Take your best shot

What’s ƒ about?

By Adrian Toon, director of a2n.

Photography can be confusing, and understanding the settings of your camera can go a long way to improving what you take. The ƒ number on your camera, SLR, compact or smartphone, is, in reality quite simple.

The ƒ number is simply a ratio, focal length/lens aperture diameter, where focal length is the distance from the back of the lens to the sensor. For example, on a 50mm lens with an aperture diameter (or iris) of 25mm ƒ would be 2.0. We can change the ƒ number on our cameras by using the settings; a larger number such as ƒ16 makes the aperture diameter smaller, so on the same 50mm lens, just 3.1mm in diameter.

Why is this important? A wider aperture lets more light onto the sensor, so good in low light, it also offers a shorter depth of field, which offers background or foreground soft focusing, or increased bokeh. A small aperture increases the depth of field so making close and distance objects appear more in focus. A pinhole camera for example has no lens, just a pinhole, so allowing very little light on a viewing screen, but with a focus across all distances from the camera.

Knowing your ƒ is crucial to understanding your subject and what you wish to achieve in your completed image. Next month we will look at speed and how this works with ƒ.