QHYCCD QHY168C User Manual page 22

QHY168C
gain is set to a low value, the number of electrons that 1 adu corresponds to is more than 1, which
will cause quantization error and negatively affect its performance in low-light environment. So
when you take a long time exposure frame with a CMOS camera, it's recommended to set the gain
to the Unity Gain. For QHY168C, its Unity gain = 10.
When you use Lucky Imaging technique, because the exposure time is very short, the number of
captured photons is very limited and the sensor can hardly get saturated. It's recommended to set
the gain to a high value. The readout noise of CMOS camera will drop when you increase the gain.
Setting the gain to a high value can reduce the readout noise so that the limited photon will not be
drawn in the readout noise.
If you want to know more about gain and offset setting, here's a great article talking about it:
http://www.stark-labs.com/help/blog/files/GainAndOffset.php
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