Dark Noise as a function of Bin Mode?

Using SharpCap for other Astro Imaging such as all sky cameras and meteor detection
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oopfan
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Dark Noise as a function of Bin Mode?

Post by oopfan »

Hi Robin,

A curious notion crossed my mind this morning: Does it make sense that Dark Noise should increase with Bin Mode?

Reasoning:

Dark Current is expressed as the number of electrons per pixel per second (e-/px/s).
Dark Noise is the square root of Dark Current.
If your camera has a Dark Current rating of 1e-/px/s then Dark Noise is 3e- after a 9s exposure. That is at Bin 1.
Now at Bin 2, each pixel is the sum of a four-pixel matrix, so Dark Current is 4e-/px/s and Dark Noise is 6e- after a 9s exposure. That is at Bin 2.

Does that make sense, or is it too early in the morning to be entertaining such thoughts?

Thanks,
Brian
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Re: Dark Noise as a function of Bin Mode?

Post by admin »

Hi Brian,

that all sounds correct, but remember that by applying the binning you've also collected four times as many signal electrons from your target, so there is no loss in S/N ratio.

Cheers, Robin
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Re: Dark Noise as a function of Bin Mode?

Post by oopfan »

Thanks, Robin, yes I agree that going from Bin 1 to Bin 2 yields:

4x the signal
1x the Read Noise
and now it appears: 2x the Dark Noise

Overall the SNR is higher but not as high as I originally thought.

Brian
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Re: Dark Noise as a function of Bin Mode?

Post by admin »

Hi,

don't forget that in areas with any signal – nebulousity or Galaxy or whatever – the shot noise of the signal comes into play. This is proportional to the square root of the signal, so if you multiply the signal by four then you double the shot noise.

Cheers, Robin
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Re: Dark Noise as a function of Bin Mode?

Post by oopfan »

Robin,

Got it! I should have said:

Going from Bin 1 to Bin 2 yields:
4x the Signal
2x the Shot Noise
1x the Read Noise
2x the Dark Noise

Still, overall you get a boost in SNR, but sadly you suffer the loss of image resolution.

Interestingly, I have seen people who mate a small pixel camera with a long focal length telescope, and then run the camera at bin 2, in normal operation! So for those of you who love your camera but want to upgrade to a longer focal length telescope, simply run your camera at bin 2.

Brian
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