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Proceedings Paper

Telecentric large-field lenses using Fresnel optics
Author(s): Norbert Schuster; Thomas Schoenheit
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Paper Abstract

The practical application of Fresnel lenses in imaging systems is very much disputed. However, in large field, object side, telecentric lenses, conditions are such that the advantages of lightness, cheap production, and short construction length dominate the disadvantages. These disadvantages concern the reduced image quality. Starting from any paraxial relations, we present analytic equations which are useful in estimating the changes in the aberration balance, when a well compensated glass lens front group is replaced by a Fresnel lens singlet. The comparison of a pair of telecentric lenses with the same basic parameters, built with a glass lens front group and with a Fresnel singlet front group, confirms these equations. The reduced image quality, using a Fresnel singlet as front group in an object side telecentric lens, is caused by noncompensated lateral chromatic aberration, increased distortion values, higher stray light levels and reduced resolving power. For inspection purposes, the distortion is often not so important. If the work pieces are illuminated with monochromatic light, then chromatic aberrations become unimportant. Therefore, for machine vision inspection purposes, the object side telecentric ray path can be straightforwardly achieved using a Fresnel lens front group. This is an alternative to the well known, but expensive, glass front lens solutions.

Paper Details

Date Published: 11 February 2002
PDF: 9 pages
Proc. SPIE 4567, Machine Vision and Three-Dimensional Imaging Systems for Inspection and Metrology II, (11 February 2002); doi: 10.1117/12.455256
Show Author Affiliations
Norbert Schuster, Vision & Control GmbH (Germany)
Thomas Schoenheit, Vision & Control GmbH (Germany)

Published in SPIE Proceedings Vol. 4567:
Machine Vision and Three-Dimensional Imaging Systems for Inspection and Metrology II
Kevin G. Harding; John W. V. Miller, Editor(s)

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