That is, 1.5C difference in dark noise where the temperature of the light frames falls midway between two dark libraries. Or 2.5 if the spacing is 5C.
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That will make for one big darks library. What number of exposure groupings would you suggest? 5 to 50 in steps of 5?
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Convention is to take sufficient darks at a temperature, iso and exposure length to provide a reasonable average of dark noise.
If you know before hand what the iso and exposure times will be for the majority of your work the variable is temperature, and unless your camera has regulated cooling, you will find that the libraries will be acquired at other than nicely ordered 3 or 5C increments. You can limit your requirements within typical exposure and iso values rather than creating a vast number of predetermined libraries that you may never use.
As dark noise is a function of iso and temperature, a short exposure time at high temperature, may come close to a long exposure at a lower temperature. This can get messy.
Personally, I take darks at each session, except when using my cooled DSLR. These can be stored for future use.
