Understanding Your Camera F-Numbers

If you have a camera then more than likely you have seen the numbers on your camera lens. These are referred to as f-numbers or f-stops. F-Number, also known as a focal ratio, is the ratio of the diameter of the lens aperture to the length of the lens. On most cameras, you can change the f-number by changing the f-stop setting on the camera’s lens. An f-stop represents a halving or doubling of the amount of light allowed through the lens, by halving or doubling the area of the aperture opening.

The more light the lens allows into the camera, the faster the shutter speed should be set, so as not to overexpose the film. Most camera lenses have f-stops that are represented numerically by integral powers of the square root of two. Common f-numbers on a lens are f/1, f/2, f/4, f/8, f/10, and so on. Most cameras allow the aperture to be adjusted by less than a full stop as well, typically allowing them to be adjusted by 1/2 or 1/3 of an f-stop. Similarly, the shutter speed and ISO on most cameras can typically be adjusted in 1/3 stop or 1/2 stop increments. This can provide more flexibility when adjusting camera settings.

DSLRs probably have the widest choice of f-numbers and allow the most adjustments. DSLRs default to 1/3 stop aperture and shutter speed increments. DSLRs should be set to full-stop increments if possible, 1/2 stop increments if full-stop increments are not available.

We hope this article gives you a better understanding of f-numbers and f-stops.


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