Telecentricity

Telecentricity refers to a specific optical design characteristic where the principal rays of light entering the lens are parallel to the optical axis, or where the image rays exiting the lens are parallel to the optical axis. This parallel ray condition can be achieved in either the object space or the image space, or both.

In telecentric object space, the field of view remains constant regardless of the object's distance from the lens, within a certain range. This is because any changes in object distance do not alter the angle at which objects are viewed by the lens. This property makes telecentric lenses ideal for applications where precise dimensional measurements are critical, such as machine vision, metrology, and industrial inspection. By eliminating perspective distortion, telecentricity ensures that the apparent size of an object does not change with its position relative to the camera.

Conversely, telecentricity in image space means that the apparent size of the object is independent of its distance from the lens, as viewed from the image plane. This can be useful in certain projection systems. Lenses that are telecentric in both object and image space are often referred to as fully telecentric. The design of telecentric lenses typically involves complex arrangements of optical elements to achieve the required parallel ray paths.