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Old Dec 11, 2003, 6:27 AM   #1
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Default 2 GB Ridata Card question -Affect of ASA on # of images

I was shooting a high school wrestling competition last weekend when I noticed something odd. I was shooting at L Jpg as usual on my 10D and when I started I formatted my 2Gb Ridata card to get all the old images off of there before I began shooting. Usually when I do that it tells me have 760+ images available to shoot at that setting, this time it told me I only had about 540 or so. I was shooting at 800 - 1600 ASA in the gym.
The next day when I was shooting a horse show and changed the ASA to 100, it bumped up my number of images available !
How does your ASA setting affect your number of images you can shoot on a card?
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Old Dec 11, 2003, 8:35 AM   #2
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as you climb higher in the ISO realm the camera performs a dark slide shot automatically for subtractive noise reduction. the higher the iso the bigger they are. this takes up room too on the cf card. hence you get less shots.

in sort your taking 2 shots for the price of one. just one looks black.

wow i haven't heard ASA for a while.
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Old Dec 15, 2003, 9:16 PM   #3
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I don't think the 10D does the second shot. That was a feature of the D30. Higher ISO has higher noise levels, which can't be compressed as much by the jpeg algorithm.
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Old Dec 16, 2003, 7:24 AM   #4
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the 1Ds does it too. upping the ISO will cause this also. dark slide/image subtraction i believe is used too.
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Old Dec 16, 2003, 2:21 PM   #5
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Default number of images

JPG images have a great range of file sizes even when using the same settings. When shooting coins on a plain black background, I often get over 200 images on a card that the camera suggests is good for 150. The reason is that the camera had no way of knowing I would be using so many zero value areas so large in size. I even recall the suggestion that file size is a good way to select the sharpest image of a series of like shots since the camera will have to use more space to save the fine detail. Is that correct or an old wives' tale? It makes perfect sense that a lot of noise would be read as a lot of detail and make a larger file. Does anyone have any ISO 800 shots made with a noisy camera (Minolta?) to compare with a 'quiet' SLR? I'm wondering if it is possible that an optimum 6Meg image might even end up being smaller than a noisy 5Meg? Pretty obviously the camera considers the ISO setting when estimating the image count remaining but that is certainly nothing more than an estimate.
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Old Dec 19, 2003, 11:03 AM   #6
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Higher ISO (we don't say ASA anymore, at least not for the last 10 or 15 years) images are noisier - noisy images do not compress as well as lower ISO "smooth" images. That's all there is to it.

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Old Dec 19, 2003, 4:27 PM   #7
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According to Chuck Westfall (Canon USA) the 10D does not use the subtractive method of eliminating noise, as other cameras do.

Higher ISOs use more space because of the higher level of noise. These images don't compress as well in jpeg.
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