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Old May 5, 2004, 9:59 AM   #1
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Hi,

The Pentax lens quality on the small Optio S series has been under discussion (also used by some Casio models). From my world of SLR photography, it is a known fact that the best optical *resolution* is obtained when the lens is working on its mid aperture. E.g. a f1.4 50mm lens, with maximum aperture f1.4 and e.g. minimum aperture f16 will have best resolution at f4.0-5.6 approximately. (Note that resolution has nothing to do with depth-of-field). So, I tested the S4i to see what minimum paerture I could get, since it is not documented. I could not force the camera to provide a higher f-number than f4.3 at wide angle and f7.7 at telephoto. Since minimum f-number is f2.6 and f4.8 respectively, this means that the lens will always work at or close to full aperture. This is probably not good.

However, I don't know if the other small digi-cameras have more f-stops. And possibly, my comparison to SLR lenses are not adequate either. Anyone else having opinions on this subject?

Arne
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Old May 26, 2004, 9:12 PM   #2
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I've posted in another thread disappointment that the larger aperture is always used unless the scene is quite bright. In other words there is no way to forcethis toyto use the small aperture in low light in order to increase depth of field. The f-stop is a simple mathematical ratio between the aperture diameter and focal length. Since there is apparently just one stopped down diameter in addition to wide open the shown f-stop varies as the focal lenth is zoomed. But the actual size remains constant. Thus there is no "middle" to stop down to.
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Old May 27, 2004, 4:32 AM   #3
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Your observations are the same as mine, there are only two f-stops. This might be usual on such small lenses, since aperture diffraction might result in even smaller apertures. ON such small focal lengths the depth-of-field is always large, except when focussing at small distances (as one can see with the super macro).

I your case with graph paper you hight have a problem with focus dept-of-view at corners since I assume the distance to the paper is not that much. However, the camera is soft in corners also at large distances. But not more than one should expect perhaps.:O

Arne
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