P-Iris is a new type of iris control that is both automatic and precise. The primary objective of P-Iris is to improve image quality by enabling the optimal iris position to be set so that the central and best-performing part of the lens is used most of the time.

With P-Iris Lens

Without P-Iris Lens

Drawback of DC-Iris in Automatic Mode

The iris of a lens regulates the size of a lens’ aperture or opening and the amount of light that passes through it so that an image can be correctly exposed. Without an iris, an image can become too light in a very bright environment, or it can be dark if the lens opening is not big enough to let available light in.

Iris Size, Intensity of Light and Depth of Field

The size of the iris opening also has an effect on image sharpness and depth of field. A wide iris opening reduces depth of field while a smaller opening increases it. Image sharpness generally improves with a smaller iris opening because optical errors can often be reduced. All lenses create some form of image aberrations when the full lens surface is used.

The size of the iris opening also has an effect on image sharpness and depth of field

While it is true that a smaller iris opening often means sharper images, too small an opening may blur an image due to an optical effect called diffraction. This problem can be seen in bright outdoor situations when a camera closes the iris too much and light is diffracted or spread over many pixels. The smaller each pixel is on an image sensor, the more of a problem diffraction becomes as the diffracted light affects more pixels. This can typically happen in cameras that use an automatic DC-iris lens in combination especially with megapixel sensors that have small pixels. (While a megapixel sensor has more pixels than a standard VGA 640×480 image sensor, the size of each pixel on a megapixel sensor is often smaller than the size of each pixel on a VGA image sensor.)

Too small an opening may blur an image due to an optical effect called diffraction

With P-Iris Lens

The system comprises of a P-Iris lens and specialized software in the camera. The software steers a motor in the P-Iris lens, enabling automatic and precise control of the iris opening. The key to understanding P-Iris is to look at how the iris affects image quality.

Working in conjunction with P-Iris is the use of electronic means—gain (amplification of the signal level) and exposure time—to manage slight changes in lighting conditions and to further optimize an image. This allows the optimal iris position to be maintained as long as possible. In situations when the preferred iris position and the camera’s electronic processing capabilities cannot adequately correct the exposure, a P-Iris camera will automatically instruct the iris to move to a different position. In dark conditions, for example, the iris will fully open. In bright situations, a camera with P-Iris is programmed to limit the closing of the iris to a position that avoids diffraction or blurring, as explained earlier. Hence, in all lighting conditions, P-Iris can automatically make adjustments to deliver optimal image quality.