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(1) Categorized by len installation mount
There are two common mounting styles for video camera lenses. C-mount lenses have a distance of 17.5 mm betweenthe flange of a lens and the CCD imaging sensor ( called flange-back distance ),The C- amount are suitable for both C-mount and CS-mount cameras. CS-mount lenses have a flange-back distance of 12.5 mm and require a 5 mm adapter for use with C-mount cameras. Both C and CS mount use the same thread pattern of 1.00/32mm.
(2 ) Categorized by CCD dimension
Camera lens depends on the CCD
dimension and should be used in harmony. When the CCD is
1/2”,1/3”,1/4” , the lens will also be1/2”,1/3”,1/4” accordingly.
( 3 ) Categorized by Iris
Manual Iris Lenses
The iris in a lens is what controls how much light is allowed through.
A manual iris lens allows you to adjust the iris manually. This is
usually done when the camera is installed. if there are drastic changes
in light levels, (eg sun shine), the picture could then be washed
out because the iris is letting
in too much light. These lenses are better suited for indoor
environment where lighting levels remainconstant.
Auto Iris Lenses
These lenses have an electronic circuit inside, which controls the
iris. The lens usually has a 4-pin connector which connects to the
camera, where it gets its power supply (9vDC) and its video signal. The
lenses electronics then analyses the video signal level and if there
are changes to light conditions, the iris then adjusts accordingly to
provide the best picture possible. Auto iris lenses are most suitable
for outdoor or entrance environment where light levels changes are
drastic.
There are two types of auto iris lenses:
Video Drive
With a video driven lens, the
video signal is picked up from the AI connector, which is connected to
the camera. Because the lensadjust the iris based on the video signal, the lens is referred to as a video drive lens.
DC Drive
DC driven lenses do not have the electronics for video processing, but rather only the motor that opens and closes the iris.
The whole processing process in
a DC driven lens is done by the cameras AI electronic section. A dc
drive opens and closes the irisbased on the DC voltage being provided by the camera. The DC drive lens relies on the camera to analyze the video signal.
Video drive lenses cannot be used with cameras that provide DC AI output, and DC drive lenses cannot be used with cameras that provide video AI output. They are not cross compatible!
( 4 ) Categorized by focal length/angle of view
Focal Length
Focal length is the distance from the optical center of the lens to the image sensor plane.
Angle of View
To put focal length in perspective, the focal length in the human eye is approximately 17 mm.
This focal length gives an
undistorted solid image angle of approximately 30 °. This is why an
angle of about 30 °. is considered astandard angle of view.
The focal length determines the
angle of view. The smaller the focal length, the bigger the angle of
view and thus the viewing area. Thebigger the focal length, the smaller the angle of view.
1 Fixed Focal Lenses
Fixed focal length lenses, as the name suggests, provide a fixed focal length, i.e. give one angle of view.
Normal " lens, Normal lens has an angle of view of 30 ° which is the same angle of view and perspective as seen by your eyes. A lens with
a focal length of 8mm on a 1/3" camera or a lens with a focal length of
12mm produces a field of view similar to the view producedby the human eye.
Wide Angle lens . Any lens shorter in forcal length (eg 4mm) than normal is referred to as "wide angle",
Wide angle lenses has an angle of view of at least 90° and can offer a wide field of view for broad image captures.
Telephoto lens. Any lens with longer focal length (eg16mm), is referred to as "telephoto". Telephoto Lenses has an angle of view of less than 20° narrow
Different lens’ focus length
2 Varifocal (Manual Zoom) Lenses
This lens lie between the
standard and wide angle lens. The varifocal lens enables the user to
change its focal length manually toproduce a zooming effect (narrowing the FOV)
3 Zoom or Motorized Lenses
Zoom or motorized lenses are
categorized into manual or motorized types. Manual type is only used in
research environment. In most of the surveillance environment,
motorized type lens will be used together. By remote controlling of the
focus and the angle of view, motorized lens can offer wide zooming
range, enabling the user to monitor wide zone and also able to zoom in
to look into details ofthe viewing object.
Typical lens offer the
flexibility for remote controlling of the focus and the angle of view.
This is critical for the supervision of high place,dangerous zone and . Typical lenses usually come in a range of 6x(8-48mm, F1.2), 8x(4.5-36mm), 10x(8-80mm), 12x(6-72mm), 20x(10-200mm). Besides, optical zoom, digital zoom can also be offered as option.
4 Pinhole Lenses
Pinhole lenses are small-diameter devices that are designed for insertion into tubes, holes, or other small areas.
Pinhole lenses with right-angle bends are called 90° pinholes.
5 Close Up Lenses
Close-up lenses provide short focusing distances for digital photography or imaging.
Field of view samples
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3.6 mm
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6mm
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Picture Area: 49' w x 35' h
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Picture Area: 29' w x 21'
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8mm
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15mm
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Picture
Area: 22' w x 16' h
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Picture Area: 12' w x 9' h
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55mm
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Picture Area: 3.25' w x 2.50' h
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（ 5 ）Optical Zoom / Digital Zoom
Optical zoom lenses physically
extend to magnify your subject. A motor controls the lens movement. The
greater the optical zoom, the more things can be taken far.
Digital
zoom crops your image and magnifies the result of the cropping. This
magnification process is called interpolation. To make the cropped area
bigger, digital zoom makes up, or interpolates, pixels to add to the
image, which may give less than satisfactory results.
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Original Picture
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10X Optical Zoom
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10X Digital Zoom
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