Telecentric Lenses vs. Conventional Lenses

Ordinary, conventional lenses have angular fields of view. As the distance between one of these conventional lenses and the object increase, the magnification will decrease. This angular field of view also causes perspective error (parallax).

Telecentric lenses feature a constant field of view that is non angular: the field of view does not depend on the distance. This means magnification doesn’t change based on depth. It turns out this is extremely helpful for machine vision applications: often, the positioning of parts varies between objects, and using a telecentric lens allows us to get consistent imaging even when a conventional lens would give us calibration errors.

While telecentric lenses don’t have a larger depth of field, inherently, any blurring that happens is symmetrical over both sides of the focal point. This means that features of interest (corners, say) will maintain their center of mass location and can be measured accurately even if they are not completely in focus.

Telecentric lenses also have lower distortion values than your conventional lens. This makes the distortion-eliminating calibrations we often perform as a matter of course unnecessary, leading to a much lower CPU load in measurement software. Long working distance is a key advantage of telecentric lenses, allowing them to maintain accurate measurements even when the object is placed far from the lens. This feature is particularly beneficial in industrial applications where large objects or components need to be inspected. Large image size capability in telecentric lenses ensures that even large objects can be captured in a single frame without losing accuracy. This is essential for applications requiring the inspection or measurement of sizable items. Image side telecentric lenses ensure that the exit pupil is at infinity, which means that the chief rays are parallel to the optical axis in the image space. This is crucial for dimensioning systems where measurement accuracy must be maintained regardless of the image sensor’s distance within the depth of focus.