Telecentric lenses are mainly designed to correct the parallax of traditional industrial lenses. Within a certain range of object distance, the magnification of the obtained image will not change. This is very important for the application of objects that are not on the same plane. Telecentric lens has been favored by machine vision applications that have high requirements for lens distortion due to its unique parallel optical path design. The purpose of telecentric lens design is to eliminate the inconsistent magnification caused by the different distances between the measured object (or CCD chip) and the lens. Based on its unique optical characteristics, such as high resolution, ultra-wide depth of field, ultra-low distortion, and unique parallel light design, telecentric lens brings a qualitative leap to the precision inspection of machine vision.
The closer the object is to the ordinary industrial lens (the shorter the working distance), the larger the resulting image will be. When using an ordinary lens for size measurement, the following issues may arise. The different magnifications caused by the object being measured not being on the same measurement plane; large lens distortion; parallax, that is, the magnification of the object changes when the object distance increases; low lens resolution; the uncertainty of the image edge position caused by the geometric characteristics of the visual light source.
Telecentric lenses can effectively solve the above problems of ordinary lenses and there is no judging error of this property, so it can be used in high-precision measurement, metrology, and other fields. Telecentric lens is a high-end industrial lens with outstanding image quality, especially suitable for size measurement applications. No matter where it is, at a specific working distance, after refocusing, it will have the same magnification because the large field of view range of the telecentric lens is directly related to the proximity of the lens aperture, and the larger the lens size, the larger the required field. The telecentric measuring lens can provide image resolution, and its distortion is smaller than that of traditional fixed-focus lenses. This optical design makes the image surface more symmetrical and can be used with software for precision measurement.
The advantages of ordinary lenses are low cost, practicality, and versatility. The disadvantages are that the magnification will change and there is parallax. Ordinary lenses are applied to imaging large objects. The advantages of telecentric lenses are constant magnification, not changing with the depth of field, and no parallax. The disadvantages are high cost, large size, and heavy weight. Telecentric lenses are applied to metrology, CCD-based measurement, and microcrystallography.