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Is 7.25 seconds too long for CCD flats exposures?


bendiddley

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Used the CCD flats aid last night on APT with my CCD and flat panel. Coming out as 7.25 seconds. Set the ADU target to 30,000 and ADU range 10%. Not sure if these settings are right or what an ideal flat exposure time should be or whether it makes any difference being longer or shorter. I'm using some grey acetate on the flat panel as the lowest brightness without the acetate wasn't giving any results on the CCD flats aid. Any advice, tips welcome. Cheers.

Edited by bendiddley
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19 minutes ago, bendiddley said:

Used the CCD flats aid last night on APT with my CCD and flat panel. Coming out as 7.25 seconds. Set the ADU target to 30,000 and ADU range 10%. Not sure if these settings are right or what an ideal flat exposure time should be or whether it makes any difference being longer or shorter. I'm using some grey acetate on the flat panel as the lowest brightness without the acetate wasn't giving any results on the CCD flats aid. Any advice, tips welcome. Cheers.

Depends on the camera. My flats would be similar with my KAF-8300 camera, but you could try an in between brightness acetate.  Is the panel at max brightness now when using the grey sheet?

Edited by tooth_dr
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Thanks. Good to know yours would be similar, so obviously not unusual to be that length then. I'm using an SXVF-M25C. I read someone saying something about longer exposures introducing gradients into flats, just wondered if shorter exposures were better.

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  • 1 month later...
On 22/09/2020 at 11:42, bendiddley said:

I read someone saying something about longer exposures introducing gradients into flats, just wondered if shorter exposures were better.

Possibly, I've seen this when I tried flats in the day time, so now I always do them at night in the dark.

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Typing paper works fine as a dimmer and can be adjusted easily by adding or removing sheets.  With a CCD you don't need dedicated flat darks, you can calibrate your flats by using a master bias instead, though the flats exposure shouldn't be too long if you do that.

Olly

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