Telecentric lens

Telecentric lenses are special optical lenses, which are characterized in that the entrance or exit pupil is located at infinity. A distinction is made between the object side, the image side, and both sides telecentrics.

Telecentric lenses are used mainly in microscopes and measuring technology, such as optical micrometers. But you will also be projected in systems such as profile projectors or photolithography equipment application. Show the main beams linearly scaled inward is of Perizentrie when they scaled linearly outward show is spoken by Entozentrie. Most normal lenses are approximately entozentrisch. Optimal entocentric lenses are distortion-free as a wide angle lens in use, pericentric find their application in concurrent object inspection (eg cans ) from several sides.

Object -side telecentrics

An object-side telecentric beam path is used to detect objects without perspective distortion. The entrance pupil is located at infinity, so that the main beam in the object space all run parallel to the optical axis. Therefore, the front lens needs to be at least as large as the object to be imaged.

Another feature of this optical path is that the magnification in the axial object displacement does not change. The image appears therefore independent of object distance is always the same size. But it is out of focus when the object is outside of the ideal object level. This property is utilized in measuring lenses to allow a certain position tolerance of the specimen. The tolerable distance range is determined by the depth of field and is specified in the data sheets. In microscopes of constant image scale allows for easy focusing.

On the object side telecentric beam path is most easily realized by a single converging lens with an aperture in the image-side focal plane.

Image side telecentrics

An image side telecentric beam path is mainly used for parallelization of the ray path. It is used inter alia in digital camera lenses to prevent pixel vignetting., The exit pupil is located at infinity, so that the beams all meet cone perpendicular to the image plane. The simplest structure of this consists of a single focusing lens having an aperture stop in the object-side focal plane.

Bilateral telecentrics

A double telecentric beam path is the combination of object-side and image side telecentric beam path. These lenses can be found especially in measurement technology, but also in photolithographic manufacturing process applications. Entrance and exit pupil are in the infinity, so the system is afocal.

In contrast to pure object-side telecentrics the tolerable object position is not limited here by the depth of field. You can refocus the image plane without changing the magnification. The simplest structure to consist of two converging lenses, between which an aperture is attached. The distance of a lens to the aperture of the respective focal length must correspond.

A double telecentric lens has theoretically no geometric aberrations such as distortion.