Lenses for network video cameras

Auto iris (DC and video)

There are two types of auto iris lenses: DC-iris and video iris. Both have a motor-driven, automatically adjustable iris opening that responds to changes in light levels. Both types use an analog signal (often the video signal) to control the iris opening. The difference between the two is where the circuitry to convert the analog signal into motor control signals is located. In a DC-iris lens, the circuit resides inside the camera; in a video iris, it is inside the lens.

In brightly lit situations, a camera with an auto iris lens can be affected by diffraction and blurring when the iris opening becomes too small. This can be particularly prominent in megapixel and HDTV cameras, as the pixels in the image sensors are smaller than in lower resolution cameras. Therefore, the image quality is more dependent on controlling and obtaining the correct iris opening (aperture). The problem with an auto iris lens is that this control is not available to the camera or the user.