JPS58139044A - Measuring method for focus distance and distance between principal points of lens - Google Patents

Abstract

PURPOSE:To simultaneously determine a focus distance and a distance between principal points of a lens to be measured, by a method wherein an uniform light source, a slit, a lens to be measured, and an image sensor are aligned in a row, and from 2 types of position relations, a distance between the slit and the image sensor and an image pickup magnification are determined. CONSTITUTION:On an optical bench 31, an uniform light source 32, a slit 33, a lens part 34 to be measured, and a linear image sensor part 35 are aligned in a row in order named. The lens part 34 consists of a lens 340 to be measured and a moving lens 341, and the sensor part 35 consists of a linear image sensor 350, a sensor moving table 351, and a display circuit part 352. The bench 31 is marked with graduation 310 for measuring a position. The sensor part 35 is secured to a given position, and the lens part 34 is moved so that a slit image is formed on the sensor part 350. The position of the sensor part 35 is measured from the graduation 310, a length of an image is found by multuplying the display value of the circuit part 352 by the element pitch of the sensor 350 to compute an image pickup magnification. The operations are conducted two times by changing the position of the sensor part 35, and this enables to compute a focus distance and a distance between principal points.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the focal length and distance between principal points of a lens.

Generally, in optical measuring instruments using lenses, it is often necessary to accurately set the imaging magnification. The imaging magnification is set by calculating the distance between the object point and the image point corresponding to a predetermined imaging magnification, and setting the distance between the object point and the image point according to the calculated value. When calculating the distance between the object point and the image point corresponding to the imaging magnification, it is necessary to know the focal length f of the lens used and the principal point interval ΔH.

Conventionally, the focal length f and the principal point interval ΔH have been determined using different methods. FIG. 1 is a diagram for explaining the conventional method of determining the focal length f.

A collimator lens 2 for imaging is arranged in front of the point light source 1. With this configuration, first collimator lens 2
The position of the first quadrant 8, which is the normal imaging position, is measured using a microscope. Next, the lens to be measured 4 is placed on the refracted beam of the collimator lens 2, and the position of the second image point 5 is measured using a microscope. The image point movement distance is determined from the positions of the first image point 3 and second image point 5 determined in this way, and the focal length f is calculated. This type of method is expected to provide accurate measurement. However, it requires a precise mechanism of the device and skill of the measurer, and the principal point spacing △H has to be determined by a method different from the above method, which is time-consuming. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for measuring the focal length and distance between principal points of a lens, which eliminates the above-mentioned conventional problems.

To summarize, this invention arranges a slit at the object point and an image sensor at the image point of a lens to be measured, and allows the object point and image point to be connected in two different positional relationships with different relative positions. It is characterized by measuring the distance and the imaging magnification between the object and the image, and simultaneously determining the focal length and principal point distance of the lens to be measured based on two measured values of the distance and the imaging magnification in one operation. do.

Hereinafter, the principle and embodiments of this invention will be explained with reference to drawings.

FIG. 2 is a diagram for explaining the invention in detail.

In FIG. 2, an object 11 of length L is attached to a lens to be measured 12.
is arranged at a distance a from the first principal point H1 of
An image 13 having a length l is formed at a position at a distance from the second principal point H2. The imaging magnification M in this case is M = -Q). Also, by modifying Newton's imaging formula and using equation (1), a=f(1+-)' (3a) also becomes = f(1
+M) (8b). Object 11 and image 1
The distance A from 3 is A=a+t+△H (where △H is the distance between principal points HIH2), and the Kono equation and equations (3a) and (8b)
If a, 11> is deleted from , , IA=(2+M+-)f+ΔH(4).

Now, two distances A between the object 11 and the image 18 are set in advance as A1 and A2, and the flaw lengths corresponding to the distances A1 and A2 are il.
, A2, the corresponding imaging magnification M, ,
M2 is when the object length is L. Next, equations (4), (5a), (5b), (6a),
From (6b), −, Al, and A2 become 1 f+ΔH(7a) for AI= and 2 f+ΔH(7b) for A2=. Expressions (7a) and (7b) are converted into a binary system of f and △H.
This can be solved as the following equation.

In this way, from equations (8) and (9), the distances AI and A2 between the object point and the image point, and 1 sK corresponding to each distance.
2 (that is, the imaging magnification Mt, M2), both the focal length f and the principal point interval ΔH can be obtained.

Next, a method of determining an imaging magnification corresponding to a predetermined distance between an object point and an image point, which is an embodiment of the present invention, will be described.

FIG. 8 is a diagram for explaining a method of determining an imaging magnification corresponding to a predetermined distance between an object point and an image point, which is an embodiment of the present invention.

In the figure, a uniform light source 21, a slit 22 having the same width as the slit, a lens to be measured 28, and a linear image sensor 24 are arranged in a line. The slit 22 and the linear image sensor 24 are fixed at a predetermined distance, and the lens to be measured 28
The position of is adjusted so that a slit image is formed on the linear image sensor 24. Linear image sensor 24
A detection signal corresponding to the number of elements of the linear image sensor 24 corresponding to this flaw length is output. This output is a pulse train signal and is input to the display circuit section 25. The display circuit section 25 includes an amplifier circuit 251, a waveform shaping circuit 252,
It is formed by a counting circuit 253 and a display device 254. The amplifier circuit 251 amplifies the pulse train to a certain level and inputs its output to the waveform shaping circuit 252. Waveform shaping circuit 25
2 shapes the amplified signal into a waveform that is easy to count, and inputs the output to the counting circuit 258. Counting circuit 2
53 counts the pulse train having a waveform, and the counting result is displayed on the display device 254. By multiplying this count by the element pinch of the linear image sensor 24, the flaw length is given, and the imaging magnification is determined.

In this way, by setting two distances between the Surin・') 22 and the linear image sensor 24, finding the imaging magnification corresponding to each distance using the method described above, and substituting it into equations (8) and (9), The focal length f and the principal point interval ΔH can be determined simultaneously.

FIG. 4 is a diagram showing a specific apparatus configuration of the method according to the embodiment of the present invention.

In FIG. 4, a uniform light source 32,
The slit 33, the lens section to be measured 34, and the linear image sensor section 35 are arranged in a line in this order. The lens to be measured section 34 includes a lens to be measured 840 and a lens movable table 84.
1, and the linear image sensor section 35 is composed of a linear image sensor 350, a sensor movable table 351, and a display circuit section 352, all of which are capable of sliding on the optical bench 31. A vernier scale 310 for position measurement is formed on the optical bench 31. In such a configuration, the linear image sensor section 35 is fixed at a predetermined position, and the lens section 84 to be measured is moved so that a slit image is formed on the linear image sensor 850. In which state, the position of the linear image sensor section 35 is measured with the scale 31O, and the display device of the display circuit section 852 (
(not shown) is multiplied by the element pitch of the linear image sensor 850 to determine the flaw length and calculate the imaging magnification. Perform this operation twice by changing the position of the linear image sensor section 35, and calculate the distance between the slit 38 and the image sensor section 85 obtained from these measurements and the imaging magnification corresponding to each distance using the formula By substituting into (8) and (9), the focal length f and principal point interval ΔH are determined.

As described above, according to the present invention, the focal length and principal point distance of the lens to be measured can be determined simultaneously with a simple configuration and no skill required, and with -1 operations. A distance measurement method can be provided.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the conventional method of determining focal length, Fig. 2 is a diagram for explaining the present invention in detail, and Fig. 3 is a diagram for explaining the method of determining the focal length that has been used in the past. FIG. 4 is a diagram for explaining a method of determining an imaging magnification corresponding to a predetermined distance from an image point, and FIG. 4 is a diagram showing a specific device configuration of the method according to an embodiment of the present invention. 21... Uniform light source, 22... Slit, 23...
... Lens to be measured, 24... Linear image sensor. Applicant Tateishi Electric Co., Ltd. Agent Patent Attorney Hisao Komori Figure 1 8 w! Figure 4

Claims (1)

[Claims] (1) A uniform light source, a slit, a lens to be measured, and an image sensor are arranged in a line in this order, and the relative positions of the slit and the image sensor are different, and the slit image is formed on the image sensor. In each case, the distance between the slit and the image sensor is measured in terms of positional relationship, and the imaging magnification is determined from the output value of the image sensor corresponding to the slit width, and each of these distances and the imaging magnification is set by two. A method for measuring focal length and principal point spacing of a lens, in which the focal length and principal point spacing of a lens to be measured are simultaneously calculated from measured values.