Question about an Uncooled Camera and Dark Frames - RAW Shooting and Processing - CHDK Forum
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Question about an Uncooled Camera and Dark Frames

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Offline yardleydobon

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Question about an Uncooled Camera and Dark Frames
« on: 02 / July / 2010, 03:37:47 »
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I'm working on a project that requires I shoot many long exposures (around 3 seconds). My camera is uncooled so it heats up as I take the pictures. I have two ideas on how I should handle dark frame subtraction. I'd like to hear from those more experienced than me which is the better choice.

1) Warm up the camera (take throw away pictures?) until the camera reaches a constant temperature. Then take darks and then lights. I've never tried this. Does it work?

2) Just let the camera do the dark frame subtraction after every shot.

Problems I can see with (1) is that it might take a long time and increase wear on the camera if I have to take throw away pictures.

The problem I see with (2) is that a single dark frame subtraction will remove the dark current but will also add more noise than a master dark made from many darks would and that the noise will grow as the camera heats up. I know that I can average several light frames to get rid of noise, but is this technique still appropriate if the noise grows from one shot to the next? I believe the noise's probability distribution stays the same.

It's been a long while since I've done anything with random processes but I think expressing the averaging of shots with growing thermal noise with the following expression makes what I'm trying to say clearer.

[(L+N)+(L+k1*N)+(L+k2*N)+(L+k3*N)]/4

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Offline PS

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Re: Question about an Uncooled Camera and Dark Frames
« Reply #1 on: 04 / July / 2010, 15:38:46 »
If it's about noise reduction then Tv bracketing is ideal for this task.
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Offline yardleydobon

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Re: Question about an Uncooled Camera and Dark Frames
« Reply #2 on: 23 / July / 2010, 21:13:04 »
Because I'm doing photometrics I don't believe Tv bracketing is acceptable. I reposted my question at the cloudynights.com forum. I received a more fruitful response there. I hope that doesn't sound like I'm knocking this forum. Here's a link to the cloudnights thread if anyone is interested.

Cloudy Nights
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