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Design Principle and Technical Advantages of Telecentric Lens

Ⅰ. Telecentric lens design

The purpose of telecentric lens design is to eliminate the difference in magnification caused by the inconsistency of the distance between the measured object and the lens. According to the classification and design principles of telecentric lenses:

1. The design principle of the object space telecentric light path

The convergent center of the object space chief ray parallel to the optical axis is located infinitely far away from the image space, which is called the object space telecentric light path. Its function is: it can eliminate the reading error caused by inaccurate focusing of the object.

2. The design principle of the image-side telecentric light path

The convergent center of the chief ray of the image side parallel to the optical axis is located infinitely far away from the object, which is called the image-side telecentric light path. Its function is to eliminate the measurement error caused by the inaccurate focusing on the image side.

3. The design principle of the telecentric optical path on both sides

It integrates the dual functions of object space/image space telecentricity, and is mainly used in the field of vision measurement and detection. Bi-telecentric lens adopts this principle.

Ⅱ. Technical advantages of telecentric lens

1. High resolution

The image resolution is generally measured by the CTF (contrast transfer function) that quantifies the existing spatial frequency contrast of the image sensor, and the unit is lp/mm. Most machine vision integrators often just gather a large number of cheap low-pixel, low-resolution lenses, and finally can only generate blurred images. With a telecentric lens, even with a small pixel image sensor, high-resolution images can be generated.

2. True telecentric lens design: ultra-wide depth of field and low distortion

There was a view that the telecentric lens mainly solves the distortion problem. In fact, the telecentric lens solves not only the distortion problem, but the low distortion is only an additional attribute of the telecentric lens. The unique optical characteristics of the telecentric lens: when the object moves in the field of view, its magnification in different positions will not change, which determines that it cannot be replaced by ordinary industrial lenses in some fields. For example, its larger depth of field can be well adapted to the working environment on site, which is not a problem that can be solved only by algorithms.

3. Unique parallel light path design

Designing a telecentric lens for parallel-light imaging is not complicated in theory, but it is another matter to achieve a certain resolution and imaging quality. The design and manufacture of a telecentric lens is indeed more difficult than a lens in the general sense. The reason is that the size of the optical lens of the telecentric lens is relatively large, which makes the correction of various phase differences of the edge light more difficult.

In order to obtain a good image quality of the edge field of view, higher product design and manufacturing accuracy is required, and in many cases it is necessary for the designer to have relatively rich design experience.