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Old 06-03-2013, 07:47 PM
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PRejto (Peter)
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Flat Frames for Ha?

I am trying some Ha imaging for the first time, but I seem to be stuck understanding how to get flat frames. I tried in the normal way but even very long exposures will not register anything through the Ha filter. What do you guys do?

Thanks!

Peter
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Old 06-03-2013, 08:31 PM
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RickS (Rick)
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Peter,

Flat frames with narrowband filters require longer exposures and/or turning up the brightness of your light source. There's no other magic to it. You should be registering some signal from a long exposure unless your light source is very dim.

How long have you tried? What are you using for the light source?

I normally use a LED light box. I run it dimmed for LRGB and at full power for narrowband. My narrowband exposures are usually 10-20 seconds.

Cheers,
Rick.
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Old 06-03-2013, 08:42 PM
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batema (Mark)
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I do flats using my light box for luminance for 10 seconds on the dimmest light whereas for my Ha I turn up the light box to max brightness and take 10 second flats.
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Old 06-03-2013, 09:38 PM
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Well, something is going wrong! I have a light box made by Peter in Adelaide. I turned it full bright and even tried 10 min....got nothing but black. I tried a few times but I certainly will try again. My Ha filter is an Astronomik 12 nm.....

Thanks for the answers!

Peter

EDit: Ok, got this figured out. My exposures were way too long, but for some odd reason my imaging program displayed those images as totally black. So I tried CCDSoft and the same exposure gave totally white. Finally I tried some impossibly short exposure of 1 sec and suddenly I am seeing a flat (this with the box full on). The totally black image even after 10 min had me fooled. Still not sure what that is about.

Last edited by PRejto; 06-03-2013 at 10:37 PM.
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Old 07-03-2013, 09:26 AM
WingnutR32 (Sam)
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Were you using MaximDL for the images Peter?

If so, the automatic screen stretch will make a completely over exposed image, black..
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Old 07-03-2013, 11:10 AM
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multiweb (Marc)
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I usually don't have to go in excess of 3-4s for Ha flats. Check your histogram. Should be 1/3 up towards the right.
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Old 07-03-2013, 08:48 PM
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Rigel003 (Graeme)
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Quote:
Originally Posted by WingnutR32 View Post
Were you using MaximDL for the images Peter?

If so, the automatic screen stretch will make a completely over exposed image, black..
I've had that experience with Maxim. Took ages to work out what was going on. You'd expect complete white for a gross overexposure.
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