JP3019431B2 - OTF measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line spread function (L) of an optical system by scanning a slit pattern.
The present invention relates to a device for measuring an optical transfer function by taking an SF).

[0002]

2. Description of the Related Art An optical transfer function (O) is used as a scale for unifying and quantitatively evaluating the imaging characteristics of various optical systems and optical devices.
A quantity called a ptical transfer function (OTF), a modulation transfer function (MTF), or a phase transfer function (PTF) is used. This is because, for an object with a spatial periodic structure, when considering the spatial frequency ν, which is the reciprocal of the period, as an amount representing the fineness, the images of the periodic structure with various spatial frequencies ν are generated by a certain optical system. This is a quantitative representation of what contrast is reproduced.

Conventional devices for measuring OTF, MTF, etc.
The intensity distribution of the image formed by the test optical system is scanned by any method, and OTF, M
Obtaining TF and the like is the principle of measurement. Generally, the test optical system to be measured by the present measuring apparatus is a single lens or a combination of single lenses, or a combination of a lens, a mirror, a prism, and the like.

The OTF is defined as the Fourier transform of the intensity distribution of a point image or a line image. However, since measuring the intensity distribution of a point image is disadvantageous in terms of securing a necessary light amount, the OTF is determined based on the linear distribution of the intensity distribution of the line image. Measurements for the original OTF are mainly performed. In this case, the light diverging from the narrow slit is imaged by the lens to be detected, and the intensity distribution of the image is converted into an electric signal in a scanning unit in which the light receiving device and the scanning mechanism are combined. FIG. 4 is a schematic view of a main part of a conventional OTF measuring device.

In FIG. 4, reference numeral 4 denotes a light source, reference numeral 5 denotes an illumination optical system, and reference numeral 1 denotes an optical system to be detected. The photoelectric detection means 7 detects an image on the test pattern plate 3.
The scanning of the line image is performed by a slit opening provided in the test pattern plate 3. To scan an image,
As shown here, if the light-receiving plate 8 is fixed and the image moves on the slit-shaped opening of the light-receiving plate 8, or if the slit-shaped opening of the light-receiving plate 8 moves with respect to the fixed image. Good.

[0006] Since the electric signal obtained by the slit scanning is the intensity distribution itself of a line image, the OTF is obtained by performing an analog or digital Fourier transform on this. The output of the photodetector obtained when scanning with a grating instead of a slit contains an electrical frequency component corresponding to the spatial frequency determined by the pattern of the grating, and a signal of a certain frequency has a value corresponding to the MTF. And the phase is P
Give the value of TF itself. Furthermore, if scanning is performed while changing the grating interval one after another, and a spatial frequency component determined by the grating interval is electrically extracted, the OTF can be measured.

In order to measure the OTF in an optical system having an angle of view, the OTF is measured in both the meridional direction (hereinafter abbreviated as the m direction) and the sagittal direction (hereinafter abbreviated as the s direction). Must. FIG. 5A is a diagram showing a state of the apparatus when measuring the OTF in the m direction.

At this time, after the slit opening is positioned in the m direction, scanning is performed in the direction indicated by D. Next, when measuring in the s direction, the slit opening is aligned in the s direction, and scanning is performed in the direction indicated by E in FIG. 5B. As can be seen from the figure, in the conventional apparatus, in order to measure the OTF in both the m and s directions, it is necessary to rotate the entire scanning mechanism including the test pattern plate 3 by 90 ° around the optical axis (indicated by F in the figure). there were.

[0009]

That is, the conventional OT
In the F-measuring device, a rotating mechanism must be provided in the scanning operation part. Since the rotation accuracy (including reproducibility) of the test pattern plate is a major cause of errors in the measurement results, the rotation positioning accuracy must be strict to achieve accurate measurement. In general, it is technically difficult to provide a rotating mechanism with higher precision to a structure that performs a scanning operation, so that the apparatus must be enlarged and complicated. In this respect, not only the accuracy but also the cost has been a problem that requires improvement in manufacturing the device.

The present invention has been made in view of such conventional problems, and provides an OTF measuring apparatus which enables accurate measurement in both the m and s directions by a simple method that does not require a complicated rotating mechanism. The purpose is to do.

[0011]

According to a first aspect of the present invention, there is provided an OTF measuring apparatus for projecting a predetermined pattern formed on a test pattern plate through an optical system to be inspected, and the intensity distribution of the projected image. The OTF is measured by photoelectrically detecting the OTF, wherein the test pattern plate has at least one pair of slit patterns forming an angle of 90 ° with each other, and the test pattern plate has an angle of 45 ° with respect to the slit pattern. The above problem is solved by providing a scanning means for moving the test pattern plate in an angled direction.

According to a second aspect of the present invention, an OTF measuring device projects a predetermined pattern formed on a test pattern plate via an optical system to be detected, and photoelectrically detects an intensity distribution of the projected image. To measure the OTF,
The photoelectric means may be at least one at an angle of 90 ° to each other.
By having a light receiving plate having a pair of slit-shaped openings, and having scanning means for moving the light-receiving plate in a direction at an angle of 45 ° with respect to the pair of slit-shaped openings,
The above problem has been solved.

The "test pattern plate" referred to in the claims means a member provided with a test pattern such as a slit, a pinhole, a knife edge, or a lattice, which is a subject of the optical system to be measured.

[0014]

According to the present invention, a test pattern plate for scanning a line image or a light receiving plate has at least one pair of slit patterns forming an angle of 90 ° with each other, and the OTF measurement when there is an angle of view is performed. Scanning is performed by setting a dedicated slit in each of the m direction and the s direction at a desired position. At this time, since the scanning means for moving the test pattern plate in a direction forming an angle of 45 ° with respect to the slit pattern is provided, the test pattern plate or the light receiving plate can be continuously measured in both directions. The OTF in both the m and s directions can be measured only by scanning in one direction without requiring a rotation operation.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a schematic diagram showing an OTF measuring apparatus according to a first embodiment of the present invention.

Reference numeral 1 denotes a test lens as a test optical system of the present embodiment. In this embodiment, a single lens is used as the optical system to be tested. However, the present apparatus is applicable to an optical system configured by combining a single lens or a combination of a lens, a mirror, and a prism. It goes without saying that it is applicable.

The test target unit 2 has a test pattern plate 13 to be an object of the optical system to be inspected, and is set on one conjugate image side of the lens to be inspected. The test target unit includes a light source 4 and an illumination optical system 5, a filter 6 for selecting a wavelength of measurement light, a diffusion plate (not shown), a relay optical system (not shown), and the like. In this embodiment, a thin slit is used as a test pattern. Alternatively, a periodic pattern such as a knife edge, line and space, or the like can be used.

Numeral 10 denotes a collimator lens for forming a parallel light beam incident on the lens to be measured when measuring the OTF of the lens to be measured at an object position at infinity.
Reference numeral 11 denotes a relay lens as an additional optical system used to relay and form an image having a size suitable for measurement on the opening of the light receiving plate 8.

The light receiving section 7 is the photoelectric detecting means of the present embodiment, and is a section for converting the light intensity distribution of the image of the test target formed by the test lens 1 into an electric signal. The components of the light receiving section are a condensing optical system (not shown) and a light receiver (not shown)
And so on. Note that the condensing optical system is used to make all light entering the aperture enter the light receiving device.

An output signal generated by the light receiver is sent to a signal processing system (an analog circuit, a digital circuit, or an electric circuit obtained by mixing them). In the signal processing system 12,
The output signal is processed and OTF, MTF, PTF
Is obtained, and an electric signal to be supplied to a display and recording device (not shown) is created from this signal.

On the test pattern plate 13, a pair of test patterns, ie, an m-direction slit B and an s-direction slit A, form an angle of 90 ° and an angle of 45 ° with respect to the scanning direction C. Are arranged as follows.

Next, the operation of this embodiment will be described with reference to FIG. First, the image of the test target formed by the test lens 1 is observed by an observation optical system (not shown), and the scanning aperture is positioned. At the time of measurement in the m direction, the slit B is adjusted to a desired position as shown in FIG. 2A, and then scanning is performed in the C direction by the scanning means. As a result, the slit image runs laterally on the light receiving plate 8, and a line spread function (LSF) of the lens 1 to be measured can be obtained.
The OTF in the m direction can be measured.

When measuring in the s direction, the slit A is adjusted to a desired position as shown in FIG. 2B, and then scanning is performed in the C direction in the same manner as in the m direction. As a result, the slit image runs vertically on the light receiving plate 8, so that the OTF measurement in the s direction can be performed. In the present embodiment, the light receiving plate 8 changes the direction of the slit opening of the light receiving plate in the same plane, and the slit A
Has an adjustment mechanism for matching the direction.

(Second Embodiment) FIG. 3 is a schematic view showing an OTF measuring apparatus according to a second embodiment of the present invention. OT of this embodiment
In the F measuring device, the scanning of the line image described above is performed by the light receiving device 9.
This is different from that of the first embodiment in that the light receiving plate 18 provided before is moved. For this reason, in the present embodiment, a pair of slit-shaped openings are provided in the light receiving plate 18.

Here, at the time of measurement in the m direction, the slit B is adjusted to a desired position as in the first embodiment, and thereafter scanning is performed in the C direction by the scanning means. As a result, the slit image runs laterally on the light receiver, the LSF of the lens 1 to be measured can be obtained, and the OTF in the m direction can be measured.

In the case of the s direction, the slit A is adjusted to a desired position, and then scanning is performed in the C direction in the same manner as in the m direction.
As a result, the slit image runs vertically on the light receiver, so that the OTF measurement in the s direction can be performed.

Here, the measuring apparatus of the second embodiment has an adjusting mechanism for changing the direction of the slit of the test pattern plate 3 in the same plane so as to match the direction of the slit-shaped opening of the light receiving plate 18. are doing. When the test pattern provided on the test pattern plate 3 is not a slit but a pinhole, a mechanism for rotating the test pattern plate is not required.

In the first and second embodiments, when it is necessary to measure the OTF in a certain direction (other than the m and s directions), a slit having an appropriate angle is formed in the test pattern plate or the slit. What is necessary is just to provide in a light-receiving plate. Further, in such a case, it is equally effective to provide not only slits but also line and space periodic patterns in various directions.

[0029]

As described above, according to the present invention, the OTF measurement in both the m and s directions can be performed without rotating the structure having the scanning mechanism around the optical axis. The measurement error caused by the positioning error of the above is released. In addition, since the positioning operation by rotation can be omitted, it contributes to the reduction of the measurement time. Furthermore, since the measuring device can be simplified, the device can be easily manufactured, and a more precise device can be used, so that the accuracy of the measurement is further improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of an OTF measuring apparatus according to a first embodiment of the present invention.

FIGS. 2A and 2B are explanatory diagrams showing the operation of the OTF measuring device according to the first embodiment of the present invention.

FIG. 3 is a perspective view of an OTF measuring apparatus according to a second embodiment of the present invention.

FIG. 4 is a perspective view of an OTF measuring device according to a conventional method.

FIGS. 5 (a) and 5 (b) are explanatory diagrams showing the operation of the OTF measuring device according to the conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test lens 2 Test target part 3, 13 Test pattern board 4 Light source 5 Illumination optical system 6 Filter 7 Light receiving part 8, 18 Light receiving plate 10 Collimator lens 11 Relay optical system As S direction measurement slit B m direction measurement slit C Scanning direction D Scanning direction when measuring in the m direction E Scanning direction when measuring in the s direction

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01M 11/00-11/02 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A test pattern formed on a test pattern plate is projected through an optical system to be inspected, and the OTF of the optical system to be inspected is detected by photoelectric detection means for photoelectrically detecting the intensity distribution of the projected image. In an OTF measuring apparatus for measurement, the test pattern plate has at least one pair of slit-shaped openings forming an angle of 90 ° with each other, and forms an angle of 45 ° with the pair of slit-shaped openings. An OTF measuring device comprising scanning means for moving a test pattern plate in a direction. 2. A test pattern formed on a test pattern plate is projected through a test optical system, and the OTF of the test optical system is detected by photoelectric detection means for photoelectrically detecting the intensity distribution of the projected image. In the OTF measuring apparatus for measuring, the photoelectric detecting means is at least one angle of 90 ° with each other.
An OTF comprising: a light receiving plate having a pair of slit-shaped openings; and scanning means for moving the light receiving plate in a direction forming an angle of 45 ° with respect to the pair of slit-shaped openings. measuring device.