Wedding, Portrait and Commercial Photographers 
Fig 1. Diagram of decreasing aperture sizes (increasing f-numbers)
for "full stop" increments (factor of two aperture area per stop)
A device called a diaphragm usually serves as the aperture stop, and controls the aperture. The diaphragm functions much like the iris of the eye, it controls the effective diameter of the lens opening. Reducing the aperture size increases the depth of field, which describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. In general, the smaller the aperture (the larger the number), the greater the distance from the plane of focus the subject matter may be while still appearing in focus.
Fig 2. Wide Aperture (Background blurred)
Fig 3. Small Aperture (More of image within focus plane) - Known as greater "Depth of Field"
The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter. A lens typically has a set of marked "f-stops" that the f-number can be set to. A lower f-number denotes a greater aperture opening which allows more light to reach the film or image sensor. The photography term "one f-stop" refers to a factor of √2 (approx. 1.41) change in f-number, which in turn corresponds to a factor of 2 change in light intensity.
Aperture priority is a semi-automatic shooting mode used in cameras. It allows the photographer to choose an aperture setting and allow the camera to decide the shutter speed and sometimes ISO sensitivity for the correct exposure. This is sometimes referred to as Aperture Priority Auto Exposure, A mode, Av mode, or semi-auto mode.
The specifications for a given lens typically include the minimum and maximum apertures.
These refer to the maximum and minimum f-numbers the lens can be set at to achieve, respectively.
A typical lens will have an f-number range from f16 (small aperture) to f2 (large aperture) (these values vary).
The maximum aperture (minimum f-number) tends to be of most interest (and is always included when describing a lens). This value is also known as the '''lens speed''', because it is proportional to the square of accepted light, and thus inversely proportional to the square of required exposure time (i.e. using a lens with f/2, one can take pictures at one quarter of the exposure time necessary using a f/4 lens).
Prime lenses have a fixed focal length (FFL) and large aperture and are favored by professionals, especially by photojournalists who often work in dim light, have no opportunity to introduce supplementary lighting, and need to capture fast breaking events.
Zoom lenses typically have a maximum aperture (minimum f-number) of f2.8 to f6.3 through their range. A very fast zoom lens will be constant f2.8 or f2, which means the relative aperture will stay the same throughout the zoom range. A more typical consumer zoom will have a variable relative aperture, since it is harder and more expensive to keep the effective aperture proportional to focal length at long focal lengths; f3.5 to f5.6 is an example of a common variable aperture range in a consumer zoom lens.
Posts
All Comments
