Practice question · Numerical answer
A 35 mm lens is set to f/8 on the 24 by 36 mm format, with a circle of confusion of 0.03 mm. What is its hyperfocal distance, in metres, to one decimal place?
Hints
- Square the focal length, then divide by the f-number multiplied by the circle of confusion.
- 35 squared is 1225, and 8 times 0.03 is 0.24.
Show the answer
5.1 (answers within ±0.3 count)
Why
About 5.1 metres. 1225 divided by 0.24 is 5104 mm, and adding the focal length gives 5139 mm. Focused there, everything from about 2.6 metres to infinity is sharp by the 0.03 mm convention, which is why a 35 mm lens at f/8 was the standard pre-set for reportage.
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