What the heck is an “f-stop”?

An f-stop is a photographic term relating to the size of the aperture opening of a camera’s lens.

f-stops are typically numbers like this (“full” stops):  2.8, 4.0, 5.6, 8.0, 11.0, 16.0, 22.0, 32.0.

In modern digital SLR cameras (DSLRs), there are usually two f-stop numbers between each of the full stops listed above.  These other numbers are “third-of-a-stop” increments.

The wider the aperture, the smaller the f-stop number, the more light comes into the lens (and, the shallower the depth-of-field).

The narrower the aperture, the larger the f-stop number, the less light comes into the lens (and, the deeper the depth-of-field).

With regard to “full stops”, as an aperture number gets larger (by a full stop), half the amount of light comes through the lens. For example, an aperture of f/5.6 lets in twice as much light into the lens as an aperture of f/8.0.

Why do the smaller number represent wider apertures, you ask?

Because, an f-stop is actually a fraction.  For example, an aperture of 2.8 is actually written as f/2.8.  Therefore, the smaller the f-stop number, the larger the fraction, and the wider the aperture opening.

Hmmmm, perhaps David should create a blog post about this!

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