GLOSSARY OF TERMS
APERTURE
– An opening or hole through which light passes. In the optical system it is equal to the diameter of the
largest entering beam of light that can travel completely through the system. This may be equal to the front lens of the
objective.
MAXIMUM APERTURE
– The largest size to which the iris diaphragm of the lens can be opened. (The lowest f-number)
IRIS
– The lens “iris” is a mechanical device for controlling the lens aperture (lens opening). A lens may be fixed, manual
controlled and / or voltage controlled.
AUTOMATIC IRIS
– An iris that automatically adjusts to control the light reaching a sensor to compensate for light level
changes.
“C” MOUNT
– A television industry standard for lens mounting, which has a 1 – inch diameter, threaded barrel and 32
threads per inch. The sensor is located 0.69 inches behind the mounting surface.
“
CS” MOUNT
– A television industry standard for lens mounting, which has a 1-inch diameter, threaded barrel and 32
threads per inch. The sensor is located 0.492 inches behind the mounting surface.
BACK FOCUS
- A term used to describe the relationship of the distance of the lens iris (aperture) to the imager device
(CCD chip). This distance is critical to maintain proper depth of field through changing focal lengths and varying light
conditions. The back focus is achieved by adjusting the imager position or lens collar in the camera itself.
F-NUMHER
– The f –number indicates the brightness of the image formed by the lens, controlled by the iris. A smaller f-
number means a brighter image
F-STOP
– A term used to indicate the speed of the lens. The smaller the f-number, the greater is the amount of light
passing through the lens.
DEPTH OF FIELD
– The front to back zone in a field of view, which is in focus in the televised scene. With a greater
depth of field, more of the scene, near to far, is in focus. Increasing the f-stop number increases the depth of field of the
lens. Therefore, the lens aperture should be set at the highest f-stop number usable with the available lighting. In other
words, the depth of field is the area in front of the camera, which remains in focus. The larger the f- numbers the greater
the depth of field.
FIELD OF VIEW
– The maximum angle of view that can be seen through the lens of an optical assembly.
FOCAL LENGTH
– The distance from the centre of the lens to a plane at which point a sharp image of an object viewed
at an infinite distance from the camera is produced. The focal length determines the size of the image and the angle of the
view seen by the camera through the lens. That is the distance from the centre of the lens to the pick up device.
FORMAT
– Format is a term used to determine the size of the lens to be used with various types and sizes of imagers. A
1” format lens will work on 1”, 2/3”, ½” and, 1/3” format camera. A 2/3” format lens will work on 2/3’, ½” and 1/3” format
camera. A ½” format lens will work on ½” and 1/3” format camera. A 1/3” format lens will work on 1/3” format cameras
only. Using a smaller format lens on a larger format camera will cause distortions ranging from tunnel –vision to poor
back-focus capabilities.
LUX
– International system unit of illumination in which the meter is the unit of length. One lux equals one lumen per
square meter. 10 lux equals 1 foot-candle
Contact Pentax @ (905) 625-4930 www.pentaxcanada.ca
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