Dark frame subtraction

[Graham_of_Rainham]

Has anyone done any tests to determine if it's better to do Dark Frame Subtraction using the camera or using post processing software

If you take a 10 minute exposure and the camera then does another 10 min exposure with the shutter closed, performs the subtraction then stores the image, will the sensor be hotter having been active for 20 mins and have more "anomalies"

If you make a 10 minute exposure, with the lens cap on, eye piece covered, in a dark room, can this be used as a "Dark Frame" for use in Photoshop (or whatever)

How much difference is there between Dark Frames of different exposure duration.

Thanks

[Ian]

I think the problem with this is that the dark frame has to be produced under the same conditions as the actual exposed frame. That way, the noise to be canceled out will be the same in both frames.

Any way, the heat in the sensor will reach equilibrium and remain constant after a certain time, probably well before the end of the exposure time.

Ian

[Graham_of_Rainham]

Originally Posted by Ian

"I think that the dark frame has to be produced under the same conditions as the actual exposed frame. That way, the noise to be canceled out will be the same in both frames."

Ian

I think you are right. Interestingly there are some that are advocating that an average of a set of "Dark Exposures" can be used to better effect in PS.

One advantage of the PS technique is that the camera is not "idle" for the additional duration of the dark frame exposure.

I guess I'll just have to try out the two and see what works best for me

[magicaxeman]

The camera reaching equilibrium does somewhat depend on the conditions on the night though, on a cold night doing the dark frames after the camera has cooled again would yield better results, at least it does as far as astrophotography goes.

We used to do dark frames on site, but flat frames could be done at home using a modified light box.