How to set up industrial cameras to their best condition

Industrial cameras are equivalent to the lens of the human eye. Without the lens, the human eye cannot see any objects; without the lens, the image output by the camera is a vast expanse of white without clear image output. This is consistent with the principles of our home cameras and cameras. When the muscles of the human eye cannot stretch the lens to the normal position, which is often referred to as myopia, the scene in front of you becomes blurry. The cooperation between the camera and the lens also has a similar phenomenon. When the image becomes unclear, you can adjust the back focus of the camera and change the distance between the CCD chip and the industrial lens reference plane (equivalent to adjusting the position of the human eye lens) to make the blurred image clear.

It can be seen that the role of lenses in closed-circuit surveillance systems is very important. Engineering designers and construction personnel have to deal with lenses frequently: designers need to calculate the focal length of the lens based on the object distance and imaging size, and construction personnel often conduct on-site debugging, part of which is to adjust the lens to its optimal state.

All camera lenses are threaded. There are two industrial standards for CCD camera lens installation, namely C mount and CS mount. The threads are the same, but the distance from the lens to the photosensitive surface is different.

According to the camera lens size, the lens can be divided into specifications such as 1 inch, 2/3 inch, 1/2 inch, 1/3 inch, 1/4 inch, 1/5 inch, etc. The following is a simple chip size specification table:

If the lens size is larger than the camera CCD target surface size, the image field of view will be smaller than the lens field of view, that is, the field of view of the lens cannot be well utilized; if the lens size is smaller than the camera CCD target surface size, the "tunnel effect" will occur, that is, the image will have a circular black frame, like being shot in a tunnel. Surveillance cameras are generally smaller, even less than 1/3 inch; industrial cameras are slightly larger, generally ranging from 1/2 inch to 1 inch; the traditional 135 camera film is larger than the current general photosensitive chip, 36mm * 24mm (1.4 inch * 0.9 inches), the diagonal length of the screen is 43mm (1.7 inches), that is, a 1.7-inch, 120 medium format camera has three photosensitive surface sizes: 45*60mm, 60*60mm and 90*60mm, which means the frame is larger.

The main function of the aperture is to control the amount of light from the lens to meet the appropriate illumination required for imaging. The larger the aperture, the greater the target imaging illumination, the greater the camera output signal strength, and the higher the signal-to-noise ratio.

It can be understood that the larger the clear aperture, the greater the amount of light that passes through; but what we care about is the amount of light reaching the chip, and the longer the focal length, which means that the chip is farther from the center of the lens, and the corresponding light is weaker. Therefore, the parameters of the standard aperture size should be related to two variables, aperture and focal length.

The aperture coefficient, or F number, is a parameter used to characterize the size of the aperture. It is equal to the ratio of the lens focal length f and the clear aperture D. The luminous flux is inversely proportional to the square of the F value. The smaller the F value, the greater the luminous flux. The rule of F value is that the latter value is exactly √2 times of the previous value. Therefore, when the aperture is increased by one stop, the amount of light is reduced by 2 times.

Commonly used values ​​are:

• 1.4
• 2
• 2.8
• 4
• 5.6
• 8
• 11
• 16
• 22

Generally, the aperture can be adjusted, and there are manual iris (manual iris) and automatic iris (autoiris).

The manual aperture industrial lens is the simplest industrial lens and is suitable for use under relatively stable lighting conditions. The manual aperture is composed of several metal sheets. The luminous flux is adjusted by a ring on the outer diameter of the lens. Turn this circle to make the aperture smaller or larger. In environments with large changes in lighting conditions or when it is not used to monitor a fixed target, an automatic aperture industrial lens should be used. For example, outdoors or in places where artificial lighting is frequently switched on and off, the aperture movement of the automatic aperture lens is driven by a motor, and the motor is controlled by the video signal of the camera.

There are two types of automatic aperture industrial lenses:

• One is to transmit a video signal and power from the camera to the lens to control the aperture on the lens. The lens itself contains an amplifier circuit to convert the video amplitude signal from the camera into the control of the aperture motor, which is called video (VIDEO) drive type;

• The other type uses the DC voltage on the camera to directly control the aperture, which is called DC (DC) drive type. This type of lens only contains a galvanometer aperture motor and requires an amplifier circuit in the camera.

For various types of automatic aperture industrial lenses, there are usually two adjustable knobs. One is ALC adjustment (metering adjustment), which has two options: peak metering and average metering according to the target lighting conditions. Generally, the average metering level is used; the other is LEVEL adjustment (sensitivity), which can make the output image brighter or darker.