Optics: measuring and testing – Lens or reflective image former testing
Reexamination Certificate
2002-07-08
2004-09-07
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Lens or reflective image former testing
Reexamination Certificate
active
06788401
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates a lens inspection apparatus and an inspection sheet.
2. Description of Related Art
Recently, projectors have been used which include a plurality of liquid crystal panels for modulating a plurality of colored light beams according to image information, a crossed dichroic prism for combining the colored light beams modulated by the corresponding liquid crystal panels, and a projection lens for enlarging and projecting the light beams combined by the prism so as to form a projection image. The optical characteristics, such as image resolution and chromatic aberration, of the projection lens used in the projectors sometimes vary, for example, depending on variations in the production processes. Since the variations in optical characteristics of the projection lens have an influence on the quality of the image displayed by the projector, the resolution of the lenses is evaluated before the lenses are shipped by the lens manufacturer and before the lenses are assembled into the projectors.
More specifically, a test pattern for resolution measurement is formed on an inspection sheet, image light containing the test pattern is introduced into a projection lens by irradiating the test pattern with light, and the image supplied from the projection lens is projected onto a screen. Then, the image of the test pattern projected on the screen is detected by an image capture apparatus using an image pickup device, such as a CCD (Charge Coupled Device), and the image detected by the apparatus is subjected to image processing by a computer or the like, thereby evaluating the resolution of the projection lens. Since the test pattern includes a plurality of small patterns of a predetermined size, the plurality of small patterns are projected on the screen. The image pickup device sequentially moves over the small pattern images projected on the screen, and captures the images at the corresponding positions.
SUMMARY OF THE INVENTION
Test patterns to be formed on known inspection sheets are quite small so that the outer size thereof is, for example, approximately 10.8 mm×14.4 mm. These test patterns can include a plurality of small patterns, as described above, and the outer size of the small patterns is even smaller, for example, 795 &mgr;m×1074 &mgr;m. Since the test patterns of the inspection sheets have such a quite fine structure, they are manufactured in a process similar to a semiconductor manufacturing process. That is, first, chromium (Cr) is evaporated onto a glass substrate after a mask having a predetermined test pattern is produced beforehand. Then, a photoresist (photosensitive resin) is applied on the chromium on the glass substrate, and is irradiated with ultraviolet rays through the above mask. Subsequently, portions of the photoresist irradiated with the ultraviolet rays are removed with a predetermined solvent. In this way, the mask is transferred onto the photoresist. By then subjecting the chromium to etching with the photoresist used as a mask, a chromium test pattern is formed on the glass substrate.
A plurality of types of inspection sheets are necessary in accordance with the outer sizes of liquid crystal panels used in the projector. Since a plurality of types of inspection sheets are manufactured through such a process, the cost of the inspection sheets is increased. Since the resolutions of a plurality of small patterns formed in the test pattern are evaluated while moving the image pickup device to the image positions of the small patterns, as described above, it takes a long time to move and place the image pickup device at predetermined positions, and fast inspection is impossible.
Accordingly, an object of the present invention is to provide a lens inspection apparatus and an inspection sheet that make it possible to easily evaluate the resolution of a lens at low cost.
A lens inspection apparatus of the present invention inspects a lens in order to evaluate the resolution of the lens by projecting image light containing a test pattern for resolution measurement onto a screen through the lens, and displaying an image of the test pattern for resolution measurement on the screen. The lens inspection apparatus can include an inspection sheet having the test pattern for resolution measurement, an inspection-sheet holder for holding the inspection sheet, a light source for introducing a light beam to the test pattern of the inspection sheet held by the inspection-sheet holder, and an image-light detecting section having an image pickup device for capturing an image projected on the screen through the inspection sheet. The test pattern can include a measuring region in which linear light-shielding portions are arranged in stripes in order for transmitted light to have a predetermined spatial frequency, and the inspection-sheet holder includes a holder body having a light-transmissive section corresponding to the test pattern of the inspection sheet for positioning the inspection sheet at a focal position of the lens, and a rotary holding portion for holding the inspection sheet so that the inspection sheet rotates in a plane relative to the holder body.
As the image pickup device, image pickup devices, such as CCDs and MOS (Metal Oxide Semiconductor) devices, may be used.
The image-light detection section may include the above-described image pickup device, an image data generating device, such as a video capture board, for receiving an output from the image pickup device and for converting the output into image signals for a computer, and a computer for processing the image signals. The computer may include a program running under an OS (Operating System) for controlling the operation of the computer, and the program may include, for example, a program for evaluating the resolution, the chromatic aberration, and the like.
While the predetermined spatial frequency may be arbitrarily determined, for example, it can be set to be within the range of 20 lines per millimeter to 80 lines per millimeter.
In the lens inspection apparatus of the present invention, for example, when a light beam is emitted from the light source after the inspection sheet is held in the inspection-sheet holder so that the light-shielding portions of the test pattern arranged in stripes extend in the vertical direction (upward-downward direction), the light beam travels through the inspection sheet and the projection lens, and a test pattern image in which the light-shielding portions extend in the vertical direction is projected onto the screen. By capturing the projected image with the image pickup device, and then detecting the captured image with the image detecting section, the resolution of the projection lens can be evaluated.
Next, the rotary holding portion can be rotated in a plane relative to the holder body, and is fixed at a position such that the direction of the light-shielding portions is different from the above direction (vertical direction). For example, the rotary holding portion is rotated by 90°, and is fixed so that the light-shielding portions extend in the horizontal direction (rightward-leftward direction). In this state, the resolution of the projection lens can be evaluated in a manner similar to the above.
By changing the orientation of the test pattern by rotating the rotary holding portion in a plane after loading the inspection sheet having the test pattern into the inspection-sheet holder, as described above, the resolution of the projection lens can be easily evaluated while one type of test pattern, in which the light-shielding portions extend in different directions, for example, in two directions, that is, the vertical direction and the horizontal direction, is projected onto the screen. In this way, the number of types of inspection sheets to be prepared can be reduced, and the cost of the inspection sheets can be reduced. In this case, simply by rotating the rotary holding portion, the resolution evaluation can be easily switched to a resolution evaluation with an inspec
Kitabayashi Masashi
Kojima Koichi
Oliff & Berridg,e PLC
Pham Hoa Q.
Seiko Epson Corporation
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