6Basic parameters and 3selection principles of machine vision lens
- Basic parameters of machine vision lens
The main parameters of a lens are focal length, resolution, working distance, depth of field, the field of view, distortion, and so on.
- Resolution: the number of black-and-white fringes that the lens can resolve in-unit millimeters at the image plane, which is affected by the lens structure, material, processing accuracy, and other factors. The resolution of the lens and camera affects the quality of the final image.
- Working distance: generally refers to the distance from the front of the lens to the object under test, less than the minimum working distance, greater than the maximum working distance of the system generally can not clearly image.
- Depth of field: focusing on the working distance of the best focus of the lens, there is a range in front and back, in which the lens can image. Depth of field is affected by focal length and aperture: the shorter the focal length of the lens, the greater the range of depth of field, and the smaller the aperture, the greater the depth of field.
- Field of view: the area covered by an image acquisition device, that is, the size of the object plane corresponding to the image on the target surface.
- Focal length: the focal length of a lens is slightly different from that of a convex lens because the lens is a combination of convex lenses. Focal length is the distance from the center of the lens to the sharp image formed on theplastic plane. The focal length can be adjusted and can be divided into fixed-focus lenses and zoom lens two categories.
- Distortion: image distortion caused by the inherent characteristics of a convex lens, which can not be eliminated. Aberrations only affect the geometry of the image, but not the clarity of the image.
- Selection principle
In the machine vision system, the main function of the lens is to place the image target on the light-sensitive surface of the image sensor. The quality of the lens directly affects the overall performance of the machine vision system. The reasonable selection and installation of the lens is an important link in the design of the machine vision system.
- The commonly used lens interface types are C port, CS port, F port, etc. When selecting a lens, we should first determine the interface type of the lens.
The focal length is one of the most important parameters of the camera. According to the overall size of the system and the working distance, the focal length of the lens can be calculated by combining the ratio of the target size and the range to be measured.
- The target size of the lens should be larger than that of the camera, otherwise, the amount of light input may lead to the loss of image information.
- Considering the resolution, distortion, and depth of field, the aperture is determined according to the illumination environment.
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