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Old 20-05-2016, 10:33 PM
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Shiraz (Ray)
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Join Date: Apr 2010
Location: ardrossan south australia
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for interest, there has been a lot of consternation from people visually inspecting the darks from some of the cooled ZWO CMOS cameras and deciding that the relatively high levels of signal = high dark current. An explanation of the mechanism that introduces a pedestal (not dark current and no shot noise) in these cameras has been posted on the ZWO user group forum. http://zwoug.org/viewtopic.php?f=21&t=6204&start=30
" it turns out the effect you have finally identified looks like what is called clock feedthrough: when you retrieve your data from each pixel read transistor swithes and a parasitic charge is transferred from gate to drain which offset the ouput voltage, and it has no shot noise and is about the same over the chip. the way to make sure it is true is to measure the evolution of the shot noise with exposure time. You can infer the dark current from the shot noise as well to know the real dark current. Pierre"

Seems that the pedestal level has some dependence on the integration time, but it appears to be repeatable, so can calibrate out. Not sure how applicable this is to the 1600, but worth keeping in mind, since dark scaling may be a problem.

Last edited by Shiraz; 21-05-2016 at 06:22 AM.
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