Variable Pitch Patent (PDF)


Chromatic Method Patent (PDF)


1987 Basic Method Patent (PDF)


Diffraction Range Finding System

Thomas D. Ditto
a.k.a Thomas D. DeWitt

1. The purpose of the Variable Pitch invention

We improve the performance of a diffraction range finder instrument by using a diffraction grating with variable pitch. Improvements include increased resolution, better linearity, greater target to instrument stand-off, a lowered occlusion liability and a more compact instrument size. Variable pitch enables a new form of 3D microscopy.

2. The purpose of the Chromatic Method

We improve the performance of the diffraction range finder by correlating wavelength to distance. A polychromatic source is ranged. A color sensor or a spectrometer is used to make the range reading. The improvement increases speed of acquisition. It exploits readily available and inexpensive components. In some applications it overcomes perspective foreshortening, because the size of a spectrum increases as a target recedes, providing a plurality of samples that can be averaged.

3. Background of the Invention

Diffraction range finders are devices which determine distance by measuring the displacement of the higher-order diffraction images of a target relative to the zero- order diffraction image of the same target. A basic method patent , describes the process and illustrates a preferred embodiment. Upon learning in December 1986 that the U.S. Patent had been allowed, the inventor, Thomas DeWitt, applied for foreign patents and made a public disclosure to a knowledgeable group of engineers. Other public disclosures by the inventor followed. Research funding was sought by the inventor through corporate sponsors. Grants from the National Science Foundation and from the New York State Science and Technology Foundation resulted in two more publications co-authored by Mr. DeWitt and Dr. Douglas A. Lyon which can be found at

A range finding method using diffraction gratings

3D microscope using diffraction gratings

The basic method Rangefinding by Diffraction patent can be found on Google Patents Thomas De Witt, Range Finding by Diffraction, U.S. Patent 4,678,324, July 7, 1987

International patents issued: England (No. 0,343,158), France (No. 87901777.0), Germany (No. P3789901.5), Sweden (No. 87901777.0), Switzerland (No. 675,299) and Japan (No. 2528921).

Tom DeWitt, "Novel methods for the acquisition and display of three-dimensional surfaces," Optical and Digital Pattern Recognition, 1987, SPIE, Vol. 754, pp. 55-63

Tom DeWitt, "Range Finding with Diffraction Gratings," Advanced Imaging, July/August 1988, No. 12, p. A50 ff.

Tom DeWitt, "Diffraction Range Finding for Machine Vision," Proceedings of Robotics 12/Vision 88, 1988, SME, Vol. 1, Section 5, pp. 139-150

Tom DeWitt, "3D Image Acquisition by Diffraction Profilometry," Paper Summaries of SPSE's 42nd Annual Conference, May 1989, pp. 51-54

Tom DeWitt, A Guide to 3-D Surface Acquisition, Proceedings of the Tenth Symposium on Small Computers in the Arts, SCAN 90, Nov. 1990, pp. 40-46

Raytel, Inc. of Troy, NY applied for an NSF SBIR in 1985, '86, and '87. DeWitt Brothers Tool Company, Inc. applied in 1991 and 1992. DeWitt Brothers Tool Company was granted a Phase I SBIR in 1994 , III 92-61621, 3-D Machine Vision by the Diffraction Method ($50,000 over 6 months), and a Phase II SBIR, DMI-9420321 A Hand-Held Three Dimensional Scanner ($300,000 over 2 years), was granted in 1995.

New York State Science and Technology Foundation grant to DeWitt Brothers Tool Company, Inc. SBI-94062 3-D Metrology in Cavities, Recesses and Holes by the Diffraction Method ($10,000 over 6 months) 1994

Thomas D. DeWitt and Douglas A. Lyon, A Range Finding Method Using Diffraction Gratings, Applied Optics, May 10, 1995, Vol. 34 No. 14, pp. 2510-2521

Thomas D. DeWitt and Douglas A. Lyon, "Three-dimensional microscope using diffraction gratings," Three-Dimensional and Unconventional Imaging for Industrial Inspection and Metrology, SPIE, Vol. 2599, pp. 228-239

Tom Ditto and Douglas A. Lyon, "Moly a prototype handheld three-dimensional digitizer with diffraction optics," Three-Dimensional Image Capture and Applications II, January 1999, SPIE Vol 3640 paper 08, PDF file 335KB Moly disclosure

Tom Ditto and Douglas A. Lyon, "Moly a prototype handheld three-dimensional digitizer with diffraction optics," Optical Engineering, January 2000, Vol 39 No. 1, pp. 68-78

Tom Ditto and Douglas A. Lyon, "Anamorphic magnification using a chirped grating in grazing incidence mode" Conference on Machine Vision and Three-Dimensional Imaging Systems for Inspection and Metrology, October 2000, SPIE Vol 4189 paper 19. PDF file 770KB Grazing incidence chirp disclosure

Tom Ditto, "Compact 3D Profilometer with Grazing Incidence Diffraction Optics," Proceedings of the Third International Conference on 3-D Digital Imaging and Modeling, IEEE Computer Society, PR00984, June 2001 pp. 73-80, PDF file 445KB Includes use of CD or DVD as grazing incidence grating