Real focal length and online focal length calculators

Started Nov 5, 2012 | Questions thread
Andrew Westlake Senior Member • Posts: 2,928
Angle of view changes with focus distance

Focal lengths are specified at infinity, and can be used to calculate the angle of view for 'distant' subjects. Almost all lenses change their angle of view when focusing closer - in general primes normally get narrower, but zooms wider (and sometimes substantially so). If you've done your calculations right, you've discovered how much wider your camera's lens gets when focusing relatively close.

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Andy Westlake

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