Aperture
Aperture is how wide the lens iris opens.
The wider it opens the more light gets in. It’s the same as the human eye, the
less light the more the iris needs to be open, to allow more light in, and the
more light, the smaller the iris, as less light is needed.
The lens controls the amount of light they
let pass through to the film of video receptor. Bigger apertures and smaller
numbers, like f/4, and smaller apertures have bigger numbers like f/16. These
numbers are called the f/stop and this is the mathematical relationship of the
overall size of the lens to the size of the aperture.
The f/stop (or stop) is a unit of light
measurement. An increase in the amount of light by one stop means there is
twice as much light. Subsequently a decrease of one stop means there is half as
much light. Every time the aperture is increased by one whole stop, the quantity
of light reaching the film is doubled. The f/stop is the ratio of the focal
length of the lens to the diameter of the entire pupil. Thus, each stop is
greater than the previous by the square root of 2, which in turn corresponds to a factor of 2 change in light intensity.
f/stop = focal length/ diameter of lens
opening
OR
f= F/D
F/stop numbers are fractions, with the
relationship f = F/D. so for example f/16 really means 1/16;
the diameter is 1/16 focal length. And f/8 is 1/8
, which is a larger fraction than 1/16, so the size
of the iris is wider for f/8 than it is for f/16. Think of it as the larger the
f/stop number the smaller the iris opening, and the smaller the f/stop number
the wider the opening.
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