JPH02236432A - Method and device for measuring specific image surface illuminance of lens - Google Patents

Abstract

PURPOSE:To easily perform measurement of even an arbitrary measuring line in a short time by picking up the image of a reference lens having a known specific image surface illuminance by an image pickup means to obtain measured data. CONSTITUTION:The image of a surface illuminant is picked up through the reference lens having a known specific image surface illuminance by the image pickup means. This means is provided with many pixels arranged in a matrix, and the light made incident on each pixel is converted to an electric signal. Electric signals photoelectrically converted by these pixels are read out and are used as reference measured data. The image of the surface illuminant is picked up through a lens to be examined by the image pickup means to generate measured data. A ratio of obtained measured data to reference measured data is multiplied by the specific image surface illuminance of the reference lens to calculate the specific image surface illuminance of the lens to be examined. This operation is performed for picture elements on a designated measuring line, and the specific image surface illuminance is calculated for each picture element. The calculated specific image surface illuminance is displayed on a display means or printed out by a printer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method and apparatus for measuring specific image plane illuminance of a lens.

[Conventional technology]

Specific image plane illuminance (peripheral illuminance ratio) is used as one of the performance evaluations of lenses, and this is expressed by the horizontal axis representing half-hundred angles (ω/2) and the dark blue axis representing the ratio of the paraxial specific image surface illuminance (ω/2). %) is expressed as a graph. It is widely known that the CQS' law holds true for this specific image plane illuminance when there is no distortion, and the illuminance decreases in the periphery of the image plane.

Conventional measurements of specific image plane illuminance use a photometer with a bin hole placed in front of the photomultiplier, and this photometer is moved over the image plane of the lens to be tested to measure light from the diffuser plate illuminated by a lamp. The light is measured. Next, the ratio of the illuminance at each point on the image plane to the paraxial illuminance is determined and plotted to create a specific image plane illuminance curve.

[Problems to be Solved by the Invention] In the conventional method for measuring the specific image plane illuminance described above, the photometry unit must be moved on the image plane, which makes the measurement time-consuming and the measuring device complicated. There are drawbacks.

In particular, multiple measurement lines passing through the paraxial direction, e.g. in the meditorial direction. This problem becomes serious when measuring lines in the +digital direction and diagonal directions as well.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for measuring specific image plane illuminance of a lens, which is simple and quick, and allows measurement of any measurement line.

[Means for Solving the Problems] In order to achieve the above object, the measurement method of the present invention uses an imaging means to image a surface light source with uniform luminance through a reference lens with a known specific image plane illuminance, and Create reference measurement data from the output signal of the means, image the surface light source through a test lens whose specific image plane illuminance is unknown to create measurement data, and combine this measurement data with the specific image plane illuminance of the reference lens and The specific image plane illuminance of the lens to be tested is determined from the reference measurement data.

The measurement device of the present invention incorporates a surface light source with uniform luminance and an imaging means for capturing an image of the surface light source, and a reference lens with a known specific image surface illuminance and a test lens with an unknown specific image surface illuminance. Standard measurement data created from the output signal of the imaging means when the surface light source is imaged through the reference lens, measurement data created by imaging the surface light source through the test lens, and the standard. calculation means for calculating the specific image plane illuminance of the test lens using the specific image plane illuminance of the lens;
and display means for displaying the specific image plane illuminance of the lens to be tested calculated by the calculation means.

[Operation] First, as a preparatory work, a surface light source is imaged by an imaging means through a reference lens whose specific image plane illuminance is known. This imaging means includes a large number of vixels arranged in a matrix, and converts light incident on each pixel into an electrical signal. The electrical signals photoelectrically converted by these vixels are read out and used as reference measurement data. Next, the surface light source is imaged by the imaging means through the lens to be tested, and measurement data is created. The ratio of the obtained reference measurement data and measurement data is multiplied by the specific image plane illuminance of the reference lens to calculate the specific image plane illuminance of the test lens. This calculation is performed for pixels on the specified measurement line, and the specific image plane illuminance is calculated for each pixel. The calculated specific image plane width is displayed on a display means or printed out with a printer.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

The frame memory 2 stores light emission data, and the light emission data read out from the frame memory 2 is converted into an analog signal by the D/A converter 3 and then sent to the driver 8. This driver 8 drives the CRT 5 to uniformly emit light from its light emitting surface 5a. Instead of this CRT50,
A surface light source consisting of a lamp and a diffuser plate may also be used.

The TV camera 7 has a built-in CCD type or MOS type imaging device, and a reference lens 9. The lens to be tested 10 is attached replaceably. Optical lens systems 9a and 10a are attached to these reference lens 9 and test lens 10.

The video signal output from the TV camera 7 is A/D
After being converted into a digital signal by the converter 12, the memory 1
3 or written to memory ■4.

In addition, the synchronization signal output from the TV camera 7 is sent to the CPU
16. It is sent to address decoder 17 and A/D converter l2. The CPU 16 uses the memory 13.1 based on the synchronization signal.
The address decoder l7 also specifies the address of the memory 13.14. selector l8
is connected to the address decoder 17 side when writing to the memory 13, 14, and connected to the CPU 16 side when reading from the memory 13, 14.

The CRT display device 19 displays not only the calculated specific image plane illuminance data but also the measurement procedure and the like. In addition,
Reference numeral 20 is a keyboard, reference numeral 21 is a RAM, and reference numeral 22 is a ROM.

Next, the operation of the above embodiment will be explained. First, operate the keyboard 20 to select a diskette device (not shown).
Data on the specific image plane illuminance of the reference lens 9 is read from , and written into the RAM 21 .

Next, the CRT 5 is turned on and the light emitting surface 5a is caused to emit light with uniform brightness using the light emitting data read from the frame memory 2.

When the keyboard 20 is operated to instruct measurement of the reference lens 9, the selector l8 is switched to the address decoder 17 side. The TV camera 7 images the light emitting surface 5a, outputs a video signal, and sends this to the A/D converter 12. This A/
Since the D converter 12 performs sampling in synchronization with the reading of the video signal, the output signal of each pixel is digitally converted.

This digital signal is sent to the memory 12 and written to the address specified by the address decoder 17. Therefore, reference measurement data for l frames captured through the reference lens 9 is written into the memory 13.

After measuring the reference lens 9, the test lens 1.0 is placed on the TV camera 7, and then the keyboard 20 is operated to instruct measurement of the test lens IO. In this case, memory 1
4 enters the write mode, one frame of reference data captured through the lens 10 to be tested is written into the memory 14.

After measuring the lens 10 to be tested, the keyboard 20 is operated to instruct calculation of the specific image plane illuminance of the lens 10 to be tested. cpu
ta switches the selector 18 to the CPUI 6 side and reads out the measurement data of the pixels on the measurement line 30 shown in FIG. 2 from among the reference measurement data stored in the memory 13. Furthermore, the CPU 16 reads the measurement data of the lens 10 to be tested from the memory l4, and calculates the ratio of the same pixels.

By multiplying the obtained ratio of each pixel by the specific image plane illuminance of the reference lens 9 read from the RAM 21, the specific image plane illuminance on the line 30 is determined. The calculated specific image plane illuminance curve is displayed on the CRT display device 19 by operating the keyboard 20. Note that by using a mouse or the like, it is possible to obtain the specific image plane illuminance for the measurement line 31 shown by the dotted line and the measurement line 32 shown by the dashed-dotted line. Here, FIG. 2 shows the imaging surface of the imaging device 8. As shown in FIG.

When measuring another lens to be tested, since the measurement of the reference lens 9 has already been completed, it is sufficient to attach this lens to the TV camera 7 and take an image of the CRT 5 as described above.

Next, calculation of the specific image plane illuminance will be explained with reference to FIG. The reference lens 9 has a specific image plane illuminance as shown in (A), and the specific image plane illuminance at the half angle of view ωl is rH,
Suppose that Moreover, the measurement data of the reference lens 9 is (
Assume that it is "I" as shown in B). When the test lens 10 is measured under the same conditions, if the measurement data is "J", the specific image plane illuminance "K" at the half angle of view ω1 of the test lens 10 can be obtained from the following formula. ,ru. Here, "■.

J, "JOJ are the reference lens 9 and the test lens 1, respectively.
This is measurement data on the optical axis of 0.

In the embodiment described above, a CRT is used as a surface light source, but instead, for example, a diffuser plate may be illuminated with a lamp.

〔Effect of the invention〕

As described in detail above, according to the present invention, measurement data is obtained by imaging a reference lens whose specific image plane illuminance is known using an imaging means, and a test lens is imaged with the same imaging means, Since the specific image plane illuminance of the test lens is calculated from the obtained iUII constant data, the measurement data of the reference lens, and the specific image plane illuminance, it is possible to use a simpler measurement device and take a shorter time than the conventional measurement method. The specific image plane illuminance can be measured with

In addition, since the ratio of the measurement data of the reference lens and the test lens is used, even if there are variations in the brightness of each pixel of the imaging means, accurate illuminance measurement can be performed without being affected by this. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the measurement equipment of the present invention. FIG. 2 is an explanatory diagram showing measurement lines. FIG. 3 is a graph showing the specific image plane illuminance and measurement data of the base lens and the test lens, respectively. 5 ・ ・ ・ ・ CRT 5a...Light emitting surface 7...TV camera 8...Imaging device 9...Reference lens 10...Test lenses 30 to 32...Measurement line.

Claims (2)

[Claims] (1) Use an imaging device to image a surface light source with uniform luminance through a reference lens with a known specific image plane illuminance, and create reference measurement data from the output signal of this imaging device. Measurement data is created by imaging the surface light source through the test lens, and the specific image surface illuminance of the test lens is determined from this measurement data, the specific image surface illuminance of the reference lens, and the reference measurement data. A specific image plane illuminance measurement method. (2) Built-in surface light source with uniform luminance and imaging means for capturing an image of this surface light source, allowing interchangeability between a reference lens with known specific image surface illuminance and a test lens with unknown specific image surface illuminance. The comparison between the attached television camera, the reference measurement data created from the output signal of the imaging means when imaging the surface light source through the reference lens, the measurement data created by imaging the surface light source through the test lens, and the reference lens. and a display means for displaying the specific image plane illuminance of the test lens calculated by the calculation means. Illuminance measurement device.