Understanding Apertures

The size of the aperture, iris, hole (it's referred to in different ways) which light passes through to reach the sensor can be controlled by you to allow more or less light into the camera. The aperture is measured in f numbers (often referred to as a 'stop' or 'stops'). The largest holes have small (low) numbers like f2.8 and f4 and the small holes have bigger (higher) numbers like f22, f16.

The full list of f numbers is as follows:

f1.4, f2, f2.8, f4, f5.6, f8, f 11, f16, f22, f32, f45, f64. Where this sequence starts or finishes depends on the lens in use.

So, what do all these f numbers mean and where do they come from?

Aperture is regulated in a 2:1 ratio so that each f number represents a doubling or halving of the size of the hole and therefore the amount of light which is allowed to pass though and onto the sensor. For example, f8 provides a hole which is twice the size of f11 and the f11 hole is twice the size of f16, which means that twice as much light passes through the aperture at f11 than it does at f16. Conversely, f8 receives half as much light as f5.6.

Remember, big numbers like f22 have a small hole;low numbers like f4 have a large hole.

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