A
ABBERATION - Any inherent deficiency of a lens or optical system
which is responsible for imperfections in shape or sharpness of the image.
Automatic Gain Control (AGC) - 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 potentiometer
is turned towards PEAK, and decreased when turned towards AVERAGE.
ANGLE OF VIEW - May be expressed in Diagonal, Horizontal or, Vertical.
Smaller focal lengths give a wider angle of view.
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 an F-number.
The international aperture scale is: F1, F1.4, F2, F2.8, F4, F4.6, F8,
F11, F16, etc.
ASPHERICAL LENS - A lens which one or more of the elements have
a non-spherical surface. Aspherical surfaces are shaped to reduce the
spherical and other aberrations.
AUTO-IRIS LENS - A lens with an electronically controlled iris.
This allows the lens to maintain one light level throughout varying light
conditions.
B
BACK FOCUS - Back focus is a term used to describe the relationship
of the distance of the lens to the image device. This distance is critical
to maintain the proper depth of field through changing focal lengths and
varying light conditions. The correct back focus is normally achieved
by adjusting the image pick-up device on the camera itself.
Back Light Compensation (BLC) - 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.
C
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", ½", 1/3" and, ¼"
C-MOUNT - An industry standard for mounting a lens to a camera
where a 1' x 32 thread is employed and the distance from the image plane
is 17.52mm from the shoulder of the lens. A C-mount lens may be used CS-mount
camera with the use of a 5mm-adapter ring.
CS-MOUNT - A relatively new industry standard for mounting a lens
to a camera where a 1" X 32 thread is employed and the distance from
the image plane from the shoulder of the lens is 12.52mm. A CS-mount lens
may NOT be used on a C-mount camera.
D
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.
E
EXTENSION TUBES - Various size spacers used between the camera
and lens to reduce the Minimum Object Distance. Not recommended for use
with zoom lenses due to the loss of tracking ability.
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.
F-STOP - A term used to indicate the speed of a lens. The smaller
the F-number the greater amount of light passes through the lens.
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.
G
H
HUNTING - An industry term used to describe an auto-iris lenses
inability to stabilize under certain light conditions.
I
IRIS - A mechanical diaphragm which can be controlled manually
or automatically to adjust the lens aperture.
J
K
L
LENS FORMAT - The approximate size of a lens' projected image.
In most cases the lens will project an 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
that has 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.
LENS SPEED - Refers to the lens aperture or its ability to transmit
light. This is measured in F-stops.
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.
M
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.
MINIMUM OBJECT DISTANCE (MOD) - The closest distance a given lens
will be able to focus upon an object. Generally the smaller the focal
length the shorter the MOD. This distance can be altered with use of extension
tubes.
N
O
P
PINHOLE LENS - Lenses used primarily in covert applications where
the camera/lens must remain out of sight.
PRE-POSITION LENSES - Pre-position lenses are specially designed
lenses with extra mechanical/electrical components to allow for computer
interfacing. This function allows the lens (when used with the appropriate
controller) to provide feedback to the controller with information relevant
to zoom and focus positioning allowing the controller to quickly scan
to a pre-selected scene, arriving in focus at the proper zoom point without
operator intervention.
Q
R
S
SPOT FILTER - A neutral density filter paced at the center of
one of the elements (or on an iris blade) to increase the high end of
the F-stop range of the lens.
T
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.
TRACKING - A zoom lenses ability to remain in focus throughout
the entire zoom range.
U
V
VARI-FOCAL - A low cost version of a zoom lens designed to provide
versatility. This lens does not have the ability to track from wide to
telephoto.
VIDEO TYPE LENS - An auto-iris lens with internal circuitry for
processing of the video signal which controls the iris movements.
W
X
Y
Z
ZOOM LENS - A lens with the ability to change its focal length
manually or through the use of a controller to cover a variety of needs.
ZOOM RATIO - The ratio of the starting focal length (wide) to
the ending focal length (telephoto) of a zoom lens. A 10X zoom will magnify
the image at the wide end by 10 times. Examples of a 10X zoom lenses;
8mm~80mm, 12mm~120mm.