The telecentric industrial lens is a lens specially designed to correct the parallax of the traditional industrial lens. In optics, telecentric meaning is a certain multi-element lens designs in which the chief rays are collimated and parallel to the optical axis in image and object space. Telecentric lens machine vision can be within a certain range of object distance so that the image magnification will not change with the change of object distance, which is a very important application when the measured object is not on the same surface.
The closer the target object of an ordinary industrial lens is to the lens (the shorter the working distance), the larger the image formed. When using an ordinary non-telecentric lens for size measurement, there will be the following problems:
(1) Because the measured object is not in the same measuring plane, the magnification is different;
(2) Large lens distortion;
(3) Parallax means that when the object distance increases, the magnification of the object also changes;
4) The resolution of the lens is not high;
5) The uncertainty of the position of the edge of the image due to the geometric characteristics of the visual light source.
The machine vision telecentric lens can effectively solve the above-mentioned problems of ordinary lenses, and there is no judgment error of this nature, so it can be used in high-precision measurement, metrology, etc. The telecentric lens machine vision is a high-end industrial lens, usually with superior image quality, especially suitable for size measurement applications.
No matter where, at the certain telecentric lens working distance, the same magnification will be obtained after refocusing, because the maximum field of view of the telecentric lens is directly related to the proximity of the lens diaphragm. The larger the lens size, the bigger the required scene. The telecentric measuring lens can provide superior image quality with less distortion than traditional fixed focus lenses. This telecentric lens design makes the image surface more symmetrical and can be used with software for precise measurement.
The advantages of ordinary lenses: low cost, practical, and versatile.
Disadvantages of ordinary lenses: the magnification will change and there will be parallax.
Ordinary lens application: imaging of large objects.
The advantages of a telecentric lens machine vision: the magnification is constant, does not change with the depth of field, and there is no parallax.
Disadvantages of telecentric lenses: high cost, large size, and heavy weight.
Application of telecentric lens: metrology, measurement based on CCD, microcrystals.
The focal length of the lens is divided into the focal length of the image side and the focal length of the object side. The image focal length is the distance from the main surface of the image to the focal point of the image. Similarly, the focal length of the object is the distance from the main surface of the object to the focal point of the object.
The image-side focal length is the distance from the intersection of the light rays passing through the lens to the lens when the incident light is parallel; when the point light source is a certain distance from the lens, the refracted light is parallel, and this distance is called the object focal length.