WO1996005503A1

WO1996005503A1 - Device for testing optical elements

Info

Publication number: WO1996005503A1
Application number: PCT/EP1995/003180
Authority: WO
Inventors: Shmuel Liran; Amit Stekel; Moshe Lapidot
Original assignee: Rapaport, Erich; Optomic Technologies Corporation Ltd.
Priority date: 1994-08-10
Filing date: 1995-08-10
Publication date: 1996-02-22
Also published as: IL110618A0; IL110618A; AU3344395A

Abstract

A system and method for the evaluation of optical elements in order to grade these according to predetermined criteria of quality, especially suited for optical elements devoid of optical power. The examined optical element (22) is illuminated with a wide-angle beam of white light, which is passed via a diffusing screen (12) having a masked out circular central area (13), and a relay lens (14), and there is also provided on the optical axis an imaging lens (16) which receives only light scattered from defects of the optical element, and there are provided means for evaluating these light signals so as to grade the said optical elements.

Description

DESCRIPTION

DEVICE FOR TESTING OPTICAL ELEMENTS

FIELD OF THE INVENTION

The invention relates to a system and method for the rapid

inspection of optical elements devoid of optical power. The

inspection reveals the presence of defects of the transparent inspected product, such as surface flaws (scratches, cracks, stains, etc.) and also internal defects, such as bubbles or streaks.

BACKGROUND OF THE INVENTION

There exist a wide variety of devices which are intended for the inspection of optical elements, and especially optically active elements such as optical lenses and the like. Most of these are based on the scanning of the lens, and on the detection of any external or internal defects, generally by observing light scattering resulting from such defects. U.S. Patent No. 4,814,844 is based on dot-scanning of the lens, and detection of light refracted by irregularities. U.S. Patent 3,988,068 relates to a device for detecting defects of ophthalmic lenses, and this is based on the passage of a narrow beam of light through the lens and detecting light due to scattering by defects, by an array of photodetectors arranged around the edge of the lens, which would not be reached by light pulses, in the absence of such defects. According to this patent the lens surface is scanned by the narrow light beam, and means are provided for quantitizing the results of such scans. SUMMARY OF THE INVENTION

There is provided a system for the rapid inspection or optical elements devoid of optical power, There is also provided a method for effecting such inspections and for the evaluation of the results, The system of the invention is based on the provision of an

illuminating beam which passes via a relay lens and through the optical element to be inspected, such as a lens of sunglasses or any other element devoid of optical power, there being provided a diffusing screen with a central dark circular area, and an imaging lens on the axis of the relay lens and optical element, so that the image of the dark circular area prevents direct light from the light source from reaching the imaging lens. Only light scattered by any defects of the examined optical element reaches this lens and is discerned and evaluated. Generally the imaging lens is part of a video camera, but other devices, such as any CCD array or the like may be used.

This "dark field illumination" results in that light scattered by surface defects or by internal defects, such as bubbles, non-trans, parent defects and the like reach the imaging lens and such light is indicative of such defects and their severity.

Means can be provided for automatically evaluating the number, location and severity of defects of the optical element, and criteria can be provided for discarding any optical element which is of a qualtity inferior to that predetermined by such criteria. The invention also provided a method for the inspection of

transparent optical elements devoid of optical power, which

comprises illuminating the optical element by a light beam via a relay lens where the light beam from the light source passes via a diffusing screen with a central dark circular area and imaging the diffusing screen on an imaging lens, so that the dark circular area blacks out any direct light from the light source to the imaging lens, light scattered by defects of the optical element reaching the imaging lens, and through it suitable detection means, providing information on the presence or absence of defects and their severity.

BRIEF DESCRIPTION OF THE DRAWINGS:

The Invention is illustrated with reference to the enclose schematical perspective view, which is not according to scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Thq invention is illustrated by way of example only with reference to the enclosed schematical perspective view illustrating the principles of a system of the invention.

As shown in Fig. 1, the system, for the rapid inspection of optical element 15, which is devoid of optical power, comprises in combination a 1 iglit source 11 in front of which there is located a diffusing screen 12, with a central dark circular area 13, so that light from source 11 is diffused through screen 12 and passes through a relay lens 14, and through said optical element 15, onto imaging lens 16 which may be part of a video camera 17. The light which passes the diffusing screen 12 has a gradually varying intensity and covers a wide solid angle. The light beam passes via relay lens 14, and this results in the focusing of the circular dark area 13 at the aperture plane 18, and the dimensions are such that the image of the circular area 13 covers entirely the entrance pupil of the imaging lens 16. The path of light rays, from the light source 11, illustrates the principle used: the rays 19 which emerge from the contour of 13 reach the contour of the image of this dark area at the aperture plane 18 of imaging lens 16, Light rays 20 which emerge from the diffusing screen 12 in parallel, pass via relay lens 14, and converge as shown by 21 to test point 22 of tested lens 15, and are scattered in the direction shown by 23.

Light rays 20 are blocked by dark area 13 so that they converge from the relay lens 14 in the direction 24 to test point 22, of the element 15 which is illuminated by a wide solid angle of rays, of from about 1 degree to about 40 degrees, except for the narrow solid angle in the -/+ 1 degree range, in the direction normal to the components surface. If at the location of the test point, 22 there exists a defect of the optical element 15, the result is a scattering of light rays, part of which the imaging lens 16. Thus, there is formed an image on the surface of lens 16, which represents such defect. Various types of defects are sensitive to different angles of illumination, and thus it is very important to provide a wide range of illumination angles. "Illumination angle" is defined as the angle between the surface normal of the test lens, 15, and the specific ray of illumination, impinging on the surface element, Most of the flaws are detectable when illuminated at a small angle of illumination, and such are easily attainable by the system of the invention. It is one of the constraints of the system that a narrow depth of field (D.O.F.) is needed.

A possible source of errors is reflections in the system. There exist two main types: the first is an internal reflection between the two surfaces of the relay lens 14, and the second is reflection between relay lens 14 and test object 15. A small tilt of the relay lens 14 serves to resolve this problem by deflecting various reflections away from the optical axis of the lens 16 and camera 17. Ihls will not influence direct rays except for negligible distortions of the image dark area 13.

Claims

CLAIMS :

1. A method for the rapid inspection of optical elements devoid of optical power, which comprises illuminating such an optical element with a wide angle optical beam, originating from a strong light source, which is first passed via a diffusing screen and a relay lens, said diffusing screen having a central dark circular area, there being arranged on the optical axis of the system an imaging lens, which is masked out from direct illumination due to the said central dark area said imaging lens receiving only signals resulting from external or internal defects of the examined optical element, means being provided for evaluating such signals in order to determine whether the optical element can be used or is to be discarded.

2. A method according to claim 1, where the optical element is a lens devoid of optical power.

3. A method according to claim 1 or 2, where the light beam illuminating the optical element has a solid angle of from about 1 to about 40 degrees, in the direction normal to the surface of the optical element.

4. A method according to any of claims 1 to 3 where the relay lens tilted at a small angle respective the optical axis of the system.

5. A system for the rapid examination and grading of optical elements devoid of optical power to detect and evaluate surface and internal defects, which comprises, arranged along an optical axis, a sequence of a source of light, illuminating a relay lens via a diffusing screen, at the center of which there fs provided a dark circular area, light passing said relay lens being directed at the optical element under test, and incident on same ih a wide spatial angle, there being provided an imaging lens which is shielded from direct illumination by said dark circular area, and wirich is reached only by light scattered by imperfections of the optical element, means being provided for evaluating such light siynαls reaching the imaging lens.