Camera Lens Aperture Overview

Here is another learning series article and video. This time I go over the camera lens aperture.

Youtube video link:

The camera lens aperture is the variable opening inside the lens that lets more or less light into the camera. A small aperture has a larger number.

See a full technical description of aperture on Wikipedia:

Also important is the f-number that explains what the aperture number means:

f-number = focal length / diameter of the entrance pupil

So if we want to know the entrance pupil size of an 100mm f4 lens we calculate it like this:
diameter = 100 / 4
Giving us a 25mm front lens element.

An 85mm f1.4 lens results in a 60.7mm front lens element (85 / 1.4 = 60.7143).

The most important statement I didn’t cover in the video is “the aperture determines how collimated the admitted rays are,” so a small aperture has very collimated rays of light getting through to the camera’s sensor.

A large aperture (f1.4) will give you less depth of field (distance of perceived sharpness), and a smaller aperture (f22) will give you a larger depth of field.

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