21 Jun 2011 Telecentric lens have constant magnification when changing in objective distance. There is no perspective error when viewing 3D object. It is widely used in machine vision and high precision optical measurement. There are three types of telecentric lens: (1) objective side telecentric (2) image side telecentric and (3) dual side telecentric
Object Telecentric Lens
when the aperture stop is positioned to let the exit pupil lies in the back focal plane, the entrance pupil will be at infinity, and the chief rays through the centre of the exit pupil will be parallel to the axis in the object space. The magnification remains constant when the objective distance varies within a specific range. This specific range is call telecentric depth.
Image side Telecentric
when the aperture stop is positioned to let the entrance pupil in the front focal plane, the exit pupil is at infinity, and the chief rays through the centre of the entrance pupil from all points on the object are parallel to the axis in the image space.
Dual Telecentric Lens
It combines the advantages of both object and image side telecentric lenses. In dual side telecentric lens both the entrance pupil and exit pupil are at infinity, and only the chief rays are parallel to axis in both object and image space.
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