JPH0755639A - Device and method for measuring focal length of optical system - Google Patents

Abstract

PURPOSE:To measure in an almost actual arrangement the focal length of an optical system which is specified to have finite focal length by providing an arithmetic means for computing the focal length of the optical system to be measured, from the position of the optical system to be measured and from the position of a light-beam convergent- point-detection means. CONSTITUTION:A generating means 1 for a divergent beam of light has a semiconductor laser 2, and an optical support 3 (stand 4 and bench 5) supports an optical system 19 to be measured, in such a manner that the optical system freely moves along its optical axis. The position of the optical system 19 is read by a reader means 6 (laser gage interferometer 7) and stored in a storage means 8. A light-beam convergent-point detection means 9 (two-dimensional CCD sensor 10) detects the convergent point of a beam of light emitted from the optical system 19. An optical support 12 (stand 13 and bench 14) supports the detection means 9 in such a manner that the means 9 freely moves along its optical axis. The position of the detection means 9 is read by a reader means 15 (laser gage interferometer 16) and stored in a storage means 17. An arithmetic means 18 computes the focal length of the optical system 19 from the values stored in the storage means 8, 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for measuring the focal length of an optical system.

[0002]

2. Description of the Related Art As a lens focal length measuring device, FIG.
A configuration shown in FIG. 9 is conventionally known.

The measuring apparatus shown in FIG. 8 is used in a measuring method called a nodal slide method, and includes a light source 51, a reference line 52, a collimator lens 53, a sliding base 54 and a rotary base movable in the optical axis direction. A nodal slide base 56 made of 55 and a microscope 58 installed on an optical bench 57 movable in the optical axis direction are provided. The marked line 52 is arranged at the focal position of the collimator lens 53. The test lens 59 is mounted on the nodal slide table 56.

The nodal slide base is used so that the image of the marked line 52 placed at the focus of the collimator lens 53 does not move even if the test lens 59 is rotated by a small amount in the direction perpendicular to the optical axis by the rotary base 55. 56 slide table 54 and microscope 58
Is adjusted in the optical axis direction, and the position "S" of the microscope 58 at that time is read.

Next, instead of the test lens 59, a glass plate having a marked line is put on a nodal slide table with the direction of the marked line being substantially parallel to the rotation axis of the rotary base 55 and the marked line side facing the microscope 58. The slide table 54 and the microscope 58 are attached so that the image of the glass reference line observed by the microscope 58 does not move even if it is attached to the camera 56 and rotated in the direction perpendicular to the optical axis by the rotary table 55.
Is adjusted along the optical axis. If the position of the microscope 58 at that time is "S ₀ ", the focal length of the test lens 59 is | S-.
It is given by S ₀ |.

The measuring apparatus shown in FIG. 9 is an apparatus used in a measuring method called a magnification method, and includes a light source 60, a reference plate 61 with a known length y, a collimator lens 62 with a known focal length f ₀ , and a microscope. It is equipped with 63.

The standard plate 61 is arranged at the focal position of the collimator lens 62. The test lens 59 is arranged behind the collimator lens 62 with the optical axes aligned with each other.
The image size y ′ of the image of the standard plate 61 generated on the focal plane 64 of 9 is measured by the microscope 63. At that time, the focal length of the test lens is given by (y ′ / y) · f ₀ .

[0008]

The so-called finite specification objective lens used in the optical system for an optical disk, which collects the light beam from the light source directly on the disk surface without passing through the collimator lens, does not require a collimator lens. ,
It is widely used because of its advantages such as a simplified structure and cost reduction. This type of objective lens for optical discs has been mass-produced by injection molding of plastics. In recent years, along with the improvement of injection molding technology for plastics, objective lenses for optical discs have higher precision and higher performance. Came to be desired. Therefore, it is necessary to perform a strict inspection whether the manufactured lens is as designed, and the focal length, which is the most basic geometrical optical characteristic of the optical system, is also an important inspection item.

On the other hand, in the above-mentioned conventionally known focal length measuring method, the nodal slide method and the magnification method, the parallel light flux is imaged by the test lens, and a camera for imaging an object at infinity is formed. Although it can be measured well with a lens or the like, a lens that focuses an object at a finite position, such as an objective lens for use in optical discs with finite specifications, causes a large amount of image blurring due to aberration, and therefore cannot be measured with high accuracy. There was a problem.

[0010]

The present invention has been made to solve the above-mentioned problems, and includes a divergent light beam generating means and an optical support for movably supporting an optical system to be measured in its optical axis direction. A reading means for the position of the optical system to be measured, a storage means for the position read by the reading means, a light flux convergence point detecting means for detecting the convergence point of the light flux emitted from the optical system under measurement, and a light flux convergence point detecting means Is movably supported in the optical axis direction of the light beam emitted from the optical system to be measured, reading means for the position of the detecting means, storage means for the position read by the reading means, and the optical system under measurement. And a calculation means for calculating the focal length of the optical system to be measured from the position of the position b and the position of the light beam convergence point detection means, and a measuring device of the focal length of the optical system.

Further, according to the present invention, the positions of at least three N optical systems to be measured are x _i (i = 1, 2, ...,
N), and the position of the light flux convergence point detection means is y _i (i = 1,
2, ..., N), the calculation means for calculating the focal length is a calculation means for calculating by the formula 3, to provide a measuring device of the focal length of the optical system.

[0012]

[Equation 3]

Further, according to the present invention, the light flux convergence point detecting means is moved to detect the convergence point of the light flux from the optical system to be measured at at least three positions of the optical system to be measured, and the measured points in each of them are measured. There is provided a method for measuring the focal length of an optical system, characterized in that the focal length of the optical system to be measured is obtained from the position of the optical system and the position of the light beam convergence point detection means.

Further, according to the present invention, it is necessary to move the optical system to be measured and obtain the position where the convergence point of the light beam emitted from the optical system to be measured is detected by the light beam convergence point detecting means. Measurement of the focal length of the optical system, which is performed for the position of the output means, and obtains the focal length of the measured optical system from the position of the light beam convergence point detection means and the position of the measured optical system. Provide a way.

Further, according to the present invention, at least three positions x _i (i = 1, 2, ..., N) of the optical system to be measured and positions of the light beam convergence point detecting means are y _i (i = 1, 1. 2, ...,
N) is used to calculate the focal length of the optical system to be measured by the mathematical formula 3, and a method for measuring the focal length of the optical system is provided.

The configuration of the measuring apparatus of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of the measuring apparatus of the present invention.
The measuring apparatus of the present invention comprises a divergent light flux generating means 1 (semiconductor laser 2 in the embodiment) and an optical support 3 (movable table 4 in the embodiment) that movably supports the optical system 19 under measurement. And an optical bench 5), a reading unit 6 (a laser interference length measuring device 7 in the embodiment) for reading the position of the optical system 19 to be measured,
The storage means 8 for the position read by the reading means 6 and the light flux convergence point detection means 9 for detecting the convergence point of the light flux emitted from the measured optical system 19 (in the embodiment, the two-dimensional CCD sensor 1
0) and the light flux converging point detection means 9 movably in the optical axis direction of the light flux emitted from the optical system to be measured 19 (in the embodiment, the stage 13 and the optical bench 1).
4) and the reading means 15 at the position of the light flux convergence point detecting means 9
(Laser interferometer length measuring device 16 in the embodiment) and reading means 1
Storage means 17 for the position read in 5, storage means 8,
And a calculation means 18 for calculating the focal length of the optical system to be measured from the value stored in the storage means 17.

Next, the measuring method of the present invention will be described with reference to FIGS. The measuring method of the present invention comprises the following steps.

After the set number N (≧ 3) of the positions of the optical system 19 to be measured in the optical axis direction is determined, the light beam from the divergent light beam generating means 1 is guided so that its optical axes are substantially coincident with each other. The measurement optical system 19 is installed at the first setting position (step 1).

The light flux converging point detecting means 9 is moved in conformity with the optical axis direction of the light flux emitted from the optical system to be measured to detect the light flux converging point (in the embodiment, the light flux observed as an image by the CCD sensor 10). Is detected as the position where the diameter of the light flux is minimized) (step 2).

[0021] reads the position y ₁ of the position x ₁ and the light beam converging point detecting means 9 of the measurement optical system 19, after storing (step 3), to move the measurement optical system 19 into a second set position ( Step 4).

Hereinafter, steps 2, 3, and 4 are repeated until the set number N of positions of the optical system to be measured 19 is satisfied.

In the N sets of conjugate arrangements thus obtained,
Setting position x _i of the optical system to be measured 19 (i = 1, 2, ...
, N) and the position y _i (i =
1, 2, ..., N), the focal length is calculated using the calculating means 18.

Another measuring method of the present invention will be described.
This will be described with reference to FIGS. 1 and 3. Another measuring method of the present invention comprises the following steps.

After the set number N (≧ 3) of the positions of the light beam convergence point detecting means 9 in the optical axis direction is determined, it is set at the first setting position (step 11).

The measured optical system 19 is moved in the optical axis direction,
The position of the optical system to be measured 19 at which the light flux convergence point is detected by the light flux convergence point detection means 9 is obtained (in the embodiment, two-dimensional CC).
The position of the measured optical system 19 where the light flux diameter of the light flux observed as an image by the D sensor 10 is minimized is obtained. )
(Step 12).

After reading and storing the position x ₁ of the optical system 19 to be measured and the position y ₁ of the light flux convergence point detection means 9 (step 13), the light flux convergence point detection means 9 is moved to the second set position. (Step 4).

Hereinafter, steps 2, 3, and 4 are repeated until the set number N of positions of the light beam convergence point detecting means 9 is satisfied.

In the N sets of conjugate arrangements thus obtained,
The position x _i of the optical system to be measured 19 (i = 1, 2, ...,
N) and the position y _i (i = 1, 1) of the light beam convergence point detection means 9.
2, ..., N), the focal length is calculated using the calculating means 18.

[0030]

The principle of focal length calculation used in the present invention will be described with reference to FIG. The object point at a finite position from the lens L is O, the image point of the object point O by the lens L is I, the front (object side) focal position of the lens L is F, and the rear (image side) focal position of the lens L is Let F ′ be the distance between O and F be x, the distance between F ′ and I be y, and the focal length of the lens L be f, then Newton's equation (Equation 4) holds.

[0031]

[Formula 4] x · y = f · f

When the lens L is moved by Δx (the direction in which the lens L moves away from the object point O is positive), the image point I moves in Δ'by Δy (the direction in which the image point I moves away from the lens L is positive). Then, since O and I ′ are conjugates, Formula 5 also holds.

[0033]

(5) (x + Δx) (y + Δy−Δx) = f · f

Therefore, assuming that the lens L is set at _three different locations in the optical axis direction, x ₁ , x ₂ , and x ₃ , and the image points for each are y ₁ , y ₂ , and y ₃ , the _two equations 6 Since the equation is established and Newton's equation (Equation 4) is also established, these three equations are solved as simultaneous equations, and x,
y and f can be calculated by the equation 7.

[0035]

[6] _{(x + (x 2 -x 1} )) (y + (y 2 -y 1)
− (X ₂ −x ₁ )) = f · f (x + (x ₃ −x ₁ )) (y + (y ₃ −y ₁ ) − (x ₃
-X ₁ )) = f · f

[0036]

[Equation 7]

Further, when the lens L is set at different N positions (N ≧ 3) x _i (i = 1, 2, ..., N) in the optical axis direction, the focal length f is set as follows. You can ask. That is, the image point position with respect to the object point x _i is y _i (i =
1, 2, ..., N), the N equations of Equation 8 hold.

[0038]

(8) (x + (x _i −x _j )) (y + (y _i −y _j )
− (X _i −x _j )) = f · f (i = 1, 2, ..., N) (j is an arbitrary integer from 1 to N)

By substituting Newton's equation (Equation 4) into (N-1) equations of Equation 9 and expanding and rearranging both sides, Equation 10 is obtained, and (N-1) equations linear in x and y are obtained. To get

[0040]

(X + (x _i −x _j )) (y + (y _i −y _j )
− (X _i −x _j )) = f · f (i = 1, 2, ..., N, except i = j)

[0041]

(10) ((y _i −y _j ) − (x _i −x _j )) x +
(X _i −x _j ) y = (x _i −x _j ) ((y _i −y _j ) −
(X _i −x _j )) (i = 1, 2, ..., N, except i = j) (j is an arbitrary integer from 1 to N)

By using these (N-1) equations as observation equations and applying the least squares method, x,
y and f can be calculated.

The description has been given separately for the case where there are three measurement points and the case where there are three or more measurement points. However, in the case of N = 3 and j = 1 in the equation 3, the result of the equation 7 agrees, so the equation 3 is the focal length. It becomes a general formula to obtain.

The measuring apparatus and the measuring method of the present invention are constructed on the basis of this principle.
By movably supporting the optical support member 3, the distance between the measured optical system 19 and the object point can be changed.

The amount of movement of the measured optical system 19 can be known by the reading means 6 as the movement of the position of the measured optical system 19. The value read by the reading unit 6 is stored in the storage unit 8 for use in later calculation of the focal length.

The light beam converging point detecting means 9 is connected to the optical support 12.
By movably supporting the light source, the movement of the image point can be known by the reading means 15 as the movement of the position of the light flux convergence point detection means 9 when the light flux convergence point is detected.

The value read by the reading means 15 is stored in the storage means 17 for use in later calculation of the focal length.

It is possible to confirm that the object point and the image point are conjugate by fixing the position of the optical system to be measured 19 and moving the light flux convergence point detection means 9 to detect the light flux convergence point. Also,
The light flux convergence point detection means 9 is fixed and the light flux convergence point detection means 9 is fixed.
The measured optical system 19 may be moved so as to detect the light flux convergence point, and the conjugation between the object point and the image point may be confirmed.

The calculating means 18 calculates the focal length of the measured optical system 19 from the value of the position of the measured optical system 19 and the value of the position of the light beam convergence point detecting means 9 with respect to at least three conjugate arrangements. Have a function.

As described above, according to the present invention, it is possible to measure the focal length with a finite disposition of the object-image distance of the optical system to be measured.

[0051]

EXAMPLE A measuring apparatus of an example will be described in detail with reference to FIG. The measuring apparatus according to the embodiment has a divergent light flux generating means 1
An optical support 3 for movably supporting the optical system to be measured 19 in the direction of the optical axis of the light flux, a reading means 6 for the position of the optical system to be measured 19, and a storage means for the position read by the reading means 6. 8, a light flux convergence point detection means 9 for detecting a convergence point of the light flux from the measured optical system, and an optical support for movably supporting the light flux convergence point detection means 9 in the optical axis direction of the light flux from the measured optical system. The body 12, the reading means 15 at the position of the light flux convergence point detection means 9, and the storage means 1 at the position read by the reading means 15.
7 and a computing means 18 for computing the focal length of the optical system to be measured based on the positional information of the divergent luminous flux generating means 1 and the luminous flux convergence point detecting means 9 stored in the storing means 8 and the storing means 17. . The optical system to be measured 19 is arranged in the divergent light flux from the divergent light flux generation means 1 with their optical axes substantially aligned.

Each part will be described below.

(Divergent light beam generating means 1) semiconductor laser 2
The divergent light flux from is used.

(Optical support 3) The optical bench 5 comprises a stage 4 for holding the optical system to be measured 19 and an optical bench 5.
Is elongated in the optical axis direction of the optical system to be measured.
The stage 4 placed on this is movable in the optical axis direction by a pulse motor and a feed screw (not shown).

(Reading Unit 6) A corner cube (not shown) is attached to the stage 4, and the position of the stage 4 moving integrally with the semiconductor laser 2 with respect to the optical bench 5 is read by the laser interference length measuring device 7. The positive direction is the direction in which the stage 4 (semiconductor laser 2) moves away from the divergent light generating means 1.

(Storage Unit 8) The position information read by the laser interference length measuring device 7 is A / D converted and stored in the storage unit 8.

(Light flux convergence point detecting means 9) The two-dimensional CCD sensor 10. The obtained image is observed on the monitor 11. The two-dimensional CCD sensor 10 is moved in a light beam having a converging point in the optical axis direction of the light beam, and the position where the light beam diameter is the minimum is detected as the converging point.

(Optical support 12) A stage 13 for holding the convergence point detecting means 9 and an optical bench 14 are provided. The optical bench 14 is elongated in the optical axis direction of the light beam emitted from the optical system to be measured. Is. The stage 13 placed on this is movable in the optical axis direction by a pulse motor and a feed screw (not shown).

(Reading means 15) A corner cube (not shown) is attached to the stage 13 and a laser interferometer 16 is installed.
The stage 13 that moves integrally with the convergence point detection means 9
The position of the optical disc with respect to the optical bench 14 is read. The direction is positive when the stage 13 (two-dimensional CCD sensor 10) moves away from the measured optical system 19.

(Storage 17) Laser interferometer 16
The position information read by is A / D converted and stored in the storage unit 1.
Stored in 7.

(Calculating means 18) N positions (N ≧ 3) of the measured optical system 19 stored in the storage means 8 (the stage 4)
Value read as the position of the optical bench 5) x _i
(I = 1, 2, ..., N) and the position of the two-dimensional CCD sensor 10 stored in the storage unit 17 when the convergence point is detected for each position (optical of the stage 13). The value read as the position for the bench 14) y _i (i = 1,
2, ..., N) and the function of calculating the focal length of the optical system to be measured by the equation 11.

[0062]

[Equation 11]

The measuring method of the embodiment will be described with reference to FIGS. 1 and 2.

The set number N of positions of the optical system to be measured 19 (≧
After determining 3), the optical system to be measured 19 is installed at the first setting position so that the optical axis of the light beam from the divergent light beam generating means 1 is guided to the optical system to be measured 19 in a substantially coincident manner. (Step 1).

The light beam convergence point detecting means 9 is moved in the optical axis direction of the light beam, and the position where the light beam diameter is minimum is detected as the light beam convergence point (step 2).

[0066] reads the position y ₁ of the position x ₁ and the light beam converging point detecting means 9 of the measurement optical system 19, after storing (step 3), to move the measurement optical system 19 into a second set position ( Step 4).

Hereinafter, steps 2, 3, and 4 are repeated until the set number N of positions of the optical system to be measured 19 is satisfied. i (1 ≦
From the set position x _{i of the (} i ≦ N) th measured optical system 19 and the corresponding position y _i of the detection means 9, the calculation means 18
The focal length of the optical system to be measured is calculated by.

Another measuring method of the embodiment will be described with reference to FIGS. 1 and 3.

Set number N of positions of the light beam convergence point detecting means 9
After determining (≧ 3), the light flux convergence point detection means 9 is installed at the first setting position (step 11).

The position of the measured optical system 19 for detecting that the luminous flux convergent point detecting means 9 detects the minimum luminous flux diameter is obtained by moving the measured optical system 19 in the optical axis direction (step 12).

After reading and storing the position x ₁ of the optical system 19 to be measured and the position y ₁ of the light flux convergence point detection means 9 (step 13), the light flux convergence point detection means 9 is moved to the second set position. (Step 14).

Thereafter, steps 12, 13, and 14 are repeated until the set number N of positions of the light beam convergence point detecting means 9 is satisfied. The focal length of the optical system to be measured is calculated by the calculating means 18 from the set position x _{i of the} i (1 ≦ i ≦ N) th measured optical system 19 and the corresponding position y _i of the detecting means 9.

The present invention is not limited to the above embodiment. As a means for detecting the convergence point of the light flux, a one-dimensional line sensor may be placed in the light flux to detect the location where the light flux diameter is minimum.

Further, the detecting means as shown in FIG. 5 may be used. That is, it is composed of a pinhole 20, a relay lens 21, and a photoelectric conversion element 22, and the photoelectric conversion element 22 is arranged at a conjugate position of the relay lens 21 of the pinhole 20. When this detecting means is moved in the optical axis direction of the light beam having the convergence point, the output of the photoelectric conversion element 22 becomes maximum when the pinhole 20 coincides with the convergence point of the light beam, and the convergence point can be detected.

Alternatively, the structure using the interference pattern shown in FIG. 6 may be used. That is, the reflection means 27 provided in the light flux of the divergent light flux generation means 1 including the laser light source 23 and the lenses (24, 25, 26) for retroreflecting a part of the light flux along the optical path that came, and the optical system under test. The reflecting means 28 for retroreflecting the luminous flux emitted from 19 is constituted.

When the reflecting means 28 has a concave surface as shown in FIG. 6, it is arranged behind the converging point, and when the spherical center of the concave surface coincides with the converging point of the light beam, it goes backward along the optical path along which the light beam comes. Since the light is reflected, an interference pattern is obtained by the interference with the light flux reflected by the reflection means 27. When the reflecting means 28 is a convex surface, it is arranged closer to the optical system 19 to be measured than the converging point, and when the spherical center of the convex surface coincides with the converging point of the luminous flux, it is retroreflected along the optical path where the luminous flux came. An interference pattern is obtained by the interference with the light flux reflected by the reflection means 27. When the reflection means 24 is a plane, when the convergence point of the light flux is on that plane, the light flux is reflected symmetrically with respect to the optical axis and interferes with the light flux reflected by the reflection means 27 to obtain an interference pattern.

In any case, the interference pattern is the lens 3
Two-dimensional CCD sensor 31, monitor 32 through 0
Observed in. In this way, the reflection means 28 is used as a convergence point detection means.

Further, the divergent light beam generating means may be composed of an incoherent light source and a lens, and the convergence point detecting means may be an optical system having an eyepiece lens, and the convergence point may be visually judged. The divergent light beam generation means may be configured by using a white light source and a monochromator that is a spectroscopic means, and may be configured to measure the difference in focal length depending on the wavelength of the optical system to be measured.

As for the calculation means, in the embodiment, it is shown that the equation 11 obtained by setting j = 1 in the equation 3 is used, but it is not limited to j = 1. j can be selected from 1 to N in N ways. Also, in Equation 3, j is 1
It is also possible to obtain the focal length value by averaging a part or all of the values obtained from N to N calculations.

As the optical system to be measured, the arrangement in the case of the refraction system is shown in the embodiment, but as shown in FIG. 7, the light beam from the divergent light beam generating means 1 is reflected by the optical system 34 to be measured,
By arranging the light flux by the half mirror 33 to guide it to the detecting means 9 of the light flux convergence point, it is possible to measure the focal length of the reflection system optical system.

[0081]

As described above, according to the present invention, since the object-image distance can be measured in a finite arrangement, it can be used in a finite amount such as an optical disk objective lens, a copying machine lens, a facsimile lens, etc. The optical system designed for this purpose can be measured in an arrangement very close to that in actual use, with almost no influence of aberration caused by the difference in arrangement.

The nodal slide method described in the section of the prior art is complicated in that the lens and the movement in the optical axis direction are alternately repeated in order to place the nodal point of the test lens on the rotary axis of the nodal slide base. Although an operation requiring skill is required, in the present invention, only the operation of moving the divergent light generation means and the convergence point detection means in the optical axis direction is required, and the measurement is easy. Further, in the magnification method, a collimator lens having a known focal length and an index having a known dimension are required. However, in the present invention, in addition to the scale used for the moving amount reading means of the stage on the optical bench, the optical characteristic or Does not require a reference of known dimensions.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a focal length measuring device for an optical system according to the present invention.

FIG. 2 is a process chart showing the procedure of an embodiment of a method for measuring the focal length of an optical system according to the present invention.

FIG. 3 is a process chart showing the procedure of another embodiment of the method for measuring the focal length of an optical system according to the present invention.

FIG. 4 is a block diagram of an optical system to be measured, which is used to explain the principle of measuring the focal length of the optical system of the present invention.

FIG. 5 is a configuration diagram of a modified example of the light beam convergence point detection means in the optical system focal length measurement device of the present invention.

FIG. 6 is a configuration diagram of another modified example of the light beam convergence point detection means in the focal length measuring device for an optical system according to the present invention.

FIG. 7 is a configuration diagram showing an arrangement when the present invention is applied to a reflective concave mirror.

FIG. 8 is a block diagram of a conventional focal length measuring device by a nodal slide method.

FIG. 9 is a block diagram of a conventional focal length measuring device using a magnification method.

[Explanation of symbols]

 1: Divergent light flux generating means 2: Semiconductor laser 3: Optical support 4: Mounting table 5: Optical bench 6: Reading means 7: Laser interferometer 8: Storage means 9: Convergence point detection means 10: Two-dimensional CCD Sensor 11: Monitor 12: Optical support 13: Mounting table 14: Optical bench 15: Reading means 16: Laser interferometer 17: Storage means 18: Computing means 19: Measured optical system 20: Pinhole 21: Relay Lens 22: Photoelectric conversion element 23: Laser light source 24: Lens 25: Lens 26: Lens 27: Reflecting means 28: Reflecting means 29: Half mirror 30: Lens 31: Two-dimensional CCD sensor 32: Monitor 33: Half mirror 34: Target Measurement optical system 51: Light source 52: Mark line 53: Collimator lens 54: Sliding table 55: Rotating table 56: Nodal slide table 57: Optical bench 58: Microscope 59: Test lens 60: Light source 61: Standard plate 62: Collimator lens 63: Microscope 64: Focal plane of test lens

Claims (5)

[Claims] 1. A divergent light beam generating means, an optical support for movably supporting an optical system to be measured in its optical axis direction, a reading means for reading the position of the measured optical system, and a position read by the reading means. The storage means, the light flux convergence point detection means for detecting the convergence point of the light flux emitted from the optical system to be measured, and the light flux convergence point detection means are movably supported in the optical axis direction of the light flux emitted from the optical system to be measured. The focal length of the optical system to be measured is calculated from the optical support, the reading unit for the position of the detecting unit, the storage unit for the position read by the reading unit, the position of the measured optical system, and the position of the light beam convergence point detecting unit. An apparatus for measuring a focal length of an optical system, comprising: a calculating means for calculating. 2. The positions of at least three N measured optical systems are set to x _i (i = 1, 2, ..., N), and the position of the light beam convergence point detection means is set to y _i (i = 1). , 2, ..., N)
In this case, the calculation means for calculating the focal length according to claim 1 is the calculation means for calculating the focal length according to the equation (1). [Equation 1] 3. At least three steps of moving the light flux convergence point detection means to detect the convergence point of the light flux from the optical system to be measured.
The focal length of the optical system is characterized in that the focal length of the optical system to be measured is obtained from the position of the optical system to be measured and the position of the light flux convergence point detection means at each position. Measuring method. 4. The method of moving the optical system to be measured to obtain the position at which the convergence point of the light beam emitted from the optical system to be measured is detected by the light beam convergence point detecting means, at least at three light beam convergence point detecting means. A method for measuring the focal length of an optical system, characterized in that the focal length of the optical system to be measured is obtained from the positions of the light flux convergence point detecting means and the position of the optical system to be measured in each position. 5. A position x of at least three optical systems to be measured.
_{From i} (i = 1, 2, ..., N) and the position of the light beam convergence point detection means y _i (i = 1, 2, ..., N),
The focal length of the optical system to be measured is calculated by the following method. [Equation 2]