Optics: measuring and testing – Lens or reflective image former testing – Optical center – cylinder axis – or prism measuring or...
Reexamination Certificate
2001-03-26
2003-02-04
Mack, Ricky (Department: 2873)
Optics: measuring and testing
Lens or reflective image former testing
Optical center, cylinder axis, or prism measuring or...
C356S124500
Reexamination Certificate
active
06515739
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and a process for the spatially resolved determination of the refractive power distribution of an optical element.
BACKGROUND TECHNOLOGY
Progressive spectacle lenses are increasingly used in ophthalmic optics. They have several different surface refractive values, with a continuous transition between the various regions. In such lenses, for example those known from European Patent EP-A-0 039 497, at least one of their surfaces departs from a rotationally symmetrical shape.
The Hartmann process appears to be practicable for the quality testing of these aspheric lenses, since other methods, for example mechanical measuring processes with sensing heads or interferometric testing, are too slow, too expensive, or too sensitive to adjustments.
In the extrafocal method of J. Hartmann, dating from the year 1900, a diaphragm with two small holes placed symmetrically with respect to the optical axis is arranged close in front of the optical element to be tested. The focal length and the spherical aberration can be determined with two measurements in front of and behind the focal plane of the optical element, with varying hole spacing.
Testing of objectives according to Hartmann is known, for example, from German Patent DE 3318293 A1.
The Hartmann test in variants, and also the evaluation theory, are described in D. Malacara, Optical Shop Testing, Chapter 10, I. Ghoziel, Hartmann and Other Screen Tests, p. 323 ff., Wiley, New York, 1978.
A modified and simplified variant of the Hartmann test is described in OPTICAL ENGINEERING, Vol. 31, No. 7, July 1992, Bellingham, Wash., U.S., pp. 1551-1555, XP289274, D. Malacara et al., “Testing and centering of lenses by means of a Hartmann test with four holes”. The multi hole screen produces only four beam pencils there. This measurement method cannot be used for the measurement of spectacle lenses, since the spatial resolution is too low.
Measuring devices for the quality testing of spectacle lenses based on the Hartmann process are known from U.S. Pat. No. 5,825,476. With a multi hole screen or a lens array, the wavefront to be investigated is decomposed into individual beam pencils. These produce intensity peaks on a diffusing screen. By means of a reducing intermediate imaging, the intensity pattern is recorded by a CCD camera, for example. The distribution of refractive power of the lens being investigated is obtained with a subsequent computer unit from the analysis of the CCD image. The sharpness of the intensity peaks produced by the multi hole screen or the lens array is decreased by the use of the ground glass screen. Additional measurement errors are introduced by the reducing intermediate imaging of the ground glass screen on the detector.
European Patent EP 0 466 881 B1 describes wavefront measurement with many different coded arrangements of holes in the beam path. The requirements for stability and adjustment of the steppable multi hole screen in the beam path are then very high, in order to attain a consistent measurement result from several measurements. In order to increase the measurement accuracy, a calibration measurement would be required after each stepping of the multi hole screen. The measuring device contains a focusing optical system and a spatially resolving detector which is arranged in the neighborhood of the focal plane of the focusing system. The focusing optical system then has to be exceptionally well corrected in order to exert no negative influence on the wavefront to be investigated. The optical construction thus becomes very expensive.
SUMMARY OF THE INVENTION
The invention therefore has as its object an apparatus for the spatially resolved refractive power measurement of an optical element, having a simple construction and with which the highest accuracy with respect to spatial resolution can be realized in a short measurement time.
This object is attained with an apparatus for spatially resolved determination of refractive power distribution of an optical element, comprising a light source unit for illuminating said optical element with an extended pencil of rays, a first multi hole screen for production of a first number of beam pencils, a spatially resolving detector (
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), a computing unit, and a manipulator arranged either before or after said first multi hole screen, wherein said manipulator is controllable, a combination of said first multi hole screen manipulator is only transmissive for a second and said number of beam pencils, and said second number is smaller than said first number and greater than unity and a process for spatially resolved determination of refractive power distribution of an optical element comprising illuminating said optical element with an extended pencil of rays, producing a first number of beam pencils, reducing said first number of beam pencils to a second number of beam pencils, the second number being greater than unity, sensing spatially separated intensity peaks with a spatially resolving detector wherein the number of said spatially separated intensity peaks is equal to said second number of beam pencils, and calculating said refractive power distribution of the optical element with a computing unit. Advantageous developments of the invention will become apparent from the features of the invention.
The apparatus according to the invention accordingly includes a light source unit, a first multi hole screen and a controllable manipulator, a spatially resolving detector, and a computing unit. The light source unit includes a light source, such as for example a laser light source or a thermal lamp with a multi hole screen arranged in series with it, and reflective and/or refractive components for the production of an expanded pencil of rays with which the optical element to be investigated is illuminated. The optical element to be investigated locally influences the propagation of the pencil of rays. This influence can be measured with the combination of first multi hole screen and manipulator.
A first number of beam pencils is produced with the first multi hole screen. The multi hole screen selects beam pencils from the incident pencil of rays, in correspondence with the number of holes. The rays of each beam pencil represent the region of the optical element to be investigated through which they have passed. It is therefore possible to calculate back from the course of the individual beam pencils to the refractive power distribution of the optical element to be investigated. When the beam pencils strike the spatially resolving detector, they produce individual gaussian intensity peaks, the position of whose centers of gravity is determined by means of a subsequent evaluation algorithm in the computing unit. The refractive power distribution of the optical element to be investigated can be determined knowing the generation and detection points of a beam pencil. Evaluation algorithms are to be found, for example, in the publications of Malacara or in the cited documents.
In order to prevent the individual intensity peaks overlapping due to high positive local refractive power of the optical element to be investigated, a manipulator is provided which reduces the number of beam pencils. This manipulator can be an interchangeable second multi hole screen; electro-optical shutter blades, for example, a LCD (liquid crystal device) screen; or a micro-mirror array with individually controllable micro-mirrors, for example from Texas Instruments. With this controllable manipulator, it is possible to select the beam pencils such that the beam pencils do not intersect due to the locally varying refractive power distribution. The control is effected by the interchange of the multi hole screen when a multi hole screen is used, by the transparent/opaque switching of individual pixels in a LCD screen, or by the selective alignment of individual small mirrors in the case of a micr
Neuhaus Bruno
Volkenandt Harald
Carl-Zeiss-Stiftung
Mack Ricky
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