[Photography] Smallest and highest F-number


Summer time in Switzerland
View from Top of Europe, Switzerland


Fun fact: the smallest F-number is defined by the quality of your lens (hence its price), but the highest F-number is an intrinsic property of the camera itself.

Here is why:

As mention in this article , the F-number is defined as the ratio of the lens’s focal length to the diameter of its aperture. The the focal length of a length, as well as its effective aperture, do not depend on the camera. The focal length change with the curvature of the glass, and it is not very hard to customize a curvature; but it is extremely difficult to create a large-scale lens with highly-defined curvature (mostly because lenses are made from glass). As consequence, the price of a lens increases exponentially with their minimum F-number.

Once the lens is set into the camera, then with a fix focal length, the largest F-number corresponds to the smallest aperture that the camera allows. The aperture of a camera is controlled mechanically by its iris (similar to that in the .gif file below from Wikipedia). Because of a relatively simple mechanism, even low-end camera can feature high F-number. High F-number results in higher depth of field (as explained in this article). Nevertheless, it doesn’t really matter anyway, because one cannot easily distinguish the image quality a photo taken with F-number = 20 above or F-number = 16 below.

The Proud Mattenhof
Mount Matterhorn, Switzerland

Related fact: the smallest F-number a lens can enable, the “faster” and more expensive it is. (explained here).


Iris Diaphragm.gif



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