Fixed or adjustable iris
The ability to control a camera’s iris opening plays an important part in image quality. The iris maintains the light level reaching the image sensor at an optimum, so that images are sharp, clear and correctly exposed, with good contrast and resolution. The iris can also control the depth of field. Iris control can be fixed or adjustable. Adjustable iris lenses can be manual or automatic (auto iris and P-Iris).
In indoor environments where light levels can be constant, a lens where the iris is fixed at a certain f-number can be used. However, the camera can also compensate for changes in the light level, by adjusting the exposure time or the gain setting.
A manual iris lens is adjusted by turning a ring on the lens to open or close the iris. This is not convenient in environments with changing light conditions, such as in outdoor surveillance applications.