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### Optimum ratio of dark frames to light frames?

Posted: Thu Aug 03, 2017 11:31 pm
Robin,

When I launch the dialog to begin dark frame acquisition it defaults to 10 frames. I have always wondered if there is a magic ratio of darks to lights that achieve the best result. My gut tells me that if I aim to only collect 100 lights then 10 darks are acceptable, but if my goal is to collect 1000 lights then I might want to increase the number darks. Am I onto something or is my gut wrong?

Thanks,
Brian

### Re: Optimum ratio of dark frames to light frames?

Posted: Fri Aug 04, 2017 8:55 am
Hi Brian,

it all comes down to a moderately complicated noise calculation. Noise in an averaged frame is SQRT(n) times smaller than the noise in an individual frame, so if you take 16 frames to make your master dark the noise is 4 times smaller, if you take 100 it is 10 times smaller.

Ideally you want the noise from the master dark to be smaller than the noise in the stacked light frames.

For an individual frame

Dark Noise = Read Noise + Thermal Noise

Light Noise = Read Noise + Thermal Noise + Shot Noise

If you have a dig around on the web you will find people have considered this in great detail already and you'll find calculations you can apply to your situation.

cheers,

Robin

### Re: Optimum ratio of dark frames to light frames?

Posted: Fri Aug 04, 2017 12:59 pm
Hi Robin,