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Old Aug 24, 2005, 11:26 PM   #1
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I was bored;

5 photos; ISO Auto, 50, 100, 200 and 400. Untouched other than photos resized from 4MP to 1000x750. For info; the Auto setting actually chose the 200 ISO setting. http://www.pbase.com/ajuett/iso_test
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Old Aug 25, 2005, 12:48 AM   #2
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not sure what you are looking for in the way of critique...
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Old Aug 25, 2005, 8:54 AM   #3
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Not quite sure what you are trying to demonstrate either. Generally an ISO test would compare noise levels but it looks more like you are comparing exposure differences. If you are shooting for noise levels then shoot in AV mode in each ISO setting, using the same aperture. This way the camera will set the shutter speed and each image will come out with similar exposure and the noise levels can be compared.
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Old Aug 25, 2005, 10:06 AM   #4
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This forum is really where members come to ask for critique about a specific photo, not for comparing noise levels, etc. So, I'll move this thread to the Pentax forum, where you may get comments.

It's not clear what you are trying to accomplish. But, you're seeing exposure differences because the first few photos are underexposed.

If I had to guess, the camera's autoexposure is using a slowest shutter speed of 1/4 second by default in the mode you were in. Because that shutter speed is too fast for the lighting conditions at lower ISO speeds, you're seeing underexposed photos until the ISO speed is set higher.

If light was better, you'd see the same exposure, regardless of ISO speed. There may be a mode that allow your camera to go slower than 1/4 second, too. You'll need to look in your manual to see. That way, you'd have correct exposure at any ISO speed if the camera could use slower shutter speeds (and I don't know if it can or not).


OK, I see from the EXIF your camera was in shutter priority mode (I didn't realize the little Pentax model had this). So, you had the shutter speed set too fast for proper exposure of the images for the lighting conditions. Your manual should explain how the camera metering lets you know if your settings are gong to result in underexposed images (sometimes with a flashing aperture/shutter speed, with a meter scale showing underexposure, depending on the camera model).

If you set the camera to a shutter speed faster than the lighting conditons, ISO speed, and largest available aperture allow (and the value may or may not flash to let you know it, depending on the model), you'll get underexposed photos.

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