Quote:
Originally Posted by alpal
If your total exposure time was identical the lights would be perfect.
However the dark frames would be not matching perfectly as they
would be a little longer than a frame where no shutter was used.
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Not quite, the lights and darks could still match in length (e.g. 10 min total exposure) i.e. the dark signal accumulation would be 10 min for the dark and 10min for the light frame (dark signal accumulates regardless of shutter state), but the object signal accumulation is only for 5 min (50% duty cycle on shutter let's say), so the relative size of the dark signal relative to the object signal is twice as big, that's all. This is no problem for bright objects, where you have lots of signal to throw away, but for faint small stuff, not so much.
BTW this is the same strategy as lucky imaging with zero read noise cameras... throw away all the bad frames and stack only the good ones, but if your duty cycle is low because your seeing criteria is tight then it takes too long to record the faint details.
EB