Telecentric optics for computational vision

Abstract

An optical approach to constant-magnification imaging is described. Magnification variations due to changes in focus setting pose problems for pertinent vision techniques, such as, depth from defocus. It is shown that magnification of a conventional lens can be made invariant to defocus by simply adding an aperture at an analytically derived location. The resulting optical configuration is called "telecentric." It is shown that most commercially available lenses can be turned into telecentric ones. The procedure for calculating the position of the additional aperture is outlined. The photometric and geometric properties of telecentric lenses are discussed in detail. Several experiments have been conducted to demonstrate the effectiveness of telecentricity.