The telecentric lens types are mainly divided into object space telecentric lens, image space telecentric lens and bi-telecentric lens.
1. Object space telecentric lens
The object space telecentric lens places the aperture diaphragm on the image space focal plane of the optical system. When the aperture diaphragm is placed on the image-side focal plane, even if the object distance changes, the image distance also changes, but the image height does not change. There is no change, that is, the measured object size will not change. Object space telecentric lenses are used for industrial precision measurement, with minimal distortion, and high performance can achieve no distortion.
2. Image space telecentric lens
The image space telecentric lens, by placing an aperture stop on the object focal plane, makes the chief ray of the image side parallel to the optical axis, so that although the installation position of the CCD chip is changed, the projected image size on the CCD chip remains unchanged.
3. Bi-telecentric lens
The bi-telecentric lens combines the advantages of the above two telecentric lenses. In industrial image processing, generally only object space telecentric lenses are used. Sometimes there are telecentric lenses on both sides (of course the price is higher). In the field of industrial image processing/machine vision, the image space telecentric lens generally does not work, so this industry basically does not use it.