I just recently learned that 30x Optical Zoom on a Camera and 30x Magnification on Binoculars are different things.
Suppose if I have got 30x50 Binoculars, then what would be its equivalent number of an Optical Zoom that I can expect?
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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.