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Old Oct 11, 2002, 11:28 AM   #1
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Default another newbie question regarding S200 (or cameras in genera

I got the Canon S200 a couple weeks ago, and as a newbie to real photography (no more $8 disposable cameras for me!) I have of course been messing around with all the features on settings on it. One thing I screw around with is the ISO-- there's 50, 100, 200, and 400. Whenever I take a picture with a higher ISO (specifically 400), it always produces a very granular picture. It's basically to the point where anything I take at 400 is pretty ugly, making 400 seem kind of worthless.

Is there something I'm missing? Are there other settings I have to adjust to compensate for the higher ISO to produce less granular pictures, or certain types of scenes I'm not aware of that higher ISOs should only be used for? When exactly do I use such a high ISO? The manual doesn't exactly go into such detail.
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Old Oct 11, 2002, 11:30 AM   #2
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Damn thread title character limit, and damn inability to edit posts. :-|

"...point of high ISOs when they produce such granular photos"
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Old Oct 11, 2002, 2:33 PM   #3
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This can be a bit tricky to explain without going into the quantum nature of light or the "you can't get something for nothing" clause of the second law of thermodynamics.

Basically put for most things you adjust on a camera you're trading one property for another. This is true of film/CCD sensitivity. If you don't ask for a lot of sensitivity it literally takes more photons to make an exposure. All those photons fill in the gaps so to speak and overwhelm the inherent noise in electronics. If you ask for ultra high sensitivity you'll be using fewer photons, less light information, which makes a less coherent image. Also the small number of photons are less able to rise above the background noise in the CCD.

Physically bigger cameras are able to use higher sensitivity media with less noise and still make smooth image. This is true of DLSRs and large format film cameras.

You can use post production methods to reduce noice but as a general rule this will come at the expense of sharpness and image detail.
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Old Oct 11, 2002, 3:19 PM   #4
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Ahh, ok then. Thanks. I guess I just needed a better understanding of what the ISO is. So you're saying it's the physical size of the camera (or lense, I take it) that results in more or less granularity? Will all pictures under any condition have a real granular look at ISO-400 with this camera?

It just makes me wonder why the camera is capable of such a high ISO when I have yet to take a picture at 400 that turns out decent looking in terms of picture quality.
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Old Oct 11, 2002, 4:07 PM   #5
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Have you tried to downsize those pictures to a small web size, say 90x120 pixels? With good downsizing software, the noise will "average" out and you will have a picture at that resolution which is just fine.

Perhaps not what you bought the camera to do, but it can be usefull to be able to get even low resolution pictures in low light.

But I think the real reason cameras have a basically useless ISO settings is for advertising. Pretty much the same reason cameras advertise digital zoom. Without the high ISO settings you can do much the same thing by underexposing by two stops, then expanding the histogram with levels adjustments to achive an ISO of 400. A bit more subtle than cropping, but the same issue.
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Old Oct 12, 2002, 8:12 AM   #6
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Perhaps the analogy is to film cameras. ISO rating I believe suplimented the more familiar ASA rating, and is exactly how much light is needed to get an image. Anyone who fooled around with Tri-X film knew that you could "push" the film in development to get it to produce an image with less light, but at the expense of getting more grain; more exactly you wanted several particles of the photosensitive silver to "clump" so as to improve the chance of one being changed by being exposed to light producing an image .I expect when they started digis they had a similar effect and called it ISO so as to be familiar to film users.
Padeye I think explains much else. What I don't know is if at higher ISO the digi purposely "pools" several photosensors for the same reason; to improve the chance of capturing a photon and producing an image,albeit a grainer one.
Phew!
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