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APPENDIX A: GLOSSARY
APPENDIX A
Glossary
Terms and definitions
Term
Definition
AGC
Automatic Gain Control, an electronic circuit that amplifies the video signal when the strength of the signal falls below a given
value.
ALC
Photometric control, measures light intensity. Determines the iris reaction sensitivity. Sensitivity is increased when the potentiom-
eter is turned towards PEAK, and decreased when turned towards AVERAGE.
APERTURE
The opening of the lens which controls the amount of light reaching the surface of the pickup device. The size of the aperture is
controlled by the iris adjustment.
APERTURE SCALE
The aperture scale is referred to as a F-number. The international aperture scale is: F1, F1.4, F2, F2.8, F4, F4.6, F8, F11, F16, etc.
AUTO-IRIS LENS
A lens with a electronically controlled iris. This allows the lens to maintain one light level throughout varying light conditions.
BLC
Back light compensation. A function of the camera that compensates for excessive light directed at the camera causing the video to
bloom or causing the images in front of the light to be unusable.
CAMERA FORMAT
The approximate size of a camera image pickup device. This measurement is derived from the diagonal line of a chip or the diameter
of the tube. Currently there are five format sizes in the CCTV industry 1”, 2/3”, 1/2”, 1/3” and, 1/4”
DC TYPE AUTO-IRIS
Auto-iris lenses where the iris is controlled by the circuitry of the camera.
DEPTH OF FIELD
The regions in front of and behind the focused distance where the image remains in focus. With a greater the depth of field, more of
the scene near to far is in focus. Lens aperture and scene lighting will greatly influence the D.O.F.
F-NUMBER
Indicates the brightness of the image formed by the lens, controlled by the iris. The smaller the F-number the brighter the image.
FIELD OF VIEW
The horizontal or vertical scene size at a given length from the camera to the subject.
FOCAL LENGTH
The distance from the center of the lens to a plane at which point a sharp image of an object viewed at an infinite position. The focal
length determines the size of the image and angle of FOV seen by the camera through the lens. This is the center of the lens to the
image pickup device.
HUNTING
An industry term used to describe a auto-iris lenses inability to stabilize under certain light conditions.
IRIS
A mechanical diaphragm which can be controlled manually or automatically to adjust the lens aperture.
LENS FORMAT
The approximate size of a lens projected image. In most cases the lens will project a image slightly greater than the designated
image size to insure the pickup device is completely covered. It is recommended that camera and lenses are the same format size. A
lens a larger format size can be used on a smaller format camera, however a smaller format lens should never be used with a larger
format camera.
LEVEL CONTROL
Used to set the auto-iris circuit to a video level desired by the user. Turning the level potentiometer towards the HIGH position will
open the iris allowing more light to pass through the lens, towards the LOW will close the iris allowing less light to pass through
the lens.
MANUAL IRIS LENS
A lens with a manual adjustment to set the iris opening (aperture) to a fixed position. This type lens is generally used in fixed
lighting conditions.
TELEPHOTO
Telephoto is a term used to describe lenses that have a high focal number causing the reproduced image to appear larger than
human eye reproduction.
VARIFOCAL
A low cost version of a zoom lens designed to meet installers needs for versatility. This lens does not have the ability to track from
wide to telephoto.
