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Old 13-10-2019, 10:08 AM
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gregbradley
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Join Date: Feb 2006
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I don't know if this applies to the QHY600 but the Sony A7riv (same sensor)
has a dual gain analogue to digital converter as do the earlier A7rii and iii cameras.

At ISO320 the read noise drops from this dual gain converter.

So if that is the same for the QHY600 (ADC is on the sensor back face so it probably is the same) then you may need a set of flats for before ISO320 and after ISO320. The bias would be different.

I don't think the QHY600 uses ISO but I wonder how that works with the ADC probably programmed by Sony to include that dual gain?

Perhaps this is not relevant but worth mentioning in case it is. I suppose you would need to know what gain setting that ISO320 threshold is.

As far as flats go I think they are part science and part Art! I tend to play with my calibration files to make sure they are working before I finish an imaging run. I don't bias subtract my flats when making a master flat. I list it separately when doing the dark subtract etc. I also tend to use adaptive darks and use the bias for them as well.

Overcorrecting flats in my experience is from overexposed flats. It can also be traced to a mismatch of bias (not fresh enough) or slightly off darks.

What can complicate things are the different readout rates and resultant different read noise available with some cameras (notably FLI, they offer a fast readout for focusing but higher read noise and a slower download but lower noise). If you mix them up flats won't work well.

These days with most scopes having lensed correctors/flatteners etc there are often bright centre spots and increased vignetting which can be a challenge to correct.

Greg.
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