Aperture
Aperture is put in with the mechanical section because it is a mechanicl function of the lens. Knowing about what it controls—depth of field—is perhaps more important than knowing any esoteric information about the aperture, but here we are.
At it’s most simple, the aperture is the hole in the camera that allows in light. It is not the shutter, which is a seperate mechanism which controls how long the aperture remains open. Fixed aperture cameras use apertures where the opening size does not change. Many point and shoot cameras, and pinhole cameras are fixed aperture.
Aperture Size
Aperture size is described by the ƒ-stop, or ƒ-number. This is actually a ratio of the focal length of the lens divided by the effective aperture diameter (the actual opening diameter). This means that an ƒ-number is relative to the focal length of the lens. In plainer English, ƒ/4 for a 50mm lens has a different actual opening than ƒ/4 for a 100mm lens.
Because the ƒ-number is a ratio, the numbers can be confusing to the beginner. The larger number means the smaller opening, so ƒ/22 is smaller than ƒ/8. The standard range of ƒ/numbers are:
| Standard ƒ/numbers or ƒ-stops |
|---|
ƒ/1.4, ƒ/2, ƒ/2.8, ƒ/4, ƒ/5.6, ƒ/8, ƒ/11, ƒ/16, ƒ/22, ƒ/32 |
There are plenty of lenses which have more or less than this list, but these are the most common. Very important to remember is that each number represents an opening that is half or double the preceding of following in opening size. Thus, ƒ/8 is twice the opening size of ƒ/11, and half of sƒ/5.6.
Controls
On manual cameras, the aperture size is controlled by moving the aperture ring on the lens. Generally the lens has detents (or stops) at the standard ƒ-numbers. Newer cameras will often have electronic controls of the aperture, some kind of dial or button that you manipulate to change the setting. Both types allow for “in-between” settings, with the electronic usually giving you 1/3 stops, and the manual giving you a best guess.
