Camera Specifications Play A Big Role in The Performance of IR Illuminator

- Dec 28, 2015-

Relation between IR illuminator and camera lens
The reasons for the importance of camera lens in relation to the IR illuminator include the following:

i. Luminous flux of lens (lumen)

ii. Angle of the lens and IR illuminator

iii. Dimension of the camera chipset

Solution

1. Luminous flux of the lens – to choose the lens with the least F-ratio that has the biggest luminous flux.
2. How to choose the angle of what the appropriate focus is, according to the diagram, to work well with the infrared illuminator.

a. If working with a fixed lens
  
i. Measure the distance between the IR camera and object.
   ii. Select the lens with appropriate focus according to the diagram.
   iii. Double check the angle of the lens.
   iv. Choose the IR illuminator which can cover the entire range. 

b. If working with a zoom lens 
   i. Measure the nearest and farthest point of measurand from the camera.
   ii. Selective focus of the lens.
   iii. Double check the angle range of the lens.
   iv. Choose the IR illuminator which can cover the entire range. 

3. Calculating the formula for focus of the lens, to display the ratio of the measurand, how to select the focus of lens for a 1/3” chipset or larger.
a. Focus of lens for 1/3” chipset:

       i.  F = 4.8 x L/W
       ii.  F = 3.6 x L/H
b. Focus of the lens for 1/2” chipset:
       i.  F = 6.4 x L/W
       ii.  F = 4.8 x L/H

For example: 15m away from the camera there is a man, 1.7 m tall, which occupies 1/4 height on the screen. F= 3.6 x 15m/1.7m x 1/4 = 8 mm; where F = Focus, L = Distance between lens and measurand; H = height of the measurand; W = weight of measurand.

    The calculating formula is based on the measurand range filling the entire screen.  If it fills only 1/4 of the screen, multiply the focus by 1/4.

    Depending upon a reasonable price and cost, the angle range of one IR illuminator may not cover the expected range of the zoom camera. The edge of the screen will be gloomy or fuzzy. The solution is to combine several IR illuminators with small angles together or using IR Illuminators with different illuminating distances together with technical expertise.

Selection of camera
The camera should have day and night, color and black-and-white functions, or IR function, and should be sensitive to 850nm IR light. The dimension of the chipset should be up to 1/3 inch and below 0.01 Lux. If using a regular color camera, the IR filter should be replaced with one that is penetrable to 850nm IR light. If you only remove the IR filter without replacing it, metachromatism will occur.

Compare to the spectrum chart of camera , when the relative response for 850nm wavelength of camera is 0.5lux above, the induction infrared effect is better, thus IR illuminator can achieve effective distance farther.

The minimum intensity of illumination, also known as the sensitivity, which is the CCD light sensitivity to the environment, or the minimum light needed for CCD image formation(Unit is LUX). The smaller the value, the less the light needed, cameras are more sensitive. The level of moonlight and starlight camera means such intensifying camera can work in a very dark condition.

Matters that need attention

  1. Adjustment of the Auto Iris Lens.  The auto iris lens has DC and video drive modes. Adjust the ALC (automatic level control) to fit the IR illuminator exactly; otherwise the illuminative distance will be markedly affected.

  2. The deviation angle of the mounting should be accurate within 2° (in relation to the plane of the camera).

  3. Operating temperature should be between -20° C and 50° C.

  4. Optimum Distance. Halfway between the illuminate distance and the IR illuminator is the optimum distance. (Test by 1/3 CCD, 0.01 Lux camera).

  5. Voltage. Use according to the voltage rating of every product.

  6. Debugging. IR illuminators need to debug before they are used, which, in relation to the camera and other equipment, may need technical assistance from a qualified technician.

Relation table of technical requirements between the camera and IR Illuminator

Optimum distance is relation to the focus and angle of the camera lens, based on a person (1.7m tall) occupying 1/4 height on the screen.

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