purpose of master dark and how do I use it?

[John999R]

I should have asked this question before, but what to do with master darks that are generated by a photo session? I just simply included them in the stack and process them through DSS as any other dark frame. What is so special about them? I'm "new" at this because of a never-ending saga dealing with a defective mount that kept me from progressing in this hobby. Does the same solution apply to other master frames?

[UlteriorModem]

It would be used like any other dark.

Nothing really 'special' about them except they average out the signal.

The good thing is you dont have to do them every session. In fact I usually shoot them on a cloudy night. There usually good for 6 months or so or untill the weather changes. Then again I run a cooled camera so temperature is easy to control.

I tend to stick with 'standard' durations too so I make a set for 180, 240, 360 seconds at -15C. Good for a while.

[UlteriorModem]

Here is a snapshot of my calibration library.

[KathyNS]

If you process an image that includes 20 darks, the master dark generated by stacking them is the result of stacking those 20 darks. So, if you have another image in future with the same conditions (temperature, ISO/gain, exposure time), you can use that single master dark instead of the 20 original dark.

It is particularly useful for building a darks library, since you only have to save one file instead of the original 20.