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Dark Frame Scaling For Uncooled DSLR


(@aditya_photos)
Brown Dwarf Customer
Joined: 1 year ago
Posts: 11
Topic starter  

Hi there,

I hope you are doing great.

I wanna have some questions regarding Dark Frame Scaling.

I am a DSLR user and do Astro and Deepsky Astro for enjoyment. I know the limitations of uncooled DSLRs.

I understand all the basic concepts needed for this hobby. As summer here, DSLR sensors produce a lot of thermal noise and hot pixels. During winters, sometimes I never take dark frames but dither manually (i have a star tracker, but I can do it on both axis) as the temperature was 5-15 degrees below zero. I try to dither after every few frames no matter the season I shoot.

But now its summer/rainy humid season and now the temperature is approx 28C to  35C.

So, the point is, if I make a master dark for 50-100 frames with 5 min subs at ambient or room temperature (between 25-30C/ different night/day, can I use them for the whole summer season?

If yes, then what ISO should I pick? Does it matter for dark frame scaling? Or will it work if I make a master dark from my all darks that I have taken so far at different temperatures, seasons, sub-length, and ISO? what would be a good strategy?

Please share your experiences.

TIA


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(@jochen-scharmann)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 74
 

Hi Aditya,

yes you can use darfkrame libraries. As a rule of thumb, noise level doubles each time when temp raises by 7C on DSLRs. However, this relates to the sensor temp (which is more constant once the Cam is working a few min), not the environmental temp. The usual advise is to have masterdarks for each 2-3C steps, in Your case You could get waway with 28C, 31C and 35C and pick the closest. I think the scaling only works well with ISO & exposure time changes, which behave more linear, not with temp which is very non-linear and strongly depending on the Cam. Note: You need to renew the libraries once or twice every year. 

Clear skies,

Jochen


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(@wvreeven)
Galaxy Customer
Joined: 4 years ago
Posts: 2090
 

@aditya_photos Adding to Jochen's excellent answer: dark frames need to have the same ISO as the lights and preferably also the same exposure time. If the exposure time is different then you'll need bias frames of the same ISO as well.

Wouter


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