JPH0763649A - Apparatus and method for measuring focal length of divergence optical system - Google Patents

Abstract

(57) [Summary] [Object] To provide an apparatus and method for measuring the focal length of a divergent optical system. Constitution: A means 1 for generating a convergent light flux incident on an optical system to be measured which is movably supported, an optical support 14 for movably supporting an optical system to be measured 21, and a light flux emitted from the optical system to be measured 21. And the position of the measured optical system 21 and the convergent light beam generation unit 1 where the light beam convergence point is detected.

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 Conventionally, an invention described in JP-A-5-142094 has been reported as a device for measuring the focal length of a concave lens. This conventional technique will be described with reference to FIG.
A test concave lens 52 is placed in the convergent light beam 51, and the fact that the convergent light beam 51 is converted into a parallel light beam 54 by the test concave lens 52 when the convergence point 53 of the convergent light beam and the imaginary focal point of the test concave lens coincide with each other. Using the observation telescope 55, the position in the optical axis direction of the test concave lens 52 in which the light emitted from the test concave lens 53 becomes a parallel light flux is determined, and the position of the surface of the test concave lens at that time and the convergent light flux incident on the test concave lens are determined. In this method, the focal length of the concave lens to be tested is defined as the distance f from the convergence point.

[0003]

The focal length is defined by the focal point,
Regarding the distance from the principal point, conventionally, the lens surface is used instead of the principal point of the lens, and there is a problem that an accurate focal length cannot be measured.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes a convergent light beam generating means, an optical support for movably supporting the convergent light beam generating means, and a convergent light beam. A reading means for the position of the generating means, a storage means for the position of the convergent light flux generating means read by the reading means, an optical support for movably supporting the optical system to be measured in its optical axis direction, and an optical to be measured. A reading unit for reading the position of the system, a storage unit for reading the position read by the reading unit, a light beam convergence point detecting unit for detecting a convergence point of the light beam emitted from the optical system to be measured, and a position and a target of the convergent light beam generating unit. From the position of the measurement optical system,
There is provided a measuring device for a focal length of a divergence system optical system, comprising: an arithmetic means for calculating a focal length of an optical system to be measured.

Further, according to the present invention, at least three positions of the convergent light beam generating means at N positions are set to x _i (i = 1, 2, ...).
, N), and the position of the measured optical system is y _i (i = 1, 1,
2, ..., N), the arithmetic means for calculating the focal length is an arithmetic means for calculating by the formula (3).

[0006]

[Equation 3]

Further, according to the present invention, the optical system to be measured is moved,
The position where the convergence point of the light flux emitted from the optical system to be measured is detected by the light flux convergence point detection means is determined for at least three positions of the converged light flux generation means, and Provided is a method for measuring the focal length of a divergence system optical system, which is characterized in that the focal length of the system under measurement is obtained from the position and the position of the system under measurement.

Further, according to the present invention, the convergent light beam generating means is moved to 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. The focal length of the divergence 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 convergent light beam generating means in each position of the optical system. The measurement method of is provided.

Further, according to the present invention, there are at least three positions x _i (i = 1, 2, ..., N) of the convergent light beam generating means.
And the position of the optical system to be measured is y _i (i = 1, 2, ...,
N) is used to calculate the focal length of the optical system to be measured by Equation 3, and a method for measuring the focal length of the divergent optical system is provided.

The structure of the measuring apparatus of the present invention will be described with reference to FIG. The measuring apparatus of the present invention is a convergent light beam generating means 1 (laser light source 2, convex lens 3, convex lens 4 in the embodiment).
An optical support 5 (in this embodiment, the stage 6 and the optical bench 7) for movably supporting the convergent light beam generating means 1 in the optical axis direction of the light beam, and a reading means 8 for reading the position of the convergent light beam generating means 1. (In the embodiment, the laser interferometer length measuring device 9), the storage means 10 for the position read by the reading means 8, and the optical system to be measured 21 are supported movably in the optical axis direction (optical support 14). In the example, the stage 15 and the optical bench 16)
Reading means 17 for the position of the measured optical system 21 (laser interferometer length measuring device 18 in the embodiment), storage means 19 for the position read by the reading means 17, and the luminous flux emitted from the measured optical system 21. Light flux convergence point detection means 11 for detecting a convergence point
(A two-dimensional CCD sensor 12 in the embodiment), a storage unit 10, and a calculation unit 20 for calculating the focal length of the optical system to be measured from the values stored in the storage unit 19.

Next, the measuring method of the present invention will be described with reference to FIGS. 1 and 2. The measuring method of the present invention comprises the following steps. After the set number N (≧ 3) of the positions of the convergent light beam generating means 1 is determined, the convergent light beam generating means 1 is installed at the first setting position (step 1).

The measured optical system 21 is moved in the direction of its optical axis, and the position of the measured optical system 21 at which the light beam convergence point detection means 11 detects the light beam convergence point is obtained (in the embodiment, a two-dimensional CC).
The position of the measured optical system 21 at which the light flux diameter of the light flux observed as an image by the D sensor 12 is minimized is obtained. )
(Step 2).

After reading and storing the position x _{1 of} the convergent light beam generating means 1 and the position y ₁ of the optical system to be measured 21 (step 3), the convergent light beam generating means 1 is moved to the second set position ( Step 4).

Hereinafter, the set number N of positions of the convergent light beam generating means 1 will be described.
Repeat steps 2, 3, and 4 until the above is satisfied. Converging light beam generation means 1 in the N sets of conjugate arrangements thus obtained
From the set position x _{i i} (i = 1, 2, ..., N) of the target optical system 21 and the position y _i (i = 1, 2, ..., N) of the measured optical system 21,
The calculation means 20 is used to calculate the focal length.

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 determining the set number N (≧ 3) of the positions of the optical system 21 to be measured in the optical axis direction, the optical system 21 is installed at the first set position (step 11).

The convergent light beam generating means 1 is connected to the measured optical system 21.
The position of the converged light beam generation means 1 at which the light beam convergence point detection means 11 detects the light flux convergence point is obtained (in the embodiment, the light flux diameter of the light flux observed as an image by the two-dimensional CCD sensor 12). The position of the convergent light flux generating means 1 that minimizes is obtained) (step 12).

After reading and storing the position x _{1 of the} convergent beam generating means 1 and the position y ₁ of the measured optical system 21 (step 13), the measured optical system 21 is moved to the second set position (step). 14).

Hereinafter, steps 2, 3, and 4 are repeated until the set number N of positions of the optical system to be measured 21 is satisfied. Thus the N sets of conjugated arrangement determined, setting the position of the convergent light beam generating means _{1 x i (i = 1,2,} ···, N) and the position y _{i (i} = 1,2 of the measurement optical system 21 , ..., N), the focal length is calculated using the calculating means 20.

[0019]

The principle of focal length calculation used in the present invention will be described with reference to FIG. Let O be the convergence point of the convergent light beam incident on the lens L, that is, the object point, I be the convergence point of the light beam refracted by the lens L, that is, the image point, and F and F ′ are the focal positions of the lens L. x, F'and the distance between I and y, lens L
Assuming that the focal length of f is f, the object point O and the image point I are conjugate, so Newton's equation

[0020]

[Formula 4] x · y = f · f

Is satisfied. When the object point O is moved to Δ ′ by Δx (the direction in which the object point O moves away from the lens is positive), and the lens L is moved in Δy (the direction in which the lens L approaches the object point O is positive), the image point If I does not move, O'and I are also conjugate

[0022]

(5) (x−Δx + Δy) (y−Δy) = f · f

The above also holds. Therefore, the object points are set at _three different points x ₁ , x ₂ , and x ₃ in the optical axis direction,
If there is no movement of the image point position when the lens position is y ₁ , y ₂ and y ₃ for each,

[0024]

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

Since ## EQU3 ## is established, and also Equation 4 is established,
By solving these three equations as simultaneous equations, x, y, and f can be obtained by the equation 7.

[0026]

[Equation 7]

Further, when the object point O is set at N different points (N ≧ 3) x _i (i = 1, 2, ..., N) in the optical axis direction, the focal length f is as follows. Can be asked.
The lens position where the image point position with respect to the object point x _i does not move is y _i
(I = 1, 2, ..., N),

[0028]

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

The N expressions of are established. Equation (N-1)
Substituting equation 4 into this equation and expanding and rearranging both sides,

[0030]

## EQU9 ## − (y _i −y _j ) x + (− (x _i −x _j ) +
(Y _i −y _j )) y = − (y _i −y _j ) ((x _i −x
_j )-(y _i- y _j )) (i = 1, 2, ..., N, except i = J) (j is an arbitrary integer from 1 to N)

And (N-1) which is linear in x and y
Get an expression. By using these (N-1) equations as observation equations and applying the least squares method, x,
It is possible to obtain y and f.

The description has been made 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 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, and the position of the object point is changed by movably supporting the convergent light beam generating means 1 by the optical support 5. it can.

The optical system to be measured 21 is moved by movably supporting the optical system to be measured 21 with an optical support 14. By moving the optical system to be measured 21 with respect to the position of the convergent light beam generation unit 1 and obtaining the position where the light beam convergence point detection unit 11 detects the light beam convergence point, it is possible to determine that the object point and the image point are conjugate. You can check.

Further, with respect to the position of the optical system to be measured 21,
The optical system to be measured 21 may be moved so that the light flux convergence point detection means 11 detects the light flux convergence point, and the conjugate of the object point and the image point may be confirmed.

The calculating means 20 calculates the focal length of the measured optical system 21 from the value of the position of the measured optical system 21 and the value of the position of the light beam convergence point detecting means 11 with respect to at least three conjugate arrangements. Have a function. As described above, the present invention makes it possible to measure the focal length of the divergent optical system.

[0037]

EXAMPLE A measuring apparatus of an example will be described with reference to FIG.
The measuring apparatus of the embodiment includes a convergent light beam generating means 1, an optical support 5 for movably supporting the convergent light beam generating means 1 in the optical axis direction of the light beam, and a reading means 8 for reading the position of the convergent light beam generating means 1. , Storage means 10 for the position read by the reading means 8
An optical support 14 for movably supporting the optical system to be measured 21 in the optical axis direction, a reading unit 17 for the position of the optical system 21 to be measured, and a storage unit 19 for the position read by the reading unit 17. The light flux convergence point detection means 11 for detecting the convergence point of the light flux from the measured optical system 21, the converged light flux generation means 1 stored in the storage means 10 and the storage means 19, and the position information of the measured optical system 21. And a calculation means 20 for calculating the focal length of the optical system to be measured.

The optical system to be measured 21 comprises the convergent light beam generating means 1
The optical axis is substantially aligned with the light flux from. The respective parts will be described below. (Convergent light flux generating means 1) The light flux from the laser light source 2 is used as a convergent light flux by using the convex lens 3 and the convex lens 4.

(Optical support 5) It is composed of a stage 6 for holding the convergent light beam generating means 1 and an optical bench 7. Optical bench 7
Indicates that the light flux of the convergent light flux generation means 1 is elongated in the optical axis direction. The stage 6 placed on this is movable on the optical bench 7 by a pulse motor and a feed screw (not shown).

(Reading means 8) A corner cube (not shown) is attached to the stage 6, and the position of the stage 6 which moves integrally with the convergent beam generation means 1 with respect to the optical bench 7 is read by the laser interferometer length measuring device 9. The direction is positive when the stage 6 (convergent light beam generating means 1) approaches the optical system 21 to be measured.

(Storage Means 10) The position information read by the laser interferometer length measuring device 9 is A / D converted and stored in the storage means 10.
Memorized in. (Light flux convergence point detection means 11) Two-dimensional CCD sensor 12
Is. The obtained image is observed on the monitor 13. When the diameter of the light beam focused on the two-dimensional CCD sensor 12 is minimum, it is determined that the image plane of the optical system to be measured is on the two-dimensional CCD sensor.

(Optical support 14) The optical bench 16 comprises a stage 15 for holding an optical system 21 to be measured and an optical bench 16. The optical bench 16 is elongated in the optical axis direction of the optical system to be measured. The stage 15 placed on this is movable in the optical axis direction by a pulse motor and a feed screw (not shown).

(Reading means 17) A corner cube (not shown) is attached to the stage 15, and a laser interferometer 18 is used.
The stage 15 that moves integrally with the optical system 21 to be measured by
The position of the optical axis with respect to the optical bench 16 is read. The direction is positive when the stage 15 (two-dimensional CCD sensor 12) approaches the light beam convergence point detection means 11.

(Memory means 19) Laser interferometer 18
The position information read by is A / D converted and stored in the storage unit 1.
9 is stored.

(Calculating means 20) Positions (values read as positions of the stage 6 with respect to the optical bench 7) of the convergent light beam generating means 1 at N locations (N ≧ 3) having a conjugate relationship x _i (i
, 1, 2, ..., N) and the position of the measured optical system 21 (value read as the position of the stage 15 with respect to the optical bench 16) y _i (i = 1, 2, ..., N) ) And the equation (10), the focal length of the optical system to be measured is calculated.

[0046]

[Equation 10]

The measuring method of the embodiment will be described with reference to FIGS. 1 and 2. The set number N of the positions of the convergent light beam generation means 1 (≧
After determining 3), the light flux from the convergent light flux generation means 1 is guided to the optical system 21 to be measured so as to substantially coincide with the optical axis.
The convergent light flux generating means 1 is installed at the first setting position (step 1). The light flux convergence point detection means 11 obtains the position of the measured optical system 21 which detects that the diameter of the light flux is the minimum by moving the measured optical system 21 in the optical axis direction (step 2).

After reading and storing the position x _{1 of the} convergent light beam generating means 1 and the position y ₁ of the measured optical system 21 (step 3), the convergent light beam generating means 1 is moved to the second set position (step 3). 4). Hereinafter, steps 2, 3, and 4 are repeated until the set number N of positions of the convergent light beam generating means 1 is satisfied.

N sets of convergent light flux generating means 1 thus obtained
The set position x _i (i = 1, 2, ..., N) and the position y _i (i = 1, 2, ..., N) of the measured optical system 21 are measured by the calculation means 20. Calculate the focal length of the optical system.
Further, another measuring method of the embodiment will be described with reference to FIGS. After the set number N (≧ 3) of the positions of the optical system to be measured 21 is determined, the light beam from the convergent light beam generating means 1 is guided to the optical system to be measured 21 so as to be substantially aligned with the optical axis. The optical system 21 is installed at the first setting position (step 1
1).

The position of the convergent light flux generating means 1 for detecting that the light flux convergent point detecting means 11 detects that the light flux diameter is minimum is obtained by moving the convergent light flux generating means 1 in the optical axis direction of the light flux (step 12). ). The position x _{1 of the} convergent light beam generation means 1 and the position y ₁ of the measured optical system 21 are read,
After storing (step 13), the measured optical system 21 is moved to the second set position (step 14).

Below, the set number N of positions of the optical system 21 to be measured is set.
Repeat steps 12, 13, and 14 until the following is satisfied.
The set positions x of the N sets of convergent light beam generation means 1 thus obtained
_{From i} (i = 1, 2, ..., N) and the position y _i (i = 1, 2, ..., N) of the measured optical system 21, the focus of the measured optical system is calculated by the calculating means 20. Calculate the distance.

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, the pinhole 22, the relay lens 23,
It is composed of a photoelectric conversion element 24, and the photoelectric conversion element 24 is arranged at a conjugate position of the pinhole 22 by the relay lens 23. When this detecting means is moved in the optical axis direction of the light flux having the convergence point, the output of the photoelectric conversion element 24 becomes maximum when the pinhole 22 coincides with the convergence point of the light flux, and the convergence point is detected. Is possible.

Alternatively, the structure using the interference pattern shown in FIG. 6 may be used. That is, the laser light source 25, the lens (2
6, 27, 28) provided in the light flux of the convergent light flux generation means 1 and reflecting means 29 for retroreflecting a part of the light flux along the optical path along which the light flux is emitted after being emitted from the optical system 21 to be measured. The reflecting means 30 for reflecting the light is used.

When the reflecting means 30 is a concave surface as shown in the drawing, 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 is retroreflected along the optical path along which the light beam comes. Therefore, an interference pattern is obtained by the interference with the light flux reflected by the reflecting means 29. When the reflecting means 30 is a convex surface, the reflecting means 30 is arranged closer to the optical system 21 to be measured than the converging point, and when the spherical center of the convex surface coincides with the converging point of the light beam, it is retroreflected along the optical path where the light beam came. An interference pattern is obtained by the interference with the light flux reflected by the reflection means 29.

When the reflecting means 30 is a plane, when the convergence point of the light beam is on the plane, the light beam is reflected symmetrically with respect to the optical axis and interferes with the light beam reflected by the reflecting means 29 to obtain an interference pattern. . In any case, the interference pattern is observed by the two-dimensional CCD sensor 33 and the monitor 34 via the lens 32. In this way, the reflection means 30 is used as a convergence point detection means.

Further, the converging light beam generating means may be composed of an incoherent light source and a lens, and the converging point detecting means may be an optical system having an eyepiece lens, and the converging point may be visually judged. The convergent light beam generating means may be configured by using a white light source and a monochromator as 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.

With respect to the calculating means, in the embodiment, it is shown that the equation 10 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 refracting system is shown in the embodiment, but as shown in FIG. 7, the light beam from the convergent light beam generation means 1 is reflected by the optical system 36 to be measured,
By arranging the light flux by the half mirror 35 to guide it to the detecting means 11 of the light flux convergence point, the focal length of the reflection optical system can be measured.

[0059]

As described above, according to the present invention, in addition to the scale used for the moving amount reading means of the stage on the optical bench, a reference object having known optical characteristics or dimensions is not required. The focal length of the diverging optical system can be measured with high accuracy.

[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 convex mirror.

FIG. 8 is a configuration diagram of a conventional focal length measuring device.

[Explanation of symbols]

 1: Convergent light beam generation means 2: Laser light source 3: Convex lens 4: Convex lens 5: Optical support body 6: Support table 7: Optical bench 8: Reading means 9: Laser interferometer 10: Storage means 11: Convergence point detection Means 12: Two-dimensional CCD sensor 13: Monitor 14: Optical support 15: Mounting table 16: Optical bench 17: Reading means 18: Laser interference measuring device 19: Storage means 20: Computing means 21: Optical system to be measured 22 : Pinhole 23: Relay lens 24: Photoelectric conversion element 25: Laser light source 26: Lens 27: Lens 28: Lens 29: Reflecting means 30: Reflecting means 31: Half mirror 32: Lens 33: Two-dimensional CCD sensor 34: Monitor 35 : Half mirror 36: Optical system to be measured 51: Convergent light beam 52: Concave lens to be measured 53: Converging light beam convergence point 54: Parallel light 55: infinity observation telescope

Claims (5)

[Claims] 1. A convergent light beam generating means, an optical support for movably supporting the convergent light beam generating means, a reading means for reading the position of the convergent light beam generating means, and a position for the convergent light beam generating means read by the reading means. Storage means, an optical support for movably supporting the optical system to be measured in the optical axis direction thereof, reading means for reading the position of the optical system to be measured, storage means for the position read by the reading means, and optical to be measured. A light flux convergence point detecting means for detecting a convergence point of a light flux emitted from the system, and an arithmetic means for calculating a focal length of the measured optical system from the position of the converged light flux generating means and the position of the measured optical system are provided. A device for measuring the focal length of a divergent optical system. 2. The positions of at least three convergent light flux generating means at N positions are x _i (i = 1, 2, ... N), and the positions of the optical system to be measured are y _i (i = 1, 2,). , ..., N), the calculation means for calculating the focal length according to claim 1 is the calculation means for calculating the focal length according to equation (1). [Equation 1] 3. A method of moving a measured optical system to obtain a position at which a convergence point of a light beam emitted from the measured optical system is detected by a light beam convergence point detecting means, at least at three convergent light beam generating means. A method for measuring the focal length of a divergence system optical system, characterized in that the focal length of the optical system to be measured is obtained from the positions of the convergent light beam generating means and the position of the optical system to be measured in each position. 4. At least three positions of the optical system to be measured are obtained by moving the convergent light beam generating means and obtaining a 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. The method for measuring the focal length of the divergence system optical system is characterized in that the focal length of the optics system to be measured is obtained from the position of the optical system to be measured and the position of the convergent light beam generating means in each case. 5. The positions x _i (i = 1, 2, ..., N) of the convergent light beam generating means and the positions of the optical system to be measured are y _i (i = 1, 2, ... ., N), the focal length of the optical system to be measured is calculated by the equation 2, and the method of measuring the focal length of the divergent optical system according to claim 3 or 4. [Equation 2]