Lense

What type of lens do you need?

Auto-Iris lenses work in the same way the human eye works, adjusting to different lighting conditions by dilating and constricting. Without Auto-Iris your image would be either too bright or too dark to be effective for surveillance. Generally if your camera is located outdoors, or indoors near windows that allow light conditions to change such as time of day or cloudy days, an Auto-Iris lens should be used.

Fixed-Iris If light conditions are constant a Fixed-Iris lens will be suitable.

Aperture

The measure of the light gathering capability of a lens. The maximum aperture is the minimum 'f' stop of a lens, generally the lower the 'f' stop the better.

Aperture Correction

Switchable correction circuit which electronically sharpens the image of a picture.

Focal Length

The focal length of a lens measured in millimetres, has a direct relationship to the angle of view that is obtained. A short focal length provides a wide angle of view and a large focal length provides a narrower angle of view.

C-Mount

Industry standard thread mouting portion on the rear of a lens. Note a C-mount lens can be used on a CS mount camera with a 5mm adaptor ring, however a CS-mount lens cannot be used on a C mount format camera.

CS Mount

Uses the same thread as C mount but requires the lens to be 5mm closer to the image sensor, new industry standard for lens mounting.

Lens Speed

Optical Speed is about how fast a lens collects lights and is defined by the f-number like f/1.2, f/2.0, etc. A fast lens would be rated f/8. The larger the f number, the slower the lens.

Lens Selection

 

Lens selection Guide for cameras with 1/3" Image sensor.

 

Lens Focal length (mm) Horizontal Angle-of -view

Distance from camera 
(1 meters)

Scene width in meters

Distance from camera 
(3 meters)

Scene width in meters

Distance from camera 
(5 meters)

Scene width in meters

Distance from camera 
(10 meters)

Scene width in meters

Distance from camera 
(15 meters)

Scene width in meters

2.5 105 1.92 5.76 9.6 19.2 28.8
3.6 72 1.33 4.0 6.67 13.33 20.0
4.0 62 1.2 3.6 6.0 12.0 18.0
6.0 45 0.8 2.4 4.0 8.0 12.0
8.0 34 0.6 1.8 3.0 6.0 9.0
12 23 0.4 1.2 2.0 4.0 6.0
16 17 0.3 0.9 1.5 3.0 4.5
25 11 0.192 0.576 0.96 1.92 2.88
39   0.123 0.369 0.615 1.23 1.846
51 5 0.094 0.282 0.470 0.941 1.412
69   0.069 0.208 0.348 0.695 1.043

 

Lux

"LUX" rating on cameras refers to its ability to function in low light conditions. The lower the rating - the lower the light conditions it can function under.


Vari-focal Lens

A camera lens in which the focus is not fixed, it can be manually or automatically adjusted.

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