Telecentric lens VS normal lens
The telecentric lens is a lens specially designed to correct the parallax of the traditional lens. It can be within a certain object distance range, so that the image magnification will not change with the change of the object distance. This pair of objects is not available. The situation on the same surface is a very important application.
There are three main categories of telecentric lenses:
1. Object-side telecentric lens
The object-side telecentric lens places the aperture diaphragm on the image-side 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. The object-side telecentric lens is used for industrial precision measurement, with minimal distortion, and high performance can achieve no distortion.
2. Image side telecentric lens
The image side 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.
The advantage of the image-side telecentric lens is to make the camera chip get uniform light, because only the light parallel to the optical axis can be incident on the micro lens in front of the CCD/CMOS chip, so that the image will not appear shadows.
3. Telecentric lens on both sides
This lens combines the advantages of the above two lenses. In industrial image processing/machine vision, generally only object-side 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, image-side telecentric lenses generally do not work, so this industry basically does not use it.
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 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, that is, when the object distance becomes larger, the magnification of the object also changes;
4. The resolution of the lens is not high;
5. The uncertainty of the edge position of the image due to the geometric characteristics of the visual light source.
Telecentric lenses advantages
The telecentric lens can effectively solve the above-mentioned problems of ordinary lenses, and there is no interpretation error of this nature, so it can be used in high-precision measurement, metrology and other aspects. Telecentric lens is a high-end machine vision lens, usually with superior image quality, especially suitable for size measurement applications.
No matter where, at a specific working distance, the magnification will be the same after refocusing, because the maximum field of view of a telecentric lens is directly related to the proximity of the lens diaphragm. The larger the lens size, the required field of view is Bigger. The telecentric measurement lens can provide superior image quality with less distortion than traditional fixed focus lenses. This optical design makes the image surface more symmetrical and can be used with software for precise measurement.