cm m in ft m ft yd focal length mm     + scope x a b = mm ↑ 14.8 14.9 15 15.6 15.7 22.2 22.3 22.4 23 23.5 23.6 23.9 24 35.9 36 41.5 54 56 a/b =
          ( 75 %)

This calculator computes one of the following:

• animal (for example bird) or other photographed object size
• focal length of the lens
• distance from the camera to the photographed object
  (or rather object distance)
• camera sensor or film frame size
• photographed object image size : camera sensor or film frame size ratio
• spotting scope magnification (if used)

from the remaining parameters. It is not applicable for fisheye lenses.