Digital Photography Reviews, Articles, Tips and How-Tos

The aperture is the name given to the hole in the front of the lens that allows light to fall onto the film or the sensor when the shutter is opened. The size of the hole can be adjusted by means of a diaphragm that works just like the iris of your eye.

Increasing the size of the aperture allows more light into the camera and decreasing it allows less light. Along with shutter speed, adjusting the size of the aperture is one of two ways of adjusting exposure.

The size of the aperture is measured by the f-number, which represents the diameter of the aperture in terms of the focal length of the lens. So, for example, if you are using a 50mm lens and the aperture is set to f/4, then the diameter of the aperture will be 50/4 = 12.5mm.

Most camera lenses today use a standard scale of f-stops. Each possible aperture size is √2 (i.e. 1.4) times smaller or larger than the previous one. The scale is:

One step (or ‘stop’) along the scale means the amount of light reaching the lens will be halved.

You can also stop up or stop down by changing the shutter speed. One step in the scale of shutter speeds is equal to one stop of aperture size. This becomes important when considering the correct exposure for a shot.

The size of the aperture also effects the depth of field. The smaller the f-number, the smaller the depth of field and vice versa. Therefore in landscape photography, you often want to use the largest f-number you can, to ensure an image is sharp from front to back. However, a large f-number requires a slower shutter speed and therefore you may need to use a tripod to prevent camera shake.