Dark, Flat, Bias, Light frames... which really add to AP?

Started 3 months ago | Discussions thread
Astrophotographer 10 Forum Pro • Posts: 11,262
Re: Dark, Flat, Bias, Light frames... which really add to AP?

I don't know about other brands but with a Sony full frame the speckled colour noise in shadows is somewhat random so darks don't really correct it. They do remove a bit of amp glow that I have seen in the Sony A7r2.

Darks, flats, biases are more for deep sky long exposure work using a telescope, a mount etc.

Even then as mentioned some cameras don't really need darks.

I used a Starlight Express 694 which uses a Sony 694 CCD sensor. It was very clean and often didn't bother with darks.

I did find with that camera I would sometimes see fixed pattern noise that came through. A simple bias subtraction would get rid of that.

With DSLRs and mirrorless vignetting is simply handled in Lightroom or whatever with the lens correction tools.

Flats may well be vital in removing light pollution as they are really a type of gradient and are more in one colour channel than another. Often I found light pollution was in the green channel, but I suppose it would depend on the type of bulbs being used in the light pollution.

Short answer: stacking gets rid of most defects and vignetting tool gets rid of vignetting.

If you are using a tracker chances are the images are still being dithered (slight movement of the camera between exposures so the pixels don't line up) as the mounts are unlikely to be accurate enough to keep the image focused on the same pixel (with high MP cameras these days) exposure after exposure.

Greg.

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