# US 5,708,532 A · Double-sided telecentric measurement objective

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- Number: US 5,708,532 A
- Document ID: US5708532A
- Status: Granted
- Kind: A
- Application number: 08/659,044
- Filed: 1996-06-03
- Granted: 1998-01-13
- Earliest claimed: 1995-06-03
- Assignees: Jos. Schneider Optische Werke Kreuznach GmbH & Co. KG
- Inventors: Rolf Wartmann
- Web page: https://patentgrep.com/patent/US5708532A

## CPC

- G02B 13/22: Telecentric objectives or lens systems
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A double sided telecentic measurement objective for contactless length measurement in two-dimensional and three-dimensional space. The objective has an image-side optical system consisting of three elements equivalent to those of an object-side optical system but in the reverse order, including a cemented positively refracting lens element turned toward the object of image respectively, a collecting lens spaced by an air gap from the cemented lens, and a dispersive meniscus spaced by an air gap from the collecting lens. The widths of the air gaps between the collecting lenses and the meniscus are substantially greater than the widths of air gaps between the cemented lens elements and the collecting lenses.

## Claims

### Claim 1

A double-sided telecentric measurement objective for contactless length measurement in two-dimensional and three-dimensional space, said objective comprising:
two optical systems, each comprising three lenses aligned along an optical axis and constituted of an object-side optical system and an image-side optical system,
said object-side optical system having in succession from a side turned toward an object:
a cemented positively refracting lens element and a dispersive cemented surface formed by a convergent lens L.sub.1 with radii of curvature r.sub.1 and r.sub.2 and a thickness d.sub.1 and a divergent lens L.sub.2 with radii of curvature r.sub.2 and r.sub.3 and a thickness d.sub.2,
a collecting lens L.sub.3 spaced by an air gap of a thickness d.sub.3 from said cemented lens element and having radii of curvature r.sub.4 and r.sub.5 and a thickness d.sub.4 of a highly refractive crown glass, and
a dispersive meniscus lens L.sub.4 spaced by an air gap of thickness d.sub.5 from said collecting lens and having radii of curvature of r.sub.6 and r.sub.7 and a thickness d.sub.6 ;
and an image-side optical system having in succession from a side turned away from said object:
a cemented positively refracting lens element and a dispersive cemented surface formed by a convergent lens L.sub.1 ' with radii of curvature r.sub.1 ' and r.sub.2 ' and a thickness d.sub.1 ' and a divergent lens L.sub.2 ' with radii of curvature r.sub.2 ' and r.sub.3 ' and a thickness d.sub.2 ',
a collecting lens L.sub.3 ' spaced by an air gap of a thickness d.sub.3 ' from said cemented lens element and having radii of curvature r.sub.4 ' and r.sub.5 ' and a thickness d.sub.4 ' of a highly refractive crown glass, and
a dispersive meniscus lens L.sub.4 ' spaced by an air gap of thickness d.sub.5 ' from said collecting lens and having radii of curvature of r.sub.6 ' and r.sub.7 ' and a thickness d.sub.6 ' with a convex side turned away from said object;
widths of air gaps between the respective collecting lenses and the respective meniscuses being substantially greater than widths of air gaps between the cemented lens elements and the respective collecting lenses;
a back focal point of said object-side optical system coinciding with a front focal point of said image-side optical system so that a reproduction scale of the objective is equal to a ratio of front and back focal lengths of said optical systems, said image-side optical system having substantially the following numerical parameters wherein n.sub.e and .nu..sub.e are respectively the refractive indices and Abbe numbers of the respective lenses:
______________________________________ Lens Radius Thickness n.sub.e .upsilon..sub.e ______________________________________ r.sub.1 ' = 130.882 L.sub.1 ' d.sub.1 ' = 9.60 1.4891 70.2 r.sub.2 ' = -22.140 L.sub.2 ' d.sub.2 ' = 2.00 1.6072 37.8 r.sub.3 ' = -127.464 d.sub.3 ' = 3.10 r.sub.4 ' = 40.965 L.sub.3 ' d.sub.4 ' = 5.70 1.6413 55.1 r.sub.5 ' = -597.046 d.sub.5 ' = 13.50 r.sub.6 ' = 28.247 L.sub.4 ' d.sub.6 ' = 11.39 1.5848 40.6 r.sub.7 ' = 15.845 ______________________________________
focal length: 57
distance to back focal point: 23.20.

### Claim 2 (depends on 1)

The objective defined in claim 1 wherein the lenses L.sub.1 through L.sub.4 have radii of curvature r.sub.1 through r.sub.7 and thicknesses d.sub.1 ' through d.sub.6, refractive indices and Abbe numbers corresponding to those of the lenses L.sub.1 ' to L.sub.4 ' for the radii r.sub.1 ' through r.sub.7 ' and thicknesses d.sub.1 ' through d.sub.6 ', and the respective refractive indices and Abbe numbers.

### Claim 3 (depends on 1)

The objective defined in claim 1 wherein the object-side optical system has the following numerical parameter:
______________________________________ Lens Radius Thickness n.sub.e .upsilon..sub.e ______________________________________ r.sub.1 = 163.039 L.sub.1 d.sub.1 = 12.00 1.4891 70.2 r.sub.2 = -42.468 L.sub.2 d.sub.2 = 4.00 1.6072 37.8 r.sub.3 = -219.485 d.sub.3 = 14.72 r.sub.4 = 53.840 L.sub.3 d.sub.4 = 11.40 1.6413 55.1 r.sub.5 = -96.899 d.sub.5 = 42.58 r.sub.6 = 38.188 L.sub.4 d.sub.6 = 22.78 1.5848 40.6 r.sub.7 = 20.358 ______________________________________
focal length: 114
distance to back focal point: 28.07.

### Claim 4 (depends on 1)

The objective defined in claim 1 wherein said object-side optical system has the following numerical parameter:
______________________________________ Lens Radius Thickness n.sub.e .upsilon..sub.e ______________________________________ r.sub.1 = 243,547 L.sub.1 d.sub.1 = 17.00 1.4996 66.7 r.sub.2 = -88.326 L.sub.2 d.sub.2 = 8.60 1.6072 37.8 r.sub.3 = -342.441 d.sub.3 = 82.40 r.sub.4 = 72.157 L.sub.3 d.sub.4 = 12.00 1.6413 55.1 r.sub.5 = -78.537 d.sub.5 = 163.70 r.sub.6 = 47.746 L.sub.4 d.sub.6 = 22.80 1.5848 40.6 r.sub.7 = 29.641 ______________________________________
focal length: 228
distance to back focal point: 4.75.