my exposures to 10-20s depending on where in the sky i image, it helps that i live 63 degrees north.
My setup is already sky fog limited after only 20 seconds despite using a DSLR, so taking short exposures is not really a problem. With the latest sensors it works even better with short subs. In fact what i find is that dynamic range is much better than when i used longer exposures on my dedicated rig.
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For long integration times the best strategy is to image an object for say 1 hour then catch it the same time next clear night and continue like that, this way you will not have to crop as much on the final stack as if you had imaged the same object for 6 hours on the same night.
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/Gabriel
Gabriel Wiklund