JPH04309834A - Lens inspection device - Google Patents

Abstract

PURPOSE:To enable lens inspection in an ordinary factory office room by picking up an axial position of a chart by means of a telecamera through a lens to be inspected, picking up non-axial positions of the chart on inclined optical paths by means of another telecameras, and observing whole output images by means of television monitors. CONSTITUTION:An image forming lens 4a forms an image by receiving inversely projecting light flux from a position of a chart 1 situated on its optical axis, and image forming lenses 4b and 4c form images by receiving inversely projecting light fluxes from non-axial positions of the chart 1. Furthermore, among the light fluxes from the chart 1 illuminated from a light source 3 through a diffusion plate 2, the light flux from a position 1a in the vicinity of the optical axis receives a converging action by means of a lens A to be inspected, and an image is formed on an image pickup element 5a by means of the lens 4a, and is projected on a television monitor 6a. Further, as for the light fluxes from a peripheral position 1b and so on, images are formed respectively on image forming elements 5b and 5c by means of the lenses 4b and 4c, and are projected on television monitors 6b and 6c. Thereby, an inspector can judge synthetically in an ordinary office room by observing the images on the television monitors 6a, 6b and 6c.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for testing the performance of lenses.

0002

2. Description of the Related Art Conventional lens inspection apparatus include a back projection type apparatus using a projector. This is a method in which a chart, a condenser lens, and a light source are arranged on the image plane side of the test lens, and the image of the chart is projected onto a screen in front of the test lens.

This method has the advantage that the examiner can examine the entire chart image on the screen at once, but it requires the entire room to be completely dark, which puts a strain on the examiner's eyes. Furthermore, when the focal length of the lens to be tested is long, at least two examiners are required on the screen side and on the side of the test lens. Furthermore, a large darkroom is required in terms of space, which hinders efforts to save labor and reduce costs.

0004

[Problems to be Solved by the Invention] The present invention provides a lens inspection device that can be used in a normal living room in a factory, and further provides a device that is comparable in performance to conventional inspection devices. It is something.

[0005]

[Means for Solving the Problems] A test chart arranged on the image plane side of a test lens, an illumination means for illuminating the chart, and a television imaging means for imaging the axial position of the chart through the test lens. , a television imaging means for imaging the off-axis position (periphery) of the chart, and a television monitor for observing the output images of the respective television imaging means.

Also, focusing on performance, a chart is placed on the image plane side of the test lens, a light beam is back-projected onto the chart using a light source, and an image is formed using an imaging lens. The chart image on the image sensor is observed on a TV monitor. Maximum number of stripes to inspect (1
(counting black and white as one per mm) is N, the number of pixels per 1 mm of the image sensor is M, and the focal length of the imaging lens is F, then 3 (2N/M)>F/f>0 .9(2N/M), and includes at least an imaging lens for the chart at the center of the optical axis of the test lens and an imaging lens for the surrounding charts.

[0007]

[Embodiment] Before explaining the specific structure of the embodiment, matters related to the above-mentioned formula will be explained.

First, the imaging position of the back-projected light beam may be set at infinity, but since the object distance that normally provides the best performance of the tested lens is a finite distance, it is better to set it near that finite distance. However, it is better to be farther away than 20f. In this case, since a convergent light beam enters the imaging lens, it is sufficient to adjust the focus of the imaging lens to a super-infinite state.

Furthermore, the relationship between the maximum number of stripes on the chart, the number of pixels of the image sensor, the focal length of the test lens, and the focal length of the imaging lens must satisfy the above equation. In other words, this formula is a conditional formula for efficiently resolving the stripes on the chart on the television screen. If the upper limit is exceeded, the maximum number of stripes on the chart will be resolved, but the magnification will be larger than necessary and only a portion of the chart will be visible on the TV screen. Below the lower limit, the maximum number of stripes will be difficult to resolve on the television screen. Furthermore, the angle between the chief ray of the luminous flux emitted from the surrounding chart and the chart surface is θ
When Zhou

0010

[Example 1] Furthermore, when testing the performance of a test lens, it is normal to look at the center and periphery. Therefore, the representative positions of the center and periphery (
Approximately 70% of the image sensor)
(locations) shall be inspected to a minimum. At this time, it is easier to see if the charts on the central and peripheral TV screens have the same size and resolution, so it is better to make the focal lengths of the imaging lenses the same.

[0011] Next, when the inspector inspects the lens by looking at the television monitor, if the performance of the lens to be tested is poor, the chart will not be resolved and there will be a lot of flare. Here, bad conditions can be determined even with a black and white monitor, but if a color monitor is used, the flare will be colored and it will be possible to determine it more accurately.

FIGS. 1 and 2 show the configuration of the apparatus. A is a test lens. 1 is a chart for testing resolution, etc., 2 is a diffusion plate, and 3 is a light source. The light source 3 and the diffuser plate 2 constitute an illumination system. A condenser lens may be provided in place of the diffuser plate 2 to provide a Kohler illumination system.

Reference numeral 4a denotes an imaging lens for image pickup, which receives a back-projection light beam from a chart position on the optical axis of the test lens 4 and forms an image. 4b to 4e are imaging lenses that receive backprojected light beams from off-axis (peripheral) positions of the chart. Further, 5a to 5e are color solid-state image sensors, which sequentially receive images from the imaging lenses 4a to 4e. Reference numerals 6a to 6e are television monitors (television receivers), which are sequentially coupled to image sensors 5a to 5e via a signal processing device (not shown). The imaging lenses have the same focal length, and all the imaging elements are adjusted to equivalent distances from the chart.

Of the light flux from the chart 1 illuminated by the illumination light from the light source 3 via the diffuser plate 2, the position 1 near the optical axis
The light flux from a is converged by the test lens A, and is further imaged onto the image sensor 5a by the imaging lens 4a. The image is then displayed on the television monitor 6a and observed by the examiner.

[0015] Also, the light beams from peripheral positions such as 1b are respectively focused on the image pickup device 5b etc. by the imaging lens 4b etc., and are projected on the screen of the television monitor 4b etc. and observed by the inspector. The image including the image on the monitor 6a is used for the inspector's comprehensive judgment.

FIG. 3 shows another embodiment in which the space taken up is improved by arranging a large number of television cameras or television monitors.

In the figure, parts having the same functions as those in FIG. It is a jig that supports it as much as possible.

Mirrors 8a and 8b are for bending the optical path, and guide the axial inspection light beam to the imaging lens 4a arranged at a position offset from the extension of the optical axis. Mirrors 9a and 9b are also optical path bending mirrors, and mirror 9a in particular is set at an angle suitable for receiving an off-axis backprojection beam. The light beams sequentially reflected by the mirrors 9a and 9b enter the imaging lens 4b. In this example, the projected chart image can only be observed at one peripheral position, but by rotating the test lens A, it is possible to sequentially inspect, for example, the four corners of the imaging screen.

Note that instead of rotating the test lens A, a unit consisting of mirrors 9a and 9b may be rotated, and in that case, the optical axis of the imaging lens 4b is placed on the extension of the optical axis of the test lens A. shall be.

FIG. 4 shows yet another example, in which the test lens B
This is to deal with the case of a variable focus lens.

Although not shown, the imaging lenses 4b to 4d
The angle θ toward the periphery of the chart is changed by a mechanism that moves a lens barrel in which image sensors 5b to 5d are combined in sequence simultaneously and by the same amount along double-headed arrows EP10b to 10d in the radial direction.

Although not shown in the drawings, the operation becomes even more convenient if a mechanism for changing the angle θ in conjunction with the varying operation of the lens B under test is added. Incidentally, it is preferable that the focal length of the imaging lens is also varied in magnification so as to satisfy the above-mentioned formula. FIG. 5 shows a modification of FIG. 4 in which the format of FIG. 3 is replaced.

In addition to the configuration shown in FIG. 3, a swinging mirror 9c is arranged, and this mirror 9c is placed at a position suitable for receiving the back projection light when the test lens B is set at the telephoto end. It shall be locked in position and retracted to the solid line position when not in use.

It is also assumed that the first mirror 9a is provided at a position suitable for receiving the back projection light when the lens B to be tested is set at the wide end.

[0025] At the time of inspection, test lens B or unit 10
shall be rotated.

[0026] If the number of swinging mirrors is increased, inspection can be performed at many angles of view.

As described in the examples above, when inspecting the peripheral performance of a test lens, an imaging lens and an image sensor are provided at each of four locations around the periphery of representative 1, and five locations including the center are simultaneously inspected. There is a method of inspection. In this case, it is sufficient to arrange the five television monitors in an easily viewable position. In addition, the five imaging lenses are placed at a certain distance from the test lens to prevent interference.

[0028] Next, there is also a method in which the lens to be tested is inspected by rotating the test lens by using only one location instead of each of the four locations around the periphery. In other words, you only need to use two TV monitors, one in the center and one on the periphery, but you can watch the periphery in turn at slightly different times. Another method is to inspect the peripheral performance by using two mirrors between the test lens and the imaging lens and rotating the mirrors.

Furthermore, when the lens to be tested is a zoom lens, the imaging lens is also a zoom lens with a focal length range that satisfies the above equation. Next, it is sufficient to prepare as many combinations of mirrors as the number of focal lengths to be inspected, maintain a certain focal length and mirror combination, rotate the mirrors for each, and inspect the performance of the surrounding area.

[0030]

[Effects of the Invention] By using such a device, it is possible to install the device in a normal bright room. Furthermore, the test lens and the television monitor can be placed near the examiner regardless of the focal length of the test lens. Therefore, inspections that could conventionally only be done in a dark room can now be done in a normal bright room, and there is no strain on the eyes of the inspector. Furthermore, the test can be performed by one person regardless of the focal length of the lens to be tested.

[Brief explanation of drawings]

FIG. 1 is an optical cross-sectional view of a first embodiment.

FIG. 2 is a perspective view of the first embodiment.

FIG. 3 is an optical cross-sectional view of the second embodiment.

FIG. 4 is a perspective view of the third embodiment.

FIG. 5 is an optical cross-sectional view of the fourth embodiment.

[Explanation of symbols]

A/B Test lens 1 Chart 4a-4e Imaging lens 5a-5e Solid-state image sensor 6a-6e TV monitor

Claims (6)

[Claims] 1. A test chart disposed on the image plane side of a test lens, an illumination means for illuminating the chart, a television imaging means for imaging the axial position of the chart through the test lens, and the television imaging system. Lens inspection characterized by comprising: a television imaging means having an optical path inclined with respect to the optical path of the means and for imaging an off-axis position of the chart; and a television monitor for observing the output image of each television imaging means. Device. 2. A claim characterized in that the optical path of the television imaging means for imaging the off-axis position of the chart can change the inclination angle with respect to the optical path of the television imaging means for imaging the on-axis position of the chart. 1 lens inspection device. 3. The lens inspection apparatus according to claim 1, wherein each television imaging means is for color imaging. 4. A chart is placed on the image plane side of the test lens, the chart is illuminated and the back-projected light beam is formed into an image using an imaging lens, an image sensor is placed on this image formation plane, and the image is captured. This is a device for observing the chart image on the element on a TV monitor, and the imaging position of the back-projected light beam is from infinity to 20f (f
:focal length of the test lens), the maximum number of stripes to be inspected on the chart (black and white are counted as 1 per 1 mm) is N, the number of pixels per 1 mm of the image sensor is M, When the focal length of the imaging lens is F, 3(2
It satisfies the relationship of A lens inspection device characterized by inspecting performance. 5. The lens inspection apparatus according to claim 4, wherein the focal length of the imaging lens with respect to the chart at the center of the optical axis and the focal length of the imaging lens with respect to the peripheral charts are the same. 6. The lens inspection apparatus according to claim 4, wherein the image pickup device and the television monitor are color compatible.