When shopping for a camera (or a new lens), one of the first few specifications listed is the maximum aperture, or aperture range. Aperture is defined here, briefly. So what does this mean to you?
A camera collects light. That’s how it makes pictures. The aperture of a lens is the size of the opening, usually controlled by an iris, also referred to as the diaphragm. The larger the opening is, the more light reaches the film, or the image sensor. Aperture is usually shown as an f-stop, for example F2.8 or f/2.8. The smaller this number is, the larger the lens opening (aperture) is. Some camera manuals will refer to an aperture value, this is simply another way of saying “f-stop or f/value. When shopping, this value will either be expressed as a maximum aperture, an aperture range (minimum and maximum aperture), or wide angle and telephoto apertures. That last way of expressing aperture gives the maximum value for wide angle, and the maximum for telephoto, not the minimum and maximum.
A “fast” lens is one that has a large maximum aperture, f/2.0 for example. Remember, the smaller the f-stop number, the larger the aperture is. A very good aperture range to have is f/1.8 – f/16. This means that the camera has a minimum aperture of f/1.8 and a maximum aperture of f/16.
Aperture and Depth of Field (DOF)
The depth of field is the distance in which objects are in focus. There are times where you would want a large depth of field, meaning objects close to you and far away from you would be in focus. This is especially true in cases like landscape photos, where you want as much area of the photo as possible in sharp focus. Other times, when you want to isolate the subject of the photo, like in a portrait, you want your subject to be sharp, but you would want the background out of focus, so you would need a shallow depth of field. You can influence this by selecting the appropriate aperture.
A general rule of thumb is that setting a large aperture (small f/value) like f/2.8 will give you a shallow depth of field. A small aperture (large f/value) like f/8.0 will give you a great depth of field.