It is still linear as far as I know. And the linearity is quite good, within a few percent. There is a community of astrophotographers interested in making phot

It is still linear as far as I know. And the linearity is quite good, within a few percent. There is a community of astrophotographers interested in making photometric measurements with DSLRs (American Association of Variable Star Observers). I think the harder part of the problem is getting a standard candle for calibration of your DSLR DN values to actual SI quantities. https://www.aavso.org/dslr-observing-manual https://www.aavso.org/dslr-observing-manual