Flat Overcorrects on New Laptop

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Dobsonion
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Joined: Fri Nov 23, 2018 4:57 pm

Flat Overcorrects on New Laptop

#1

Post by Dobsonion »

Kudos to Robin - SharpCap is powerful and valuable. Tonight I used the comet tracking for the first time and got good results (but failed on H2 because it was close to the moon). Anyway, my problem is with a new laptop. Am using same flat as on old laptop (which applied perfectly), same camera.
When I apply the flat, I get BRIGHTER corners than the middle (meaning overcorrection?). Brightness 10-12 on both machines.
Camera: ZWO 2600 color
Old Laptop: Win8 Sharpcap 4.0
New Laptop: WIn11 Sharpcap 4.1 (copied over that flat file)

Dobsonion
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Re: Flat Overcorrects on New Laptop

#2

Post by admin »

Hi,

are you using dark frames too? Really, flat frames for deep sky rely on having dark subtraction of the light frames and dark flat or bias subtraction of the flat. If you don't use dark frames then SharpCap does its best by using the bias level recorded in the flat frame (the bit with a percentage on the end of the name), but if you are using a different value for the brightness control (black level/offset on other camera brands) then that value will be wrong, leading to either under or over correction. So, that's my first guess - a different camera setting to on the previous computer, probably the brightness.

There are some general notes in the documentation on getting good flat frame correction that cover the points above in a bit more detail - see https://docs.sharpcap.co.uk/4.1/#Gettin ... Correction

cheers,

Robin
Dobsonion
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Joined: Fri Nov 23, 2018 4:57 pm

Re: Flat Overcorrects on New Laptop

#3

Post by Dobsonion »

Robin,
Thank you for your FAST response! {You are not charging enough for this software.]
I was also using dark subtraction. So the problem could be traced to a different Brightness setting.
I will investigate.
Dr. Brian
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Re: Flat Overcorrects on New Laptop

#4

Post by admin »

Hi,

yes, sounds like checking the settings for the light frames and dark frames match is a good starting point. These should match for everything that affects the image brightness (exposure, gain, offset/black level/brightness, colour balance adjustments). Good luck!

cheers,

Robin
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