Optics: measuring and testing – For light transmission or absorption – Of photographic film
Reexamination Certificate
1998-12-23
2001-05-22
Font, Frank G. (Department: 2877)
Optics: measuring and testing
For light transmission or absorption
Of photographic film
C356S432000, C356S224000
Reexamination Certificate
active
06236461
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a laser sensitometer designed to expose light sensitive material or other imaging surfaces to a series of intensity levels and at various wavelengths.
BACKGROUND OF THE INVENTION
Sensitometers are well known in the photographic art as apparatus for making sensitometric test strips from light-sensitive material (such as photographic paper or film) to determine the resolution response from the material. A sensitometer generally comprises a light source and means for producing a graded series of exposures (also referred to as line exposures) of the light-sensitive material being tested, such as an optical wedge having a series of steps of known absorbing power.
U.S. Pat. No. 3,677,653 (Hocker) teaches a sensitometer wherein a laser and a negative lens forward of the laser are used as the means for producing a divergent coherent monochromatic light beam. When it is desired to make a sensitometric test strip of the light-sensitive material, the light-sensitive material is placed in contact with the optical wedge. The laser directs a beam through the steps of various density of the optical wedge and impinge upon the front surface of the light-sensitive material being tested. The light-sensitive material is then developed by conventional means and the characteristics of the light-sensitive material are determined by methods and apparatus already known in the art. While such an apparatus may be suitable for its intended purpose, the dimensions of the divergent laser beam change rapidly as a function of distance, thus making it difficult to control the exposure densities.
Other known methods of producing a graded series of exposures (also referred to as line exposures) of the light-sensitive material involve the displacement of a light beam (or laser beam) following reflection on a rotating prism or rotating polygon. A rapid scanning of the light beam caused by the rotating prism or polygon also produces a exposure time. U.S. Pat. No. 5,053,619 (Arimoto) relates to an optical system using rotating polygons. Rotating prisms and/or rotating polygons are expensive optomechanical components. Further, their use requires mechanical rotation at very high rotational speeds, for example, in the range of 20,000-40,000 revolutions/minute, and such high rotational speeds introduce/increase mechanical maintenance.
A known method to vary and control the laser intensity on an exposure is the use an acuosto-optical modulator (AOM). However, the use of AOMs imposes beam focusing constraints, energy density limitations, and require sophisticated electronics for control. Polygon mirrors, used in optical scanning, and AOMs are described in the “Handbook of Optics”, Volume II, edited by M. Bass, McGraw-Hill, N.Y., 1995.
Accordingly, a need continues to exist for a reliable laser sensitometer which has an optical structure that is compact, optically rugged, and does not incorporate a rotating prism, rotating polygon, or an AOM.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved laser sensitometer.
Another object of the invention is to provide such a laser sensitometer which has an optical structure that is compact, optically rugged, and does not incorporate rotating prisms or polygons, nor AOMs.
Still another object of the invention is to provide such a laser sensitometer which has reduced mechanical maintenance.
These objects are given only by way of illustrative example. Thus, other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. The invention is defined by the appended claims.
According to one aspect of the invention, there is provided an electro-optical apparatus including a light source, beam shaping optics, and a rotatable polarizer. The light source is adapted to provide a Gaussian beam of light directed along an optical axis. The beam shaping optics are disposed in the optical path and adapted to expand the Gaussian beam of light into an elongated beam of light and to project the elongated beam of light along the optical axis toward a sample. The rotatable polarizer, disposed in the optical path intermediate the light source and the beam shaping optics, is rotated to vary the intensity level of the beam of light.
According to another aspect of the present invention, there is provided a method for exposing a sample of light sensitive material to provide a graded series of exposures of different intensity levels. The method includes the steps of: generating a Gaussian beam of light directed along an optical axis toward a sample of light sensitive material; directing the generated Gaussian beam of light through a rotatable polarizer; expanding the polarized beam of light into an elongated beam of light; projecting the elongated beam of light onto the sample; displacing the sample in a plane transverse to the optical axis and the plane of propagation; and repeat the steps of directing, expanding, projecting, and displacing until an exposure area with a desired dimension is obtained.
Accordingly, the present invention discloses an optical structure that does not employ an AOM or a high speed rotating prism or polygon. As such, the present invention provides a reliable, compact, optically rugged, simple, and reduced cost laser sensitometer.
REFERENCES:
patent: 3677653 (1972-07-01), Hocker et al.
patent: 5053619 (1991-10-01), Arimoto
patent: 5255069 (1993-10-01), Duarte
“On a Generalized Interference Equation and Interferometric Measuremets” published in Optics Communications, vol. 103, No. 1, 2 by F.J. Duarte pp. 8-14.
“Interferometric Imaging” published in Tunable Laser Applications by F.J. Duarte, pp. 153-177.
“Narrow-Linewidth Laser Oscillators and Intracavity Dispersion” published in Tunable Lasers Handbook by F.J. Duarte, pp. 9-32.
Eastman Kodak Company
Font Frank G.
Parulski Susan L.
Ratliff Reginald D.
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