The Advantages of Telecentricity

To be able to perform repeatable quickly, high exactitude measurements is quite critical to aggrandize the performance of many automation vision systems. For these kind of systems, a telecentric lens grants the highest possible verity to be obtained. Here we will discusses the solitary performance characteristics of Telecentric Lenses and how telecentricity can jounce a system’s performance.

What is Zero Angular Field of View and the Elimination of Parallax Error?

Conventional lenses have an angular field of view in such a way that as the distance between the object and lens cumulates, the magnification shrinks. This is exactly how the human vision behaves, and dispenses to our depth sagacity. This angular field of view consequences in parallax, also known as perspective error, which downturns exactitude, as the inspected measurement of the vision system will change if the object is displaced (even when remaining within the depth of field) due to the magnification tempering. Telecentric Lenses dispose of the parallax error characteristic of standard lenses by having a constant, non-angular field of view; at any outpost from the lens, a Telecentric Lens will always have the same field of view. See figure below to understand the difference between a non-telecentric and a telecentric field of view.

Telecentric Lens

Figure 1: Field of View comparison of a Conventional and Telecentric Lens. Note the conventional lens’s angular field of view and the Telecentric Lens’s zero angle field of view.

A Telecentric Lenses’ invariable field of view has both benefits and suppression for gauging applications. The primary advantage of a Telecentric Lens is that its magnification does not modify in respect to depth. The figure below shows two different objects at different working stretches, both imaged by a Fixed Focal Length (non-telecentric) Lens (center) and a Telecentric Lens (right). Take a note that in the image taken with a Telecentric Lens, it is almost impossible to say which object is anterior of the other while with the Fixed Focal Length Lens, it is quite evident that the object that emerges smaller is located farther from the lens.


Figure 2: The Angular Field of View of the Fixed Focal Length Lens decodes to Parallax Error in the Image and makes the two Cubes emerge to be of contrasting sizes.

While the above figure is radical in terms of a dynamic distance shift, it delineates the importance of minimizing parallax error. Several automated investigation tasks are imaging objects that run through the field of view of an imaging system, and the location of parts is seldom perfectly repeatable. If the working distance is not indistinguishable for each object that the lens is imaging, the measurement of each object will dissent due to the magnification shift. A machine vision system that yields different results based on a magnification calibration error (which is compulsory with a Fixed Focal Length Lens) is a vulnerable solution and cannot be used when high fidelity is compulsory. Telecentric Lenses remove the concern about measurement errors that would else occur due to factors such as a vibrating conveyor or vague part positions.

Article is posted by Optics For Hire – lens design and manufacturing Consultant.

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