RU2025692C1 - Method of measurement of characteristics of optical systems: focal distances and decentering - Google Patents

Abstract

FIELD: optical instrumentation engineering. SUBSTANCE: method of measurement of characteristics of optical systems: focal distances, focal lengths and decentering lies in that converging light beam is focused close to front focal plane of auxiliary lens. Investigated optical system is placed near point in which focused converging light beam is focused. Size of section of light beam in rear focal plane of auxiliary lens is measured. Relative position of point in which converging light beam is focused is changed (in time or space) with reference to vertex of front surface of investigated system, size of section of light beam in rear focal plane of auxiliary lens is measured and required characteristic of investigated optical system is found from comparison of sizes of sections. EFFECT: improved authenticity and accuracy of measurements. 3 cl, 3 dwg

Description

 The invention relates to optical instrumentation and can be used to measure focal lengths and decentration of optical systems.

 A known method of measuring the rear focal segments of the lens [1], in which a parallel beam of light is directed to the lens and the distance between the top of the last surface of the lens and the plane in which the parallel beam of light is focused after the lens is measured.

 When measuring the focal segment, the microscope is focused on the top of the last lens surface and a count is taken on the displacement scale, then the microscope is focused on the image of the test object and a second count is taken. The difference of the samples corresponds to the focal segment.

 The disadvantages of this method: it is impossible to measure large focal segments, it is impossible to measure negative systems without changing the optical scheme, high requirements for the accuracy of the system’s basing, since it is necessary to measure strictly along the optical axis.

 There is a method of measuring posterior vertex refraction of spectacle lenses [2], in which a light beam is sent from a test object (grid) to the lens and the image of the test object is observed through the telescope, achieving a sharp image of it changing the divergence of the light beam incident on the lens.

 The disadvantages of this method: for accurate measurement of the focal length, it is necessary to center the lens relative to the optical axis of the device, a long measurement time, since it is necessary to center the lens and conduct longitudinal focusing of the grid image.

=

+ Δr + r_y, (1) где Δ r - расстояние между точками, в которых измеряется фототок;
r_y - расстояние от последней поверхности оптической системы до одной из точек, где измеряются фототоки.A known method of measuring the working segment of the optical system [3], in which a light beam is directed to the optical system, measure the photocurrent at two points located at a known distance from the last surface of the optical system, and determine the magnitude of the back focal segment by the formula
S

=

+ Δr + r _y , (1) where Δ r is the distance between the points at which the photocurrent is measured;
r _y is the distance from the last surface of the optical system to one of the points where the photocurrents are measured.

 The disadvantage of this method is that it is necessary to combine the optical axis of the measured system with the axis of the light beam and know the decentration of the measured system, otherwise an error occurs due to different angles of incidence of the beam on the photodetectors, i.e., a long time for alignment of the axes and measurement error with an unknown decentration of the system.

 A known method of measuring focal lengths (zoom method) of lenses [1], in which a test object located in the focal plane of the collimator lens and illuminated by a light source through a capacitor, is projected by the measured lens into its focal plane. The image of the test object (a grid with vertical strokes) is examined using a microscope and the distance between the selected strokes of the grid is measured with an eyepiece-micrometer mounted on a microscope.

, (2) где fк - фокусное расстояние объектива коллиматора;
y - расстояние между штрихами тест-объекта.The focal length of the measured lens is determined by the formula
f ′ = f

, (2) where fк is the focal length of the collimator lens;
y is the distance between the strokes of the test object.

 The disadvantage of this method: it is impossible to measure large focal lengths, focal lengths of negative systems, long time for longitudinal focusing of the system.

 A common drawback of all of the above devices is that the device can only measure any one parameter or focal length, or focal segments of optical systems.

f $\genfrac{}{}{0ex}{}{\text{1}}{\text{2}}$ , (3) где D - размер сечения пучка, падающего на объектив;
D' - размер сечения пучка в задней фокальной плоскости вспомогательной линзы;
f₁ ² - фокусное расстояние вспомогательной линзы.The closest in technical essence to the claimed method is a method for measuring the focal lengths of lenses (Fabry-Yudin method ([4], in which a parallel beam of light with a section of a known size is directed to the measured lens, placed behind the measured auxiliary lens and, measuring the size of the beam section in the rear focal plane of the auxiliary lens, determine the focal length of the measured lens f1 by the formula
f ′ =

f $\genfrac{}{}{0ex}{}{\text{1}}{\text{2}}$ , (3) where D is the size of the cross section of the beam incident on the lens;
D 'is the size of the beam section in the rear focal plane of the auxiliary lens;
f ₁ ² is the focal length of the auxiliary lens.

+ C , в другом

- C и соответственно размер пучка в задней фокальной плоскости вспомогательной линзы от оси будет в одном направлении
D

=

· f $\genfrac{}{}{0ex}{}{\text{1}}{\text{2}}$ , в другом направлении
D

=

· f

Разность этих размеров будет
D

- D

= C

, откуда
C = f′

(4) Причем измеряемая величина фокусного расстояния не зависит от величины децентрировки, так как
D′ = D

+ D

=

f

(5)
Недостатки данного способа следующие: ограниченность диапазона измеряемых фокусных расстояний объективов, что связано с ограниченным полем зрения измерительного устройства; большее время измерения, связанное с необходимостью подбора диафрагм для каждого измеряемого фокусного расстояния, кроме того, при этом способе нельзя измерять фокальные отрезки оптических систем, если в этом возникает необходимость (например, в бинокулярных приборах нужно подбирать объективы по фокальным отрезкам и увеличению, т. е. по фокусному расстоянию) и нужно применять другие способы измерения фокальных отрезков, что опять-таки увеличивает время измерения.With this method, the decentration of the measured lens can also be measured. If the lens is decentered by the value of C, then the size of the parallel beam from the axis of the lens in one direction will be

+ C, in another

- C and, accordingly, the beam size in the rear focal plane of the auxiliary lens from the axis will be in one direction
D

=

F $\genfrac{}{}{0ex}{}{\text{1}}{\text{2}}$ in the other direction
D

=

F

The difference of these sizes will be
D

- D

= C

from where
C = f

(4) Moreover, the measured value of the focal length does not depend on the amount of decentration, since
D ′ = D

+ D

=

f

(5)
The disadvantages of this method are as follows: the limited range of the measured focal lengths of the lenses, which is associated with a limited field of view of the measuring device; longer measurement time, associated with the need to select apertures for each measured focal length, in addition, with this method it is impossible to measure the focal segments of optical systems if this is necessary (for example, binocular devices need to select lenses according to focal segments and magnification, t. i.e., by focal length) and other methods of measuring focal lengths need to be applied, which again increases the measurement time.

 The aim of the invention is to expand the range of measured focal lengths of optical systems, reducing the measurement time, and also, if necessary, measuring the focal lengths of the lenses.

(6)
-S_F =

(7)
C = f′

(8) где f₁ ² - фокусное расстояние измеряемой оптической системы;
- S_F - передний фокальный отрезок измеряемой оптической системы;
D₁', D₂' - размер сечений пучка в задней фокальной плоскости вспомогательной линзы для двух положений измеряемой оптической системы;
X₁, X₂ - расстояния от вершины передней поверхности измеряемой оптической системы до точки, в которой фокусируется сходящийся пучок света;
2 α - угол между крайними лучами сходящегося пучка лучей;
f₂' - фокусное расстояние вспомогательной линзы;
C - децентрировка измеряемой оптической системы;
(D')_A, (D')_B - размер сечения пучка света в задней фокальной плоскости вспомогательной линзы от оси вспомогательной линзы до крайнего луча пучка света, измеренные в направлении децентрировки измеряемой системы и в противоположном направлении, для одного положения измеряемой оптической системы относительно точки, в которой фокусируется сходящийся пучок света.The goal is achieved by the fact that in the method for measuring the characteristics of optical systems of focal lengths and decentration, the converging light beam is focused near the front focal plane of the auxiliary lens, the measured optical system is installed near the point at which the converging light beam is focused, and the cross-sectional size of the light beam in the rear focal plane is measured auxiliary lens, then change (in time or in space) the relative position of the point at which the converging beam of light is focused, relative to the defects of the front surface of the measured system and measure the size of the beam cross section in the rear focal plane of the auxiliary lens and, comparing the measured sizes of the cross sections, determine the required characteristic of the measured optical system using the formulas
f ′ = 2α

(6)
-S _F =

(7)
C = f

(8) where f ₁ ² is the focal length of the measured optical system;
- S _F - front focal segment of the measured optical system;
D ₁ ', D ₂ ' - the size of the cross sections of the beam in the rear focal plane of the auxiliary lens for two positions of the measured optical system;
X ₁ , X ₂ - the distance from the top of the front surface of the measured optical system to the point at which the converging beam of light is focused;
2 α is the angle between the extreme rays of a converging beam of rays;
f ₂ 'is the focal length of the auxiliary lens;
C - decentration of the measured optical system;
(D ') _A , (D') _B is the cross-sectional dimension of the light beam in the rear focal plane of the auxiliary lens from the axis of the auxiliary lens to the extreme beam of the light beam, measured in the direction of decentration of the measured system and in the opposite direction, for one position of the measured optical system relative to the point at which the converging beam of light is focused.

 The method differs from the prototype in that a converging light beam is incident on the measured optical system, in the rear focal plane of the auxiliary lens, a beam section close to parallel (collimated) is measured, beam sections are measured for two positions of the measured optical systems, in addition, this method determines an additional characteristic of the optical system - the focal segment.

 In FIG. 1 is a diagram illustrating a method for measuring the measurement characteristics of optical systems: focal lengths, focal lengths, and decentration; in FIG. 2, 3 - variants of devices on which a method for measuring the characteristics of optical systems can be implemented.

A method for measuring the characteristics of optical systems: focal lengths and decentration, in which a converging beam with an angle of 2 α between the extreme rays A and B is focused at a point F ₁ 'near the front focal plane F ₂ ' of the auxiliary lens 2.

The measured system 1 with the front focal length -f and the back-f front focal length -S _F and decentration C is set by the top of the front surface near the point F ₁ 'at a distance -X, from the top to F ₁ ' and the beam cross-section size is measured in the back focal plane of the lens 2.

)₁= -αf

- f

(9) и размер сечения пучка в плоскости от оси линзы до луча B будет
(D

)₁= -αf

+ f

(10)
Решая эти уравнения, получают
(D

)₁-(-D

) = 2f

(11) откуда децентрировка измеряемой системы будет
C = f′

(8) и далее
D

= (D

)₁+(-D

)₁= 2αf

(12)
Затем изменяют взаимное положение точки F1 и вершины передней поверхности измеряемой системы на X₂ и получают размер сечения D₂' в задней фокальной плоскости вспомогательной линзы 2
D

= - 2αf

(13)
Из (12) и (13) следует
F′ = 4αf

-S_F =

X или при симметричном расположении вершины передней поверхности оптической системы относительно т. е. F', т. е. при
X₁=-X₂=X, (14) будет
f′ = 4αf

(15)
Способ может быть реализован в устройстве (фиг. 2), в котором изменение взаимного положения точки, в которой фокусируется сходящийся пучок относительно вершины передней поверхности измеряемой линзы, происходит во времени.Based on the calculation of the paths of rays A and B, the size of the beam section in the plane F ₂ 'from the axis of the lens 2 to beam A will be
(-D

) ₁ = -αf

- f

(9) and the size of the beam cross section in the plane from the axis of the lens to beam B will be
(D

) ₁ = -αf

+ f

(10)
Solving these equations, we get
(D

) ₁ - (- D

) = 2f

(11) where will the decentration of the measured system be
C = f

(8) and further
D

= (D

) ₁ + (- D

) ₁ = 2αf

(12)
Then, the relative position of the point F1 and the vertices of the front surface of the measured system is changed to X ₂ and the section size D ₂ 'is obtained in the rear focal plane of the auxiliary lens 2
D

= - 2αf

(thirteen)
From (12) and (13) it follows
F ′ = 4αf

-S _F =

X or with a symmetrical arrangement of the vertices of the front surface of the optical system with respect to, i.e., F ', i.e., with
X ₁ = -X ₂ = X, (14) will be
f ′ = 4αf

(fifteen)
The method can be implemented in a device (Fig. 2), in which a change in the relative position of the point at which the converging beam is focused relative to the top of the front surface of the measured lens occurs in time.

 The device comprises a parallel-mounted parallel light source 4, a diaphragm 5 of size D and an optical channel in which a focusing lens 6, a base device 7, a movement mechanism 8 of the base device with a readout device 9 are installed in series and coaxially, an auxiliary lens, the front focal plane of which coincides with rear focal plane of the focusing lens, measuring device 3, for example, a photodetector array, a sensitive area that is installed in the rear A locally plane of ancillary lens.

проходит измеряемую оптическую систему 1, установленную на базировочном приспособлении 7 на известном расстоянии X₁ от вершины передней поверхности измеряемой системы до передней фокальной плоскости вспомогательной линзы 2, и вспомогательную линзу. С помощью измерительного устройства 3 измеряют размер сечения D₁' пучка лучей в задней фокальной плоскости вспомогательной линзы.A parallel light source illuminates the aperture 5 of size D and falls on the focusing lens 6 with a focal length f ₁ '. Converging beam of light with angle α =

passes the measured optical system 1 installed on the base device 7 at a known distance X ₁ from the top of the front surface of the measured system to the front focal plane of the auxiliary lens 2, and the auxiliary lens. Using the measuring device 3 measure the cross-sectional size D ₁ 'of the beam of rays in the rear focal plane of the auxiliary lens.

The base device 7 with the measured optical system is moved a certain distance along the optical axis and the reading device 9 determines the distance -X ₂ from the top of the front surface of the measured optical system to the front surface of the measured optical system to the front focal plane of the auxiliary lens 2.

Using a measuring device 3 measure the size of the beam cross section D ₂ 'in the rear focal plane of the auxiliary lens 2.

 It is desirable to place the measured optical system near the front focus of the auxiliary lens, since then a beam of rays that is close to parallel will fall on the measuring device and there will be a more contrasting spot on the measuring device (photodetector) and the measurement accuracy will be higher. Instead of the reading device 9, two stops can be installed. In this case, the movement of the base device 7 is not measured, but is fixed in the working positions on the stops.

 The method can also be implemented in a device (Fig. 3), in which a change in the relative position of the point at which the converging beam is focused relative to the top of the front surface of the measured lens occurs in space.

 The device contains sequentially mounted parallel light source 4 and two identical optical channels whose axes are parallel and offset in axial and transverse directions relative to each other, and aperture 5, focusing lens 6, auxiliary lens 2, the front focus of which coincides with the back focus of the focusing one, are coaxially mounted lenses, measuring device 3, for example, a photodetector array, a sensitive area that is located in the rear focal plane of the auxiliary lens, symmetrically to the axes beih channel and near the front focal planes of lenses arranged bazirovochnoe auxiliary device 7.

проходит измеряемую оптическую систему 1, установленную на базировочном приспособлении 7, и вспомогательную линзу 2 и падает на измерительное устройство 3.A parallel light beam from the source 4 in each channel passes through an aperture 5 of size D, the focusing lens 6 with a focal length f ₁ 'and turns into a converging one. Converging beam of light with an angle between the axis and the extreme beam α =

passes the measured optical system 1 installed on the base device 7, and the auxiliary lens 2 and falls on the measuring device 3.

Claims (2)

1. METHOD FOR MEASURING THE CHARACTERISTICS OF OPTICAL SYSTEMS: FOCUS DISTANCES AND DECENTRATION, which consists in measuring the size of the cross section of the light beam in the rear focal plane of the auxiliary lens, characterized in that before the operation of measuring the size of the cross section of the light beam in the rear focal plane of the auxiliary lens, a converging focus beam is focused near the front focal plane of the auxiliary lens the focal plane of the auxiliary lens, set the measured optical system with the top of the front surface near the point at which the converging Xia light beam then alter the mutual position of the front surface vertex of the measured optical system and the point at which the convergent light beam is focused, repeated measurement beam cross section size in the back focal plane of the auxiliary lens and the focal length determined by the formula
f ′ = 2α

,
where f ₂ ^′ is the focal length of the auxiliary lens;
2α is the angle between the extreme rays of a converging beam of light;
x ₁ , x ₂ - the distance from the top of the front surface of the measured optical system to the point at which the converging beam of light is focused;
D ₁ ^′ , D ₂ ^′ - dimensions of the sections of the light beam in the rear focal plane of the auxiliary lens, corresponding to distances x ₁ , x ₂ ,
and the focal length of the measured optical system is determined by the formula
-S _F =

,
decentration of the measured optical system is determined by the formula
C = f

,
where D _A ^′ , D _B ^′ are the dimensions of the cross sections of the light beam in the rear focal plane of the auxiliary lens from the axis of the auxiliary lens to the extreme beam of the light beam, measured in the direction of decentration of the lens and in the opposite direction at the same position of the measured system relative to the converging light beam. 2. The method according to claim 1, characterized in that, in order to simplify the processing of measurement results, take x ₂ = -x ₁ = x, and f ¹ and -S _{F are} defined as
f ′ = 4α

and -S _F =

X
3. The method according to claim 1, characterized in that the cross-sectional dimensions in the rear focal plane of the auxiliary lens are measured using an array photodetector.

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