Portraits Affected With The Different Angle Of View And Focal Length Ratio

In most photography and all telescopy, where the subject is essentially infinitely far away and magnification is achieved by moving the image plane away from the center of projection, longer focal length (lower optical power) leads to higher magnification and a narrower angle of view; conversely, shorter focal length or higher optical power is associated with a wider angle of view. On the other hand, in applications such as microscopy in which magnification is achieved by bringing the object close to the lens, a shorter focal length (higher optical power) leads to higher magnification because the subject can be brought closer to the center of projection.
In photography
Camera lens focal lengths are usually specified in millimetres (mm), but some older lenses are marked in centimetres (cm) or inches.