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Old Dinosaur
Pooh-Bah
Reged: 05/08/07
Posts: 1255
Loc: Out in the sagebrush
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Just got my DMK21 and tried to give it some first light photons today, but clouds are covering me up.
I had just enough time to find focus and play a little with gain,gamma, exposure, and frame rates before I lost everything.
Anyone have some start up settings for the camera to get some images in Ha.
I was beginning to get a fairly good image of today's large prom before I lost the Sun.
Also, is the histogram useful for Ha? Seems like if I moved to what I heard ought to be around 250, everything was washed out and way over exposed.
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WRS Observatory
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pjr200
Carpal Tunnel
Reged: 08/29/07
Posts: 2406
Loc: Staffordshire, UK
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Hi John,
It will depend on if you are imaging surface or proms and the focal length you are using. As you increase the focal legth you will need to increae the expose times as less light will reach the ccd. For proms I try to keep the gamma as close to 100 as I can but then you will need to drop this when the trasparency is low otherwise the proms will be washed out (proms with a barlow-exposure is about 1/30secs). For surface shots I usually drop the gamma to about 20-30 to increase surface contrast (exposure is 1/60secs or less e.g. 1/120...). The histogram I only use for the surface with about 4/5ths of the levels full.
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Best regards
Paul Robertson
My Gallery
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Old Dinosaur
Pooh-Bah
Reged: 05/08/07
Posts: 1255
Loc: Out in the sagebrush
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Sounds like the rule of thumb I read about of keeping frame rate and exposure the same doesn't apply in Ha.
I only got a few minutes, but I noticed improvements if I ignored that rule above, don't know yet what that may apply to.
Quite a bit more camera than the old SPC900 I've been using.
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WRS Observatory
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brianb11213
Carpal Tunnel
Reged: 02/25/09
Posts: 2098
Loc: 55.215N 6.554W
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Quote:
Sounds like the rule of thumb I read about of keeping frame rate and exposure the same doesn't apply in Ha.
What rule of thumb?
The only one I know is to get the exposure short enough to deal with the seeing & shoot frames as fast as the camera & computer can go ... you need ~600 frames to get a decent s/n ratio with fainter prominences, and a really active one might be showing motion blur if the sequence takes too long to shoot, one minute is a realistic upper limit and less is better if you can get away with it.
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Old Dinosaur
Pooh-Bah
Reged: 05/08/07
Posts: 1255
Loc: Out in the sagebrush
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Before I splurged for a TIS camera I spent a lot of time checking them out.
I believe it was at the DMKCCD group I read about this "rule of thumb".
Ya gotta have somewhere to start, there ain't anything provided in the way of instruction manuals.
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WRS Observatory
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marktownley
Carpal Tunnel
Reged: 08/19/08
Posts: 2257
Loc: West Midlands, UK
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Quote:
Hi John,
It will depend on if you are imaging surface or proms and the focal length you are using. As you increase the focal legth you will need to increae the expose times as less light will reach the ccd. For proms I try to keep the gamma as close to 100 as I can but then you will need to drop this when the trasparency is low otherwise the proms will be washed out (proms with a barlow-exposure is about 1/30secs). For surface shots I usually drop the gamma to about 20-30 to increase surface contrast (exposure is 1/60secs or less e.g. 1/120...). The histogram I only use for the surface with about 4/5ths of the levels full.
Interesting reading this Paul, i'm going to save this thread in my faves and give it a go next time i'm out imaging. I've never touched the gamma tbh and have just left it on 100 all the time, will be interesting to see the difference. 
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Old Dinosaur
Pooh-Bah
Reged: 05/08/07
Posts: 1255
Loc: Out in the sagebrush
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For the image I just got I had exposure at 1/27th and played with gamma and gain till I got what looked like good exposure of the prom. I notice the brightness slider seemed to have no effect.
And also the tiniest slider movement in gamma and gain had huge effect and also exposure setting.
I used a 2X barlow to achieve focus.
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WRS Observatory
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DesertRat
professor emeritus
Reged: 06/18/06
Posts: 661
Loc: Valley of the Sun
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Quote:
Sounds like the rule of thumb I read about of keeping frame rate and exposure the same doesn't apply in Ha.
The rule of thumb referred to, and recommended by many imagers, is to try to keep the duty cycle of the camera close to 100% so that one is not increasing the gain at the expense of too much noise. Sometimes if the seeing is really dodgy you want to freeze seeing so that the rule has to be relaxed. And especially for a bright object like the Sun, even in Halpha, having exposure times much less than the reciprocal frame rate makes sense, given that daytime seeing tends to be really dodgy.
Glenn
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Brandon 94mm f7, Televue TV102 f8.6; GM8
Baader Wedge & Filters, Coronado SM90/BF30
IM715; C11 & C14; G-11 Gemini
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