Optics: measuring and testing – Lens or reflective image former testing
Reexamination Certificate
2002-09-03
2004-07-06
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Lens or reflective image former testing
C356S125000
Reexamination Certificate
active
06760096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for evaluating the quality of a lens to be used in an optical apparatus such as a projector, which includes the steps of: illuminating imaging light including a test pattern for the measurement of resolution on a screen through the lens; and detecting the brightness of the test pattern image displayed on the screen by an image-capturing device having an image sensor, and calculating the evaluated value of resolution on the basis of the detected brightness level. Also, the present invention relates to a lens-evaluating apparatus using such a lens-evaluating method.
2. Description of the Related Art
Heretofore, there has been used a projector that comprises: a plurality of liquid crystal panels for modulating a plurality of color light beams for each of them on the basis of image information; a cross-dichroic prism for combining color light beams modulated by each of the liquid crystal panels; and a projector lens for forming a projecting image by extending and projecting a beam of light on a screen to form a projected image.
The projector lens used in such a conventional projector may cause variations in its optical characteristics such as image resolution, flare, chromatic aberration, curvature aberration, and the distribution of illuminance of the projected image due to variations in its manufacturing process or the like. Variations in the characteristics of the projector lens influence on the quality of an image displayed on a screen by the projector. Therefore, the characteristics of the lens are evaluated before the shipment of the lens and before the assembly of a projector with the lens.
Concretely, for example, the resolution of the projector lens is evaluated by forming a test pattern for the resolution measurement on a test sheet, illuminating light on the test pattern to generate imaging light that includes a test pattern image, introducing the imaging light into a projector lens provided as a testing sample to be evaluated, and projecting the imaging light from the projector lens on the screen. Then, the test pattern image displayed on the screen is detected by an image capturing apparatus using an image sensor such as a charge coupled device (CCD), followed by subjecting the detected image using a computer or the like to evaluate the resolution of the projector lens.
Similarly, when the projector lens is evaluated for the generation of flare, it can be performed using a flare-testing pattern formed on a test sheet. When the projector lens is evaluated for the generation of chromatic aberration, a color beam filters can be used. Each of the color light beam filters has a function of extracting a color light beam which corresponds to a specific color included in the light emitted from a light source. In other words, the light beam passed through the color beam filters of red, green, and blue illuminates a screen to represent an image of test pattern. Then, the image displayed on the screen is detected by an image-capturing device using an image sensor such as CCD. Subsequently, the detected image is subjected to an arithmetic operation by a computer or the like to evaluate the chromatic aberration of the projector lens.
Furthermore, for evaluating the curvature aberration of the projector lens and the illuminating distribution of a projected image, an image of test pattern displayed on the screen is visually observed to check the qualities.
Conventionally, a basic lens has been applied in the method for evaluating the quality of a lens. In such a method, the deviation between the basic lens and a target lens to be evaluated is measured to evaluate the quality of the target lens. Specifically, the basic lens that shows an average level of each characteristic of the lens is used for the evaluation, where a test sheet is adjusted to be positioned on the back-focal surface of the basic lens. Then, an imaging beam illuminates a screen through the basic lens. Subsequently, an image sensor positioned on each of four corners of the screen scans a test pattern formed on the test sheet by means of a pattern matching. The test pattern is imaged and is then provided image data. From the resulting image data, it is judged whether focus is achieved using a specific indexical value (edge strength) of the test pattern image to check the quality of focusing. As a result, four indexical values can be obtained. Depending on the resulting four indexical values, a six-axis adjusting part is controlled to adjust the spatial arrangement of the test sheet (test pattern) such that these four indexical values become almost equal to each other and become the maximum values. Subsequently, in a state of fixing the test sheet being justified using the basic lens, the target lens to be evaluated is subjected to the characteristic evaluation of the lens.
Therefore, the evaluation of optical characteristics of the lens in quick motion can be performed because of no need to adjust the focus of the target lens on the test sheet.
However, the back-focal surface of the actual lens is curved. Such a curvature of the back focus of the lens is unique to an individual lens. In other words, the positioning of the test sheet is performed using the basic lens, and the evaluation of the quality of each lens is performed on the position of the test sheet being adjusted by the basic lens. For the evaluation of optical characteristics of each lens, there is a problem that the quality of the lens can be evaluated under the conditions in which the test sheet (test pattern) and the back-focal surface of each lens are misaligned with respect to each other.
If the evaluations are carried out to check the curvature aberration of the projector lens and the illuminating distribution of the projected image by visually observing the projected image, the exact characteristic value of the project lens cannot be obtained and a criterion of judgment whether the characteristic value is acceptable or not is obscure.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a method for properly evaluating the characteristics of a lens and a lens-evaluating apparatus using such a method.
A method for evaluating the quality of a lens (also referred to as a lens-evaluating method) in accordance with present invention comprising: illuminating imaging light on a screen through the lens to form a projected image, where the imaging light having a test-pattern image is generated using a test sheet on which a test pattern for measuring a resolution of the lens is formed to evaluate the resolution; detecting a brightness of the test-pattern image displayed on the screen by an image-capturing device using an imaging sensor; calculating an input level on the basis of the detected brightness of the test-pattern image; and calculating an evaluated value of resolution, and adjusting a position of the test sheet to a position corresponding to a focus of the lens by detecting the test-pattern image while moving the test sheet back and forth in the direction along an optical axis of the lens.
Here, the imaging element may be selected from a CCD (charge-coupled device) sensor, a MOS (metal oxide semiconductor) sensor, and so on. Also, the image-capturing device may be a device for obtaining image data, such as a video capture board that receives an output from the imaging element and converts it into an image signal to be transmitted to a computer.
According to the present invention, as the method has the step of adjusting the focus of the projector lens, the evaluated value of resolution can be calculated on the basis of imaging light detected under the condition in which the position of the test sheet is adjusted to the focal position of the test lens. Therefore, it becomes possible to correctly calculate the evaluated value of resolution by preventing the image from out of focus or the like due to a bend in the back-focal surface of the lens or the like.
In addition, for focal adjustment of each lens, the deviation obtained by
Kitabayashi Masashi
Kojima Koichi
Umemura Shunji
Font Frank G.
Nguyen Sang H.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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