<title>Telecentric large-field lenses using Fresnel optics</title>

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 oftelecentric 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. Ifthe 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.

Design of off-axis reflective projection lens using spherical Fresnel surface

“…. (1) where c is the curvature of the reflective surface, k is conic constant, a 2 , a 3 , a 4 , a 5 . .…”

“…The trend of projection lens is towards to short-focus length, wide field of view (FOV), decreasing F-number and high definition [1], and then the design and production of projection lens become more and more difficult. Generally, the projection lens is designed by refraction lens, however, when refraction objective lens is used in short-focus and wide field of view, the variety of aberrations is difficult to reduce because of rapid increase of chromatic aberration and axial coma aberration owing to wide field of view and F-number.…”

Design of objective lens with reflective spherical Fresnel zone plate

“…The performance of the objective lens has great influence on the performance of the system. Since the mid and late 1990s, the development trend of the objective lens has been towards short focus, wide angle of view, large Fresnel number and high definition [1], thus the design and production of the objective lens become more and more difficult. Generally, the objective lens is designed by a refraction lens; however, when the refraction objective lens is used in the condition of short focus and wide field angle, various kinds of aberration are difficult to reduce because of the rapid increase of the chromatic aberration and axial coma aberration owing to the large field of view and Fresnel number.…”