Practice question · Numerical answer
The 24 by 36 mm frame is the reference for calling a 50 mm lens normal. What is the diagonal of that frame, in millimetres, to the nearest whole number?
Hints
- Use Pythagoras on 24 and 36.
- 24 squared is 576 and 36 squared is 1296.
Show the answer
43 (answers within ±1 count)
Why
43 mm. The square root of 576 plus 1296 is 43.27. A normal lens is conventionally one whose focal length is near the diagonal, which puts 50 mm slightly on the long side of normal, the reason a 45 mm lens looks more like unaided vision than the standard 50 does.
Practise Lenses, Field of View and Depth of Field
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