JPH06123675A - Measuring method of pupil decentering eccentricity ratio of optical system - Google Patents

Abstract

PURPOSE:To easily measure a pupil decentring eccentricity ratio in conjunction with the image deterioration due to the decentering eccentricity. CONSTITUTION:Four point images of light spot on a reference light axis by an optical system to be detected is formed on an image face 6 of a relay lens 4 having a pupil-four-divided prism 5 provided in the vicinity of an emitting pupil. On the basis of an area or each center intensity of each binary coded image in identical levels of four point images, a pupil decentering eccentric ratio is calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system eccentricity measurement, and more particularly to a method for measuring a pupil eccentricity.

[0002]

2. Description of the Related Art As an assembled eccentricity measuring technique, the eccentricity of each optical surface is measured by an autocollimation method. Japanese Unexamined Patent Publication No. 61-48742 discloses a conventional eccentricity measuring method using this autocollimation method. In this method, a thin laser beam is applied to a lens to be inspected through a plane-parallel plate, and the plane-parallel plate is rotated so that the laser beam is scanned in parallel to detect the azimuth of the reflected beam from each surface. By doing so, the amount of eccentricity on the entire surface is measured at once.

[0003]

When measuring the amount of eccentricity of each optical surface, the eccentricity allowable amount of each optical surface is clarified based on the quality standard of the optical system as a premise. Need to be. Moreover, these allowable eccentricity values are often set by ray tracing, evaluation simulation, or the like. However, the allowable amount of eccentricity set by such a method is generally a stricter value than the actual allowable amount. The reason is that the image evaluation is determined by a direct relationship with the amount of eccentricity. From the above, in the above-mentioned conventional technique, there is a problem that the eccentricity amount of a stricter tolerance than necessary is measured.

The present invention has been made in consideration of the above circumstances, and based on the allowable amount of the pupil eccentricity after clarifying the relationship between the pupil eccentricity existing in the optical system and the image evaluation by simulation. , A pupil eccentricity measuring method for measuring and evaluating the pupil eccentricity of an optical system.

[0005]

Generally, the quality of an image formed by an optical system depends on the magnitude of pupil aberration of the optical system. The magnitude of this pupil aberration increases as the pupil eccentricity obtained by dividing the pupil eccentricity by the pupil radius increases. Therefore, according to the present invention, a relay lens having a pupil four-division prism arranged near the exit pupil is used.
The point eccentricity is measured by forming the point images, and using the area of the binarized image or the central intensity of each of the four point images at the same level.

[0006]

EXAMPLE 1 FIG. 1 shows the structure of a measuring system to which Example 1 of the present invention is applied. In the figure, 1 is a pinhole, 2 is a lens to be inspected, and 3 is a measuring optical system. The measurement optical system 3 is composed of a pupil 4-division prism 5, a relay lens 4, and a television camera 6. FIG. 2 shows a pupil four-division prism 5 in the measurement optical system 3, and 5a and 5c have the same wedge prism,
5b and 5d are the same wedge prism. The pupil four-division prism 5 is formed by side-bonding these four wedge prisms.

The elements described above are coaxially arranged, the pinhole 1 is arranged at the reference object point position of the lens 2 to be inspected, and the television camera 6 is arranged at the reference secondary point image position of the pinhole 1. Will be placed. Further, the pupil four-division prism 5 is arranged at the exit pupil position of the relay lens 4.

In the above construction, the point image of the pinhole 1 is formed near the reference image point 7 of the lens 2 to be inspected by the lens 2 to be inspected, and this is divided by the relay lens 4 and the pupil 4-splitting prism 5 at the exit pupil. 4 identical point images 9
They are formed on the television camera 6 as a, 9b, 9c and 9d (see FIG. 3). On the other hand, the pupil 4-division prism 5
In the case where the pupil eccentricity as shown in FIG. 4 exists, the same point images as shown in FIG. 3 are not obtained, but four point images having different sizes are obtained as shown in FIG. In FIG. 4, 8 is a circle indicating the size of the pupil, and the coordinates of its center O are (X,
Y). Then, each of the four regions divided by the division lines X-axis and Y-axis (the origin is on the optical axis) of the pupil 4-division prism 5 placed on the exit pupil plane is 8
a, 8b, 8c, 8d. 5 and 6, binarized images obtained by binarizing four point images on the television camera 6 formed by these four light beams at 100% are 9a, 9b, 9c, and 9d. . Intensity distributions 10a, 10b, 1 of these point images 9a, 9b, 9c, 9d
By regarding 0c and 10d as Gaussian distributions having the same k value, the intensity distribution can be obtained by Equation 1. In Expression 1, n is 1, 2, 3, 4.

[0009]

[Equation 1]

9a, 9b when binarized with Zn = A ₁ ,
The areas corresponding to 9c and 9d are S ₁ , S ₂ , S ₃ and S _{4 respectively.}
Then, these areas are number 2, number 3, number 4,
It becomes number 5.

[0011]

[Equation 2]

[0012]

[Equation 3]

[0013]

[Equation 4]

[0014]

[Equation 5]

Here, since the ratio of the pupil eccentricity amount in the X direction and the Y direction and the pupil radius R corresponds to the pupil eccentricity ratios x and y, the pupil eccentricity ratios x and y are expressed by equations 6 and 7, respectively. Is defined by

[0016]

[Equation 6]

[0017]

[Equation 7]

At this time, if the total amount of light is I, the central intensities A ₁ , A ₂ , A ₃ , and A ₄ of the respective point images are expressed by Eqs.
Equations 10 and 11 are obtained.

[0019]

[Equation 8]

[0020]

[Figure 9]

[0021]

[Equation 10]

[0022]

[Equation 11]

From the above correlations with the equations (2), (3), (4), (5) and (8), (9), (10) and (11), the following equation (12) is obtained.
The approximate expression shown in Expression 13 is obtained.

[0024]

[Equation 12]

[0025]

[Equation 13]

In Equations 12 and 13, k ′ is Equation 14.

[0027]

[Equation 14]

Therefore, x = k ₁ ′ V _x , y = k ₁ ′ V _y
As, the pupil eccentricity in the X and Y directions can be obtained. The pupil eccentricity is theoretically equal to the pupil eccentricity of the lens under test. Here, the value of k ₁ may be experimentally obtained as a device constant. A method of giving the absolute value of the amount of eccentricity as Equation 15 and the direction as Equation 16 is also effective.

[0029]

[Equation 15]

[0030]

[Equation 16]

In such a method, the eccentricity of the pupil can be easily calculated by
Moreover, it is possible to measure with high accuracy.

[0032]

[Embodiment 2] In this embodiment, the pupil four-division prism 5 arranged in Embodiment 1 is moved in the X and Y directions with this position as the origin, and both V _x and V _y values become 0. At this time, the coordinate position of the pupil four-division prism 5 is divided by the design value of the radius of the pupil at the exit pupil position determined by the entire optical system. With this, the pupil eccentricity in the X direction and the Y direction can be obtained. . In such a measurement, the pupil eccentricity can be measured with higher accuracy than in the first embodiment.

[0033]

EXAMPLE 3 In this example, first, the number 8 in the first embodiment, the number 9, number 10, number 11 from number 17, the approximate expression V _'x, V' shown in the equation 18 to calculate a _y.

[0034]

[Equation 17]

[0035]

[Equation 18]

Next, the pupil eccentricities x and y in the X direction and the Y direction are calculated by using these equations 17 and 18, respectively.

[0037]

[Formula 19]

[0038]

[Equation 20]

The pupil eccentricity is calculated by such an approximate expression, but an exact measurement value can be obtained by rigorously solving the expression. Therefore, in this embodiment, the pupil eccentricity can be measured extremely easily.

[0040]

As described above, according to the present invention, the eccentricity of the pupil, which is directly related to the deterioration of the image due to the eccentricity, can be easily and easily measured.

[Brief description of drawings]

FIG. 1 is a side view of a measurement optical system to which the present invention is applied.

FIG. 2 is a perspective view of a pupil four-division prism.

FIG. 3 is a front view of a point image formed by a pupil 4-division prism.

FIG. 4 is a front view of a point image formed by a decentered pupil 4-division prism.

FIG. 5 is a front view of a point image formed by a decentered pupil 4-division prism.

FIG. 6 is a diagram showing a Gaussian distribution for calculating a pupil eccentricity.

[Explanation of symbols]

 1 Pinhole 2 Lens to be inspected 3 Measurement optical system 4 Relay lens 5 Pupil 4-division prism 6 Television camera 7 Reference image point

Claims (1)

[Claims] 1. A light spot on a reference optical axis is determined by an optical system under test.
Of the four point images are formed on the image plane of a relay lens having a pupil four-division prism arranged near the exit pupil, and the area or the center of each of the binarized images at the same level of each of the four point images. A pupil eccentricity measuring method for an optical system, characterized in that the pupil eccentricity is calculated based on intensity.