JPS61170635A - Method and instrument for measuring optical flare - Google Patents

Abstract

PURPOSE:To enable exact flare measurement even in optical measurement in which a target cannot be made in the case of visible light like in a UV or IR optical system by constituting a titled instrument in such a manner as to measure the flare by using a spot light source. CONSTITUTION:The light from a spot light source 21 passes through an optical system 25 to be measured and forms the spot image distribution of the spot light source on the video plane 26 thereof. The video plane thereof is vertically and horizontally scanned two-dimensionally by a point detector 27 and the function G (x, y) of the spot image intensity distribution 26a on the video plane is measured. The light signal within the size of the detector 27 is integrated by the detector itself and therefore the measurement is executed by the two-dimensional scanning at the pitch of the point detector size. The total integrated value of the spot image intensity is determined and the flare quantity of the optical system to be measured is determined from the ratio between the remaining part after subtracting the part corresponding to the dark black part from the total integrated value and the total integrated value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for measuring flare (also referred to as Bering glare) of an optical system (visible light or non-visible light).

(Prior Art) Flare is a cause of poor image contrast due to light scattering by lens elements in the optical system, and is an important evaluation element along with resolution in the optical systems of night vision devices and infrared devices.

Conventionally, this type of optical system flare measurement method and device include:
The configuration shown in FIG. 3 regarding a visible optical system is known. In FIG. 3, 1 is a screen;
A dark area 2 is provided above. 3 is a lighting device that uniformly illuminates the screen 1, and 5 is an optical system to be measured. The target of the optical system to be measured M5 is the screen 1 having the dark portion 2, 6 is the image plane of the optical system to be measured, and 6a is the image plane signal intensity distribution representing the measured light intensity of the image plane.

Here, a conventional flare measuring method shown in FIG. 3 used in a visible optical system will be explained.

A dark area 2 formed by a hole or the like in which no light is reflected is provided in a screen 1 that is sufficiently larger than the field of view of the optical system 5 to be measured, and this screen 1 is uniformly illuminated. This screen 1 is observed by an optical system to be measured 5, and the light intensity of the image plane 6 is measured. At that time, the signal intensity ratio I (b)/I (o) between the dark part I (b) and the bright part I (o) corresponding to the screen image of the image plane signal intensity distribution 6a representing the light intensity on the image plane is given. Let it be the flare of the optical system to be measured.

(Problems to be Solved by the Invention) By the way, conventional flare measurement devices are configured with a visible optical system, and therefore use a large screen as a target for the optical system to be measured. In this case, such a light source cannot be manufactured. Even if we were to create an extraordinary heat panel and provide a dark area within it, this dark area would have to be at absolute zero (-273 degrees Celsius), making such a target impossible to achieve.

(Means for Solving the Problems) The present invention was made to eliminate the above-mentioned conventional drawbacks, and uses a point light source as a target to The integral value of the point spread intensity distribution on the image plane imaged by By measuring the ratio between the area and the integral value, it is possible to perform the same measurements as conventional measurements, and it is also possible to accurately measure flare even in optical measurements where targets cannot be created, such as in the case of visible light such as infrared optical systems. The present invention aims to provide a method and apparatus for measuring optical system flare.

First, a detailed explanation of the present invention will be given with reference to FIG. In this figure, 21 is a point light source as a target, 25 is an optical system to be measured, 26 is an image plane of the optical system to be measured, 27 is a point detector, and 26a is a point light source that serves as a target.
This is a point spread intensity distribution measured in two dimensions. Although the screen 1 and the dark area 2 shown by dotted lines are unnecessary in the measurement of the present invention, they represent the screen used in the conventional configuration of FIG. 3 and the position of its dark area.

Now, the light (visible light or non-visible light such as infrared rays and ultraviolet rays) from the point light source 21 passes through the optical system 25 to be measured, and the image plane 2
6. Create the point spread distribution of the point light source. The image plane is scanned two-dimensionally in the vertical and horizontal directions by the point detector 27, and the function G(x, y) of the point spread intensity distribution 26a on the image plane is measured. At this time, since the optical signal within the size of the point detector 27 is integrated by the detector itself, measurement is performed by two-dimensional scanning at a pitch of the point detector size. Since the surface light source (illuminated screen) used in the conventional case shown in FIG. Now, as shown in equation (1), calculate the total integral value of the point spread intensity, subtract the part corresponding to the dark area (width d in Figure 1) from the total integral value, and calculate the remaining part (Figure 1). (new line part) and the total integral value. However, the value of the width d is usually selected to be approximately 1 to 2 degrees of the visual angle of the optical system.

(Example) Next, the configuration of an example of the present invention will be described with reference to FIG. In FIG. 2, infrared rays from a point light source 31 are made into intermittent light by a chip 32 that interrupts infrared rays, and then the light source is defined to the required size (so that it becomes a sufficiently small point). The light is emitted from the aperture 33 through an optical filter 34.

The infrared rays that have passed through the optical system 35 to be measured create a point spread distribution on the optical system image plane 36. The infrared detector 37 is connected to the controller 38
It is provided on an XY fine movement stage 39 that automatically performs two-dimensional scanning in the x and y directions, and scans the image plane to measure the point spread intensity distribution. At this time, the scanning pitch is set to the size of the infrared detector. This measurement signal is input to the lock-in amplifier 40. The lock-in amplifier 40 receives the synchronization signal S from the chopper 32 and performs an amplification operation only during the period when infrared rays are passing through the chopper 32. The output of the lock-in amplifier 40 is further amplified by a log amplifier (logarithmic amplifier) 41, then converted to a digital signal by an AD converter 42, and integrated in calculation 8!43. The calculator 43 calculates the amount of flare based on the above-mentioned equation (1), and displays it on a display device 44 such as a printer or plotter.

In the above embodiment, the case of measuring flare of an infrared optical system was exemplified, but it is clear that the present invention is capable of measuring flare of not only an infrared optical system but also an ultraviolet or visible light optical system. .

(Effects of the Invention) As explained above, according to the present invention, flares are measured using a point light source, which makes it easy to use ultraviolet and infrared optical systems that could not be achieved with conventional configurations. This method has the advantage of being able to be easily measured using a conventional method, and also provides high measurement accuracy. Furthermore, since the target is a point light source, it is easy to manufacture, and even when applied to the measurement of visible light, the device can be made inexpensive and compact.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of optical flare measurement according to the present invention, Figure 2
The figure is a block diagram showing an embodiment of the optical system flare measurement apparatus of the present invention, and FIG. 3 is a diagram showing the principle of conventional optical system flare measurement. 1...Screen, 2...Dark area, 3...Illuminating device, 5.25.35...Optical system to be measured, 6, 26 3
6... Image plane, 6a... Image plane signal intensity distribution, 21.
31... Point light source, 26a... Point spread intensity distribution, 27.
37...Detector, 32...Chopper, 33...
Aperture, 34... Optical filter, 38... Controller, 39... XY fine movement stage, 40...
Lock-in amplifier, 41...Log amplifier, 42...
AD converter, 43...computer, 44...display device.

Claims (2)

[Claims] (1) Using a point light source as a target, find the integral value of the point image intensity distribution imaged by the optical system to be measured, and subtract the part corresponding to the dark area in the surface light source from the integral value, and then calculate the remaining part. , a method for measuring flare in an optical system, characterized in that the amount of flare of the optical system to be measured is determined by a ratio to the integral value. (2) A point light source, a chopper that cuts off the light from the point light source, and a point image intensity distribution on the optical system image plane caused by the light that has passed through the optical system to be measured is measured by scanning the optical system image plane. comprising a detector and an amplification calculation means having a lock-in amplifier for amplifying a measurement signal of the detector in synchronization with the operation of the chopper, and calculating an integral value of the point spread intensity distribution by the amplification calculation means; An apparatus for measuring flare in an optical system, characterized in that the ratio of the integral value to the remaining portion after subtracting a portion corresponding to a dark area in a surface light source from the integral value is calculated.