_{This is no technical article about the focal length. If you want to read a very detailed article, have a look at the wikipedia article about focal-length.}

The focal length is measured in millimeters. This value is specified on any lens and stands for the part which will be photographed in a bigger/smaller resolution, depending on the focal length.

At a small value you can see much more in the photo than with a longer focal length. Focal lengths below ~50mm are called wide-angle lenses, which are mostly used on subjects such as Architecture Photography or Landscape Photography. Focal lengths below -24mm are called ultra wide-angle lenses.

Longer focal-lengths create a smaller field-of-view. The higher the focal-length is, the farther away your subject will be (comparable to using a telescope or binoculars, which also have a longer focal-length).

_{Yes, that’s me in the picture. Quite some time ago though ;)}

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