Converting the camera to prime focus - page 3 - General Chat - CHDK Forum
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Converting the camera to prime focus

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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #20 on: 22 / May / 2008, 02:52:48 »
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I would guess that's a lens flare.. Does it apepar in the pictures as well?
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Offline dzsemx

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Re: Converting the camera to prime focus
« Reply #21 on: 22 / May / 2008, 04:51:39 »
it's not lense flare... on images does not appear at all, only in preview and video... i saw this on many digtal cameras... camcorders generally does not have this problem
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #22 on: 22 / May / 2008, 14:10:04 »
Then I guess it has to do with not using the shutter. Maybe the CCD gets overloaded because the exposure time it too big?
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Offline DataGhost

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Re: Converting the camera to prime focus
« Reply #23 on: 22 / May / 2008, 14:54:42 »
It's called a CCD artifact and indeed, my N80 doesn't experience it so it probably doesn't have a CCD :)
Quote
Each pixel can store only a certain amount of electrons (of the order of 100,000). If a pixel is illuminated by a bright star and/or if the exposure time is long enough, that pixel will fill up, and the electrons will start to fill the neighboring pixels: the CCD is saturated. When the image is read, all the extra electrons will be spread over the column containing the saturated pixels, making a saturation trail, as shown in Fig.11.
Source
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Offline dzsemx

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Re: Converting the camera to prime focus
« Reply #24 on: 23 / May / 2008, 01:46:55 »
yeah it's something like those...
s5is has these vertical lines?
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Offline LjL

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Re: Converting the camera to prime focus
« Reply #25 on: 08 / July / 2008, 18:22:29 »
When someone said "webcams don't count"... right, but don't discount them when investigating possibilities for prime focus! Just Google "webcam astrophotography", if you haven't already, and you'll find out that certain webcams are fine and relatively cheap candidates for prime focus astrophotography!

Mine can be connected to my telescope by just using a film canister, since the lens hole is the exact size of one... but then again, my webcam is absolutely [admin: avoid swearing please], so can't really be used for this at all ;)

EDIT: Meh, saying that something is absolutely [admin: avoid swearing please] is not swearing. I'm sure I could come up with real swearing that your filters wouldn't catch  :haha
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #26 on: 09 / July / 2008, 00:53:22 »
Webcams are OK for some stuff, such as the solar system. But they are useless for deep sky stuff (unless if you have some huge aperture).
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Offline LjL

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Re: Converting the camera to prime focus
« Reply #27 on: 09 / July / 2008, 07:10:31 »
Is that because of the low sensitivity, or merely because the sensor area (since it's prime focus we're talking about) is too small to capture an entire nebula?

I thought especially some of the older (black and white, Logitech Something above al) CCD webcams were pretty sensitive to low light...

But yeah, I've mostly seen them used for the solar system indeed, and I must say the results impressed me.
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #28 on: 09 / July / 2008, 11:33:57 »
It's mainly because even hacked web cams can't have long enough exposures for deep space stuff. For example, it is not uncommon for astro photographers to have 3 1 hour exposures (each with a different color filter).

So with a Canon webcam you can get 65 seconds exposures and stack them together, and possibly get some acceptable quality pictures. But with a webcam, I don't think you can go that high with the exposure.
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Offline LjL

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Re: Converting the camera to prime focus
« Reply #29 on: 09 / July / 2008, 11:45:12 »
Isn't stacking, on a CCD, better than doing long exposures? I thought noise would average down much better, and you could also get better resolution by avoiding drift (with a good aligner).
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