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Old 09-11-2018, 03:43 PM
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Atmos (Colin)
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Join Date: Aug 2011
Location: Melbourne
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Typically CCDs only have dark current that is different from the bias. If you’re using a sensor that has very little dark current and you’re cooling it to maybe -20°C and below then the difference between a bias frame and maybe a 5s dark frame is not going to really be noticed. I started off with a QHY9 which also used the KAF-8300 sensor and needed at least 3-5s flat exposures to remove the shutter from the flat. In this instance I was better off with a 4s flat dark as it better represented what I wanted to remove than a bias.

Many CMOS sensors have amp glow which is another form of dark current but it is non linear, meaning, it doesn’t increase linearly as dark current does. Used both an ASI1600 and QHY163M and I’ve found (and at least QHY have suggested) that using exposures shorter than 0.3-0.5s will cause issues when it comes to calibration so the use of bias frames hasn’t been recommended.
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