Dark scaling different ISOs?

[troypiggo]

I broke my QSI583ws so am currently using my Canon EOS 5DII.  I read this post by Juan, and understand that the dark scaling is not dependant on matching image times or temperatures, which is great.  Doesn't specifically confirm that ISO does or doesn't need to match, though.

I've shot a dark library at ISO 1600, 15 min subs.  Can I safely use this dark library at ISO 800 for example, or do I need to do one at ISO 800 as well?

[Ignacio]

ISO setting is just a gain, so if you calibrate an iso800 sub with an iso1600 master dark (same duration and temperature), you should get a dark optimization factor of around 0.5. This will work only if you do an accurate bias calibration.

Granted that (nonlinear) hot pixels will not be fully calibrated. But if you did some dithering, those can be handled during stacking with outlier rejection.

Ignacio

[troypiggo]

Thanks mate.