FOVtofocal lengthcalculator

Converging (convexcloseconvexAn object or shape that curves or bulges outwards, like a circle or sphere.) lenses have positive focal lengths, so they also have positive power values.

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fov和焦距的关系

If a lens has a shorter focal lengthclosefocal lengthThe distance between the centre of the lens and the focal point. it is said to be more powerful. The power of a lens is defined as the reciprocalclosereciprocalThe reciprocal of a number is 1 divided by that number. The reciprocal of a fraction is that fraction turned upside down, eg the reciprocal of 3/4 is 4/3. of the focal length. Lens power is measured in dioptres (D).

FOVtofocal length

I understand why focal length is a stand in for field of view most times. Just having a short hand of the lower the focal length, the wider the shot, and vice versa is intuitive and easy for beginners. But with crop sensors at some point you have to learn how to disambiguate true focal length from field of view (effective focal length).

Lenses are precisely shaped pieces of glass that have been developed and used in corrective glasses, telescopes, microscopes, binoculars, and magnifying glasses.

Diverging (concavecloseconcaveCurving inwards, rather than bulging outwards.) lenses have negative focal lengths, so they also have negative power values.

But between.... DSLR and interchangeable lens mirrorless cameras and your smartphone, focal length is kinda confusing. I understand why focal length doesn't change between FF and crop sensor cameras because I get that those are describing the actual focal length. And I get that when smartphone manufacturers talk about the zoom range of their cameras, they are probably using focal length as a proxy for field of view. You can just look at a phone and see that that 200mm focal length is not feasible. But what about bridge cameras? What about 1-inch sensor cameras? What does the focal length describe on those cameras?