pub fn shutter(num: u32, denom: u32) -> StringExpand description
A shutter speed the way a camera’s own screen shows it: a fraction
under a second (1/500), seconds from there up (0.3s, 2s).
A camera often stores 10/5000 rather than 1/500, so the fraction
is reduced — but only when that lands on a whole denominator. 3/10
is not a stop anyone dials in as 1/3.33.