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06-21-2010, 06:18 AM   #1
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K7 - k20d iso

Is there any real benefit in using the extended ISO and shooting @ ISO100.

06-21-2010, 06:28 AM   #2
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I believe the only real benefit would be allowing you to get a one stop faster exposure, this would come at the expense of dynamic range. Since iso200 is the native ISO of the sensor, the dynamic range is at its' largest when shot at the native sensor iso of 200. That is my limited understanding of it anyway!
06-21-2010, 10:09 AM   #3
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I believe both the K-7 and K20D have a native ISO of 100 whereas the K-X has a native ISO of 200. The benefit of shooting at ISO 100 is that you can use a larger aperture of longer shutter speed if necessary for your shot. Native ISO 100 is also cleaner/less noise than ISO 200. Extended ISO 100 on the K-X has a decreased dynamic range, and maybe more noise than ISO 200 (not sure) but the same benefits for aperture and shutterspeed.
06-21-2010, 01:30 PM   #4
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Ed, K20D has native ISO of 100, not extended .

06-22-2010, 09:43 AM   #5
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I believe the extended ISO ranges are essentially using PP to push or pull the image by a stop. So, the camera takes a picture at ISO 200 and then pulls it down a stop. I imagine that this could have a negative impact on dynamic range, particularly in the highlights, although noise shouldn't be affected when you are extending downward.

Although I do believe that ISO 100 is native for both the K7 and K20. In fact, I'm pretty certain it is because Pentax's in-camera highlight correction lowers the ISO by a stop and then pushes it in order to make sure more of the high end is captured. This would explain why ISO 200 is the lowest option when highlight correction is turned on, and indicate that 100 is probably base sensitivity.
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