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Converting the camera to prime focus

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Offline dzsemx

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Re: Converting the camera to prime focus
« Reply #10 on: 21 / May / 2008, 02:45:48 »
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Quote from: RaduP on 19 / May / 2008, 05:12:05
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The Canon powershots do not use the shutter in movie mode (I assume).
I don't think any consumer camera uses that.
They just skip the lines, so only the lines with proper exposure are used. This sucks, because it would have been much nicer if the video mode actually took the whole sensor data then resized it to 640x480 (so much better noise reduction and image definition).

I have a DSLR camera that I do use with my spotting scope, but the advantage of a P&S is that the pixels are much smaller so in the crop factor is bigger. Of course, you get more noise, but sometimes the tradeoff is acceptable.

my a650is gives about the same result(same noise) in video mode like resizing the 12megapix data to 640*480(took with 1/30)...
many sensors can do live preview with some downsample in hardware...
only the cheapest cameras (and cameraphones) uses the "skip line" live view mode(i saw at many ultracompact cameras)
« Last Edit: 21 / May / 2008, 02:52:52 by dzsemx »
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #11 on: 21 / May / 2008, 02:51:25 »
Well, if they do that, it means they have some electronic shutter on their CCD, or else they would have to flip their shutter 24 times a second in order to avoid the different exposure on different lines of the sensor.
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Offline dzsemx

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Re: Converting the camera to prime focus
« Reply #12 on: 21 / May / 2008, 03:12:56 »
Quote from: RaduP on 21 / May / 2008, 02:51:25
Well, if they do that, it means they have some electronic shutter on their CCD, or else they would have to flip their shutter 24 times a second in order to avoid the different exposure on different lines of the sensor.
yes, all of them has electronic shutter, without that live preview would be impossible...
many cameras has mech shutter because the electronic shutter efficiency is not 100%
electronic "shutter close" is a charge transfer(or something like this) from the photosensor to the ccd transmission line(which is deeper in the silicon wafer) i don't know exactly...
« Last Edit: 21 / May / 2008, 03:22:26 by dzsemx »
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #13 on: 21 / May / 2008, 04:06:57 »
No, not rally.
The live view is done at a much lower resolution than the sensor resolution, so many lines are skipped in the process.
Like both me and Microfunguy discovered, removing the shutter will cause the horizontal lines to have different exposure times, which deteriorates the image.
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Offline dzsemx

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Re: Converting the camera to prime focus
« Reply #14 on: 21 / May / 2008, 05:27:01 »
you discovered the backsides of the cheap/crappy ccd technology...
probably the transfer of charges can not be done correctly with ligth...
btw... there are digital cameras with ccd sensor completely without mechanical shutter...
« Last Edit: 21 / May / 2008, 07:40:26 by dzsemx »
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #15 on: 21 / May / 2008, 12:52:24 »
Are you sure there are such cameras? Can you give me an example?
Because I really want to get one.

Webcams do not count because they have fewer pixels, so it's possible to get them all very fast.
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Offline Microfunguy

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Re: Converting the camera to prime focus
« Reply #16 on: 21 / May / 2008, 13:39:38 »
Quote from: RaduP on 21 / May / 2008, 12:52:24
Are you sure there are such cameras? Can you give me an example?
Because I really want to get one.


So do I, I have never seen one.

If they do exist, I bet you cannot get fixed-focus non-zoom versions.

David
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Offline DataGhost

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Re: Converting the camera to prime focus
« Reply #17 on: 21 / May / 2008, 17:03:44 »
My cellphone (Nokia N80) has a 3 megapixel camera with no mechanical shutter. The only zoom it can do is digital and it has no focusing capabilities. Downside is that the quality is crappy, compared to my S5IS. With enough light, it'll still make decent pictures, though.
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #18 on: 21 / May / 2008, 23:53:02 »
Yes, and most likely it has a CMOS sensor. The CMOS sensors do not have this problem.
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Offline dzsemx

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Re: Converting the camera to prime focus
« Reply #19 on: 22 / May / 2008, 00:25:36 »
btw... probably you noticed that using preview mode, pointing the camera to a light bult, appears a purple-blue vertical line on the screen(also is there in movie mode)...
« Last Edit: 22 / May / 2008, 00:31:23 by dzsemx »
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