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Exercise #4 CROA

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CROA
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Exercise #4 CROA

Open the roof of my observatory 1 hour before sunset and start the ST-7 camera to cool down. Now in the winter I keep the camera at – 18 C. (in the Summer to -10 C. )

I never change the position of the camera so I can keep my Flat's for a week before I replace them with a new Set, halve ways true my imaging run I take a few Dark's and when I finish for the night I take more Dark's and Bias. That keeps me going for the night and during the day I normally reduce my images. I never had any problems with the Flats but I notice that my Flats getting better with time, it is very challenging to do good Flat's, I usually do them at late afternoon and I cover the front of the telescope with a white t-shirt and a milky plastik screen, I do it for all my filters with variable exposures.

HQA
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T-shirt flats

Usually late-afternoon is still too bright, and flats have too short an exposure time.  If you wait until sunset, you still have quite a bit of time to take flats, though with changing brightness.  You might try flats at twilight and divide them by your afternoon flats to see if you get the same results within a percent or so - if not, experiment to find the best time for flats with your system.

Arne

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