fundamentals8 min read26 April 2026
Understanding f-stops: aperture, depth of field, and the full exposure triangle
Everything you need to know about aperture — from the physics of f-stop numbers to creative depth of field control and exposure relationships.
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What an f-stop actually is
An f-stop (or f-number) is the ratio of the lens focal length to the diameter of the aperture opening. f/2.0 on a 50mm lens means the aperture opening is 25mm wide. f/8 on the same lens means the aperture is 6.25mm wide.
This is why the numbers seem backwards: a larger f-number means a smaller opening, less light, and greater depth of field.
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