Telecentric lenses are a compound lens used in imaging systems to make objects appear to be the same size independent of their location in space.
It enables elimination of perspective or parallax error that makes closer objects appear to be larger than objects farther from the lens, thereby raising the quality of an image to a higher level than conventional lenses.
Telecentricity can be explained as a means to determine how the amount of magnification of an object within the field of view (FOV) changes with object distance.
The three main variations of these lenses are as follows:
- Entrance pupil at infinity, the telecentric lens is said to be object-space telecentric
- Exit pupil at infinity, the telecentric lens is said to be image-space telecentric
- Both pupils are at infinity, the telecentric lens is said to be double telecentric
Telecentric lenses are generally larger, heavier, and more expensive than the conventional lenses.
Telecentric lenses are required for most dimensional measurement imaging applications. In many machine-vision systems, precise and repeatable measurements need to be very consistent. These lenses provide extra precision to the machine-vision systems.
Telecentric lenses are capable of reducing and even totally eliminating the following problems, thereby becoming a vital part for developing high accuracy gauging applications:
- Perspective errors
- Image distortion
- Poor image resolution
- Magnification changes due to object displacement
- Object edge position uncertainty due to lighting geometry
Telecentric lenses are ideal for many other applications such as metrology, CCD based measurement, or microlithography.