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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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Jared
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Reged: 10/11/05

Loc: Piedmont, California, U.S.
Re: Trouble with flats new [Re: John Miele]
      #5654383 - 01/31/13 01:57 PM

Quote:

Does a flat have to be taken at the same temperature as the light frames? I don't think it does but wanted to check. Thanks...John




There is no requirement that it be taken at the same temperature. If, however, your flats are more than a few seconds dark current can start to matter, so in those situations I would want to dark subtract my flats. The flat-darks need to match the flats for temperature, but neither needs to match the lights. If your flats are less than a few seconds in duration, you probably don't need to cool your camera at all and can just bias subtract to get rid of the pedestal. The temperature of the bias frames won't matter either.

It's hard to give an exact answer on when you need to cool your flats (in terms of exposure duration), and when you need to dark subtract rather than just bias subtract. Depending on your camera's dark current and, in particular, on how hard you "push" when you are stretching your results will vary. Personally, I use Kodak based cameras that do not have particularly good dark current characteristics, and I can't tell a difference in my images with cooled vs. not cooled flats or dark subtracted vs. bias subtracted flats with 4s exposures. YMMV.


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Hilmi
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Reged: 03/07/10

Loc: Muscat, Sultanate of Oman
Re: Trouble with flats new [Re: Jared]
      #5655637 - 02/01/13 06:30 AM

Ok. Since I posted this message I have been busy repairing my mount. But last night I found the reasons my flats don't work. Its a reflection from the CLS filter. The brightness of the EL panel makes the reflection stronger and it spoils the flats

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shawnhar
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Reged: 06/25/10

Loc: Knoxville, TN
Re: Trouble with flats new [Re: Hilmi]
      #5656316 - 02/01/13 12:51 PM



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CounterWeight
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Reged: 10/05/08

Loc: Palo alto, CA.
Re: Trouble with flats new [Re: shawnhar]
      #5657773 - 02/02/13 09:32 AM

Congrat's on the detective work!

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