Basic Parameters And Selection Of Optical Lenses

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An optical lens is a key component in a machine vision system. Its basic function is to transform an optical signal into an ordered electrical signal. Choosing the right optical lens is also an important part of the design of the machine vision system. The optical lens not only directly determines the image resolution and image quality, but also directly relates to the operating mode of the whole system.
Optical lens performance advantages
A good optical lens should have high precision, high definition, good color reproduction, low noise, etc., and can be programmed to control the exposure time, brightness, gain and other parameters through the computer, and the image window is steplessly scaled with an external trigger input. Features such as flash control output. Microvision, a well-known optical lens manufacturer and seller in China, combines years of R&D and production experience with customer needs, and carefully selects the precautions and necessary parameters when selecting optical lenses, so that general customers can make reasonable choices.
Basic parameters of optical lens
Resolution
The number of pixels of the image captured by the camera each time generally corresponds to the number of pixels arranged on the surface of the photosensor, such as 1920*1080.
Pixel depth
The number of bits per pixel data is usually 8bit, 10bit, 12bit. The resolution and pixel depth together determine the size of the image. For example, for a 5 megapixel pixel with a pixel depth of 8 bits, the entire image should have 5 million*8/1024/1024=37M (1024bit=1KB, 1024KB=1M). Increasing the pixel depth enhances the accuracy of the measurement, but it also reduces the speed of the system and increases the difficulty of system integration (increased cable, larger size, etc.).
Large frame rate/line frequency
The speed at which the camera captures and transmits images is typically the number of frames captured per second (Frames/Sec) for area array cameras and the number of lines (HZ) collected per second for line array cameras.
Exposure method and shutter speed
Industrial line array cameras are progressive exposure mode. You can choose the fixed line frequency and external trigger synchronization mode. The exposure time can be consistent with the line period, or you can set a fixed time. The area array camera has frame exposure and field exposure. And several common ways of rolling exposure, industrial digital cameras generally provide the function of external trigger capture, the shutter speed is generally up to 10ms, and the high speed camera will be faster.
Cell size
The cell size and the number of pixels (resolution) together determine the size of the camera's target surface. At present, the industrial digital camera pixel size is generally 3μm~10μm. Generally, the smaller the pixel size is, the more difficult it is to manufacture, and the less the image quality is improved.
Spectral response characteristics
It refers to the sensitivity of the pixel sensor to different light waves. The general response range is 350nm~1000nm. Some cameras add a filter in front of the target to filter out the infrared. If the system needs to be sensitive to infrared, the filter can be removed.
Optical lens noise
Noise refers to signals outside the actual imaging target that are not desired to be acquired during imaging. Generally divided into two categories, one is the shot noise caused by the effective signal, this kind of noise exists for any camera; the other is the inherent noise of the camera itself and the signal without light. It is due to the inherent noise caused by the image sensor readout circuit, camera signal processing and amplification circuit, and the inherent noise of each camera is different.
Signal to noise ratio
The signal-to-noise ratio of the camera is defined as the ratio of signal to noise in the image (the ratio of the average gray value of the effective signal to the root mean square of the noise), which represents the quality of the image. The higher the image signal-to-noise ratio, the better the camera performance and image quality. .