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Old 16-02-2016, 08:51 PM
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Somnium (Aidan)
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Gain and flat frames

just wanted to check and see if it is critical to capture flat field and light subs at the same gain settings, i am having a few issues with my data reduction and was wondering if this was the issue.
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Old 16-02-2016, 10:48 PM
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Atmos (Colin)
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With the QHY9, if you change the gain it may change the bias although I would have to double check that.
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Old 17-02-2016, 08:18 AM
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Thanks Colin, i will check that out. i took some flats with the original gain settings and it seemed to have worked. although i had 5 ours of the antennae galaxies at too high a gain so as to make obtaining flats impossible. the thing that is really frustrating me now is when i stretch the images i have a gradient from top left to bottom right and i cant figure out what is causing it.

i thought it was an artefact of the shutter on the QHY9 when taking 1 second subs but i managed to take 6 second flats and still had the issue.

there may be some sort of internal reflection, either in the telescope or from the observatory. i will try imaging a different part of the sky tonight and see if that solves the issue ...
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Old 17-02-2016, 12:16 PM
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I suppose if you were to take some bias at that higher gain you would be able to correctly calibrate the high gain flats for the corresponding subs.
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Old 17-02-2016, 12:37 PM
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Quote:
Originally Posted by Somnium View Post
just wanted to check and see if it is critical to capture flat field and light subs at the same gain settings, i am having a few issues with my data reduction and was wondering if this was the issue.
Absolutely. Shoot your calibration frames at the same temperature and same gain/offset as when you shot your light frames.
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Old 17-02-2016, 12:54 PM
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Absolutely. Shoot your calibration frames at the same temperature and same gain/offset as when you shot your light frames.
Thanks, I feel like I am learning everything about this hobby by making every mistake possible
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Old 17-02-2016, 01:04 PM
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Thanks, I feel like I am learning everything about this hobby by making every mistake possible
I lost a whole night at Coonabarabran a couple of years ago because I inadvertently changed the gain of my camera. Lesson learned. There's always one more mistake to discover out there that you haven't done yet. That's the fun part of the hobby. ... or you do the same again, that comes with age.
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Old 17-02-2016, 01:34 PM
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Fair enough , I bet this light gradient issue is going to turn out to be something really stupid too but right now it is showing up in all my images
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