If the machine vision system cannot collect clear and accurate images, it cannot guarantee whether the subsequent series of operations are correct or meaningful. Therefore, in the entire machine vision system, image collection is a crucial link.
The machine vision lens is an important component to realize the measurement and judgment of the machine vision system using the machine instead of the human eye. The quality of the lens directly affects whether the entire system can obtain high-quality images and whether it can achieve automation and intelligence.
Next, we will have a certain understanding of the machine vision lens by explaining and analyzing the main parameters of the optical lens.
The focal length is the distance from the center point of the lens to the focal point where a clear image is displayed. The focal length is an important performance indicator of a machine vision lens, and its length determines the size of the image, the size of the angle of view, and the size of the depth of field. The shorter the focal length, the larger the angle of view, and the larger the range that can be observed; conversely, the longer the focal length, the smaller the angle of view, and the smaller the range that can be observed. In order to better realize the acquisition of images, the lens is divided into two categories: fixed focus and zoom.
The aperture is a mechanical device that changes the size of the middle hole in the lens, and its size is determined by the ratio of the focal length to the transmit aperture. The smaller the ratio, the larger the aperture, the greater the amount of light transmitted per unit time; conversely, the larger the ratio, the smaller the aperture, and the smaller the amount of light transmitted.
There is a certain limit to the clear range of the object to be photographed by the machine vision lens, and the depth of field refers to the range that can be clearly displayed within a certain distance in front of and behind the object after the object is clearly focused. Depth of field is closely related to aperture, focal length, and shooting distance:
(1) The larger the aperture, the smaller the depth of field; the smaller the aperture, the larger the depth of field;
(2) The longer the focal length, the smaller the depth of field; the shorter the focal length, the greater the depth of field;
(3) The farther the shooting distance, the greater the depth of field; the closer the distance, the smaller the depth of field.
As the name suggests, the distance from the working surface of the lens to the object to be measured is the so-called shooting distance.
In addition to the above four main parameters that affect each other, the parameters of the machine vision lens also include the size of the CCD, the interface with the camera, the resolution, the field of view, the optical magnification and so on. It is these parameters that affect whether the machine vision lens can play its role. When selecting a lens, it must be based on the principle of being suitable for detection needs. Therefore, it is essential to understand its parameters.