Focal length of a camera lens system is a measure of how strongly it converges (focuses) light. A photographic lens is used in a camera to make images of the opbjects on the film or other image sensors.
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Measurement of focal length is done in mm. nowadays:
- Wide-angle lens 18mm, 20mm, 28mm, 35mm
- Normal lens 50mm, 55mm
- Telephoto lens 90mm, 135mm, 200mm, 300mm