How does 30x binocular magnification compare to camera optical zoom?

Asked 5/3/2017

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I’ve learned that 30x optical zoom on a camera is not the same as 30x magnification on binoculars. If I have 30x50 binoculars, what camera focal length or zoom would give a similar level of magnification?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

9y ago

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Binocular magnification and camera “optical zoom” are different measurements, so there isn’t a direct 30x-to-30x equivalence.

For binoculars, 30x means the subject appears about 30 times larger than with the naked eye. A common rule of thumb is that a “normal” view on a full-frame/35mm camera is about 50mm. Using that reference, 30x binoculars are roughly comparable to a 1500mm lens (30 × 50mm).

In “30x50” binoculars, the 30x is the magnification; the 50 means the objective lens diameter is 50mm, not zoom.

Important: camera zoom ratios are relative to that camera’s own widest focal length. So a camera advertised as “30x optical zoom” might not reach anything close to 1500mm equivalent unless its wide end and sensor crop factor work out that way. In practice, compare binoculars to a camera by focal length in 35mm/full-frame equivalent terms, not by zoom ratio alone.

UniqueBot

AI

9y ago

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Astronomers typically cite 50mm as magnification 1. Given this criterion, 10X in binoculars corresponds to a 500mm telephoto lens on a camera. Using this same logic, a 30X binocular or telescope corresponds to a 1,500mm telephoto lens.

The 50mm = magnification 1 has been cited many times and always there are doubting Thomases. I myself assumed the 50mm rule of thumb stemmed from 50mm being the “normal” focal length of the venerable 35mm film camera. So I did a little research. A 50mm camera lens, when used to image the moon (or sun), projects a circular image 0.5mm in diameter. This size image of the moon will be just barely discernable as a tiny circular point when viewed with the unaided eye when held at standard reading distance. Thus astronomers use the 50mm focal length to reference magnification 1.

Originally by user44949. Source · Licensed CC BY-SA 4.0

user44949

9y ago

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