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where is the sharpest f-stop for landscape?


chi_siu1

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It depends what you mean by "sharpest f-stop". I am principally a photographic landscapist using 8x10, 4x5, and roll film cameras and the challenge is usually not getting the "sharpest" image but rather getting an image with the most "detail" in it. Another somewhat more abstract way of putting this is to make photographs with the "maximum visual information content".

 

Landscapes are usually 3-dimensional subjects with a lot of front to back depth. As a lens is stopped down its maximum resolution decreases because of image diffraction. At the same time the increased depth-of-field makes more things, front to back, look sharp rather than blurry. These two effects, increased diffraction (bad) versus increased depth-of-field (good), work against each other. There is an optimum balance between these contending effects and it depends on the final enlargement size of the photograph. Here's my rule:

 

If the final image is a 8" X 10" photograph then the aperture iris of the lens should have a diameter of 3 millimetres. For other enlargements the required aperture diameter changes proportionately, 6mm for a 16" X 20" photograph, 1.5mm for a 4" X 5" photograph, and so on .....

This rule applies to all my cameras from 8x10 to 35mm. Note that with a normal 300mm lens on a 8x10 camera a 3mm aperture diameter means the lens is working at f100. A 50mm lens on a 35mm camera is at f16 for the same 3mm diam. aperture. The reason the rule works is that at the optimum aperture the depth of field is maximised but the blurring effects of diffraction are just below the threshold of visibility.

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How about the same question when the camera is handheld and not using a tripod ? Thanks

If the camera is handheld at *slow* speeds, the gain in sharpness due to a "better" aperture could be lost via camera shake, so it could also result in some kind of softness (let`s put aside DoF considerations).

Whether if better results are achieved handheld&optimal aperture, or on a tripod&diffraction limited, I`d say it will depend on the amount of shake and on the amount of diffraction (airy disk size).

If I have to choose, I`d ask for a tripod. The safe zone where both options are equalized seem too narrow.

Edited by jose_angel
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