Telecentric Lenses: A Unique Optical System Designed to Correct Parallax in Industrial Lenses

Telecentric lenses, specifically designed to correct the parallax of traditional industrial lenses, maintain a constant image magnification within a specific object distance range. This feature makes them perform excellently in complex scenarios where the measured objects are not on the same object plane. Additionally, their unique parallel optical path design has garnered favor in high-end visual application fields that have strict requirements for lens distortion.

Classification of Telecentric Lenses

Telecentric lenses, designed to correct the parallax of traditional industrial lenses, primarily aim to solve the issue of magnification differences caused by varying distances between the measured object or sensor and the lens. Based on their characteristics, telecentric lenses can be classified into the following categories:

Object-Side Telecentric Lenses

The design of object-side telecentric lenses is ingenious, with their aperture stop placed at the image-side focal plane of the optical system. This design ensures that the object-side principal rays converge with the optical axis at infinity on the image side. Even if the object distance changes, the image distance adjusts accordingly, but importantly, the image height always remains constant. This ensures that the size of the measured object is not affected. Such lenses play a critical role in industrial precision measurement and have minimal distortion, even achieving an ideal state of no distortion.

Image-Side Telecentric Lenses

Image-side telecentric lenses have a unique design, positioning their aperture stop at the object-side focal plane. Consequently, the image-side principal rays converge with the optical axis at infinity on the object side, forming a parallel center. The clever aspect of this design is that even if the sensor's installation position changes, the projected image size remains stable. These lenses are relatively less used in visual applications.

Bi-Telecentric Lenses

Bi-telecentric lenses combine the advantages of the aforementioned two types of telecentric lenses and play an important role in visual measurement and inspection. This innovative design, which integrates the benefits of both previous types, shows exceptional performance in the field of visual measurement and inspection.

Characteristics of Telecentric Lenses

Telecentric lenses, with their outstanding optical performance, play an indispensable role in precision optical measurement systems. They boast high resolution, extremely low distortion, no perspective error, telecentric design, and ultra-wide depth of field. These features effectively overcome issues found in ordinary optical lenses, such as image distortion, angle error, and light source interference, thereby significantly improving measurement accuracy.

Comparison with Ordinary Lenses

Ordinary industrial lenses have the characteristic that the closer the target object is to the lens, the larger the formed image. However, using ordinary lenses for size measurement faces a series of challenges:

Ordinary industrial lenses are cost-effective, highly practical, and widely applicable, but they face several issues during size measurement. First, the measured objects may not be on the same measurement plane, leading to magnification differences. Secondly, lens distortion is a noteworthy problem. Moreover, when the object distance changes, parallax occurs, affecting the accurate measurement of the object. Additionally, the relatively low resolution of ordinary lenses limits their measurement precision. Lastly, the geometric characteristics of visual light sources create uncertainty at the image edges, which needs to be addressed.

In contrast, telecentric lenses excel in high-precision measurement and metrology. They offer constant magnification, are unaffected by changes in depth of field, and have no parallax, effectively solving the problems associated with ordinary lenses. Despite the higher cost, larger size, and heavier weight of telecentric lenses, their excellent image quality and suitability for size measurement make them an ideal choice in high-end industrial fields.