Jul 07 Explanation of Aperture

Aperture refers to the size of the opening that lets light through the lens into the camera’s sensor. One way picture aperture is to think of the iris of your eye. When you’re in a low light situation the iris of your eye will open all the way to allow the most amount of light in. When you’re outdoors in bright sunlight the iris of your I will close to limit the amount of light let in. The aperture of your lens is opened and closed with the use of aperture blades, these blades produce the same effect that the iris of your eye produces. Aperture can also be referred to as F stop, iris, and speed.

Aperture is normally measured in one of two ways either calculated speed or measured speed. Calculated speed is represented by an F and measured speed is represented by a T. Calculated speed uses a complex set of mathematical calculations to determine a lenses projected speed. Calculate speed is most often used in photography and SLR lenses. Measured speed is the actual measured amount of light allowed through a lens. Measured speed is most commonly used with cinema lenses.

By controlling the amount of light let in through the lens you are able to control the amount of focus depth, also known as depth of field. A wide aperture, such as 1.8, will have a very shallow focus depth. A narrow aperture, such as 22, will have a very deep focus depth. For instance, with your lenses aperture set to 1.8 and focused on a subject 10 feet away everything from 0 to about 9.5 feet will have soft focus and everything from 10.5 feet to infinity will have soft focus therefore you will have about 1 foot of focus depth. If you set your lens to an aperture of 22 everything from 0 to about 6.5 feet will have a soft focus and everything from 20.5 feet to infinity will have soft focus therefore you’ll have a focus depth of about 14 feet.

Aperture it’s not the only determining factor in controlling focus depth. The size of your cameras imaging sensor also has an effect on focus depth. For instance, a camera with a 35 MM sensor or using 35 MM film will allow you to achieve much shallower depth of field. A camera with ¼ inch image sensor, such as a consumer video camera, will have very little depth of field even if the cameras lens aperture is set to its widest open setting.

There are many resources to help you calculate depth of field particular lenses and cameras. One example of a depth of field calculator can be found at DOFMaster.com