# curiosity concerning f number, focal length and aperture size calculations

Started Jan 26, 2014 | Questions thread
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curiosity concerning f number, focal length and aperture size calculations

Camera ... Panasonic GX1. Micro four thirds.

First of all, I do understand f numbers, well sort of! I'm very much a newbie in the manual settings arena, so to get a better understanding of the relationship between f number, focal length and aperture size, I've done some fairly basic calculations. From what I've read ...

F number = focal length / aperture diameter.

So 100 focal length / 25 gives f4.

Does this mean that focal length / f number = lens diameter? Maths has never been my strong point!

If so ...

I have a 28 - 84 focal length zoom lens with f3.5 to f5.6.(14 - 42 in micro four thirds)

At  28mm f3.5 this calcs to an aperture of 8mm in 35mm equiv

At  84mm f3.5 this calcs to an aperture of 15mm in 35mm equiv

Is this correct or am I struggling under a misconception?  If so can someone put me right?