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You can reuse them, if you build libraries by temperature. There is a limit to the temperature range that an averaged dark frame is effective without producing too many artifacts.
Fresh darks are best and libraries are OK, particularly if you dither your light frames while imaging. A dithered stack will hide most of the temperature mismatch artifacts, among several other benefits - Backyard EOS.
Because you are averaging the noise by producing a master/super-dark - more frames is better. One image processing program suggest 10 as a minimum, but experience shows us that more is better. Taking longer darks than lights for the purpose of dark scaling (for which you must subtract the bias) is advanced stuff, if you need it.
There is a school of thought that says in-camera reduction is more effective per frame and just as effective despite half the exposure time - expect a big discussion/firestorm over that one.
If you have the time, segregate your darks by temperature. I don't think it's agood idea to mix them.
Hope this helps.
Last edited by rcheshire; 12-02-2014 at 01:02 PM.
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