RU2617139C1 - Wide-angle eyepiece - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: eyepiece contains four optical components. The first negative eyepiece component from the image plane side is made as a plano-concave lens, the second positive one - as a plano-convex lens, wherein the flat surfaces of the lens face the image plane. The third positive component consists of the biconvex and plano-concave lenses glued together. The refractive gluing surface is convex to the exit pupil, and the fourth positive component consists of the negative meniscus lens and the biconvex lens glued together. The refractive gluing surface is concave to the exit pupil. The negative lenses of the first, the third and the fourth eyepiece components are made of glass such as "heavy flint". The positive lenses of the second and the third components are made of glass such as "extra-heavy crown", the positive lens of the fourth component oriented to the observer's eye, - of glass such as "heavy crown". The eyepiece has a real focus plane at the distance of about 0.17f' from the first flat surface, where mesh or crosshairs can be installed. The eyepiece has an angular view field of 76° (in the exit pupil area), the exit pupil distance from the last ophthalmic lens surface of about 0.49f' and the relative aperture of less than 1:4 with a focal length of 15-25 mm.

EFFECT: improving the image quality of the view field edge zones by reducing the residual aberrations and increasing chromaticity, decreasing the eyepiece aberrations in the exit pupil, which reduces vignetting the view field edge zones and enhances comfort when observing the objects located at the view field edges.

2 cl, 6 dwg, 1 tbl

Description

The invention relates to the field of astronomical instruments and can be used in optical systems of telescope field finders, as well as for visual observations in telescopes and astronomical binocular instruments with an increased field of view.

Known four-component scheme of the Nagler eyepiece [1]. The scheme has a real image plane and a field of view of 2ω = 76 ° -82 °, the glued components are located both on the side of the image plane and on the side of the observer's eye. However, due to the large residual astigmatism and chromatism of magnification, this scheme does not provide adequate image quality at the edges of the field of view, especially for eyepiece focal lengths exceeding 25 mm, in addition, it has significant spherical aberration in the pupil, which leads to vignetting of the edge zones field of view and creates discomfort when observing objects located at the edges of the field of view.

The prototype of the invention is a four-component wide-angle eyepiece, in which the first three components from the side of the image plane are single-lens [2]. The first component of the eyepiece is made in the form of a flat-concave lens, the second and third components are in the form of flat-convex lenses convex towards each other, and the first lens of the fourth component is biconvex and glued with a negative flat-concave lens, and the refracting surface of the fourth the component is convex to the pupil.

от первой плоской поверхности, где

- фокусное расстояние окуляра. Вынос выходного зрачка от последней плоской поверхности окуляра составляет

. Окуляр обеспечивает поле зрения 2ω=90°.The eyepiece has a real image plane located at a distance

from the first flat surface where

- the focal length of the eyepiece. The distance of the exit pupil from the last flat surface of the eyepiece is

. The eyepiece provides a field of view of 2ω = 90 °.

However, such parameters of the eyepiece, combined with good image quality at the edges of the field of view, can only be realized when the negative lenses of the eyepiece are made of glass of the "super-heavy flint" type, which practically cuts off the radiation of the blue spectral region. Therefore, the use of such eyepieces in astronomical instruments is unacceptable. When using negative lenses from glasses of the “heavy flint” type in the prototype eyepiece, a large curvature of the gluing surface of the fourth component is obtained. As a result, when correcting the chromatism of the increase at the field edge, its value in the middle part remains significant, in addition, the residual aberrations at the field edges and spherical aberration in the pupil of the eyepiece increase, which leads to a significant deterioration in image quality and discomfort of observation at the edges of the field of view.

The task of the invention is to improve image quality at the edge of the field of view and reduce spherical aberration of the eyepiece in the exit pupil. At the same time, glasses passing through the entire spectrum of the visible radiation should be used for the components of the eyepiece, and the removal of the exit pupil of the eyepiece and the position of the image plane should not cause discomfort to the observer and enable convenient placement of a grid with a crosshair in the image plane.

The technical result of the invention is the creation of an eyepiece with improved image quality at the edge of the field of view and less spherical aberrations of the eyepiece in the exit pupil.

This result is achieved in that in the scheme of a wide-angle eyepiece containing four components, the first of which is made in the form of a flat-concave lens, and the second is in the form of a flat-convex lens, the flat surfaces of the lenses facing the image plane, the third positive component consists of glued together biconvex and flat-concave lenses, and the refracting surface of the gluing convex to the exit pupil, and the fourth positive component consists of a negative meniscus glued together new lens and biconvex lens, while the refracting surface of the gluing is turned concavity to the exit pupil. The lenses of the third positive component are made of glass with approximately equal refractive indices for the main line of the spectrum, but with different dispersions.

The implementation of the third positive component of the eyepiece in the form of positive biconvex and negative flat-concave lenses glued together with approximately equal refractive indices for the main line of the spectrum, but with different dispersions, makes it possible to reduce the residual chromatism of the increase in the field of view, since it allows introducing one negative lens and thereby reduce the curvature of the refracting bonded surface of the fourth component.

The reversal of the refractive surface of the gluing of the third component by the convexity to the exit pupil and, in contrast to the prototype, the reverse alternation of the optical forces of the lenses of the fourth component, composed of a negative meniscus lens glued together and a biconvex lens with a refractive surface of the gluing facing concavity to the exit pupil, allows to reduce the angles incidence and refraction of rays passing through the refracting surfaces of the lenses. This causes a decrease in the residual chromaticity of the increase, as well as a decrease in the residual field aberrations and spherical aberration of the eyepiece in the exit pupil, which ultimately leads to improved image quality and increased comfort of observation of the edge zones of the field of view.

The applicant has not identified technical solutions having features that match the distinctive features of the invention. A wide-angle eyepiece of four components with the claimed combination of essential features in known sources of information is also not found.

The proposed invention is illustrated by the following graphic materials:

FIG. 1 is an optical diagram of a wide-angle eyepiece.

FIG. 2 is a graph of the chromatism of the magnification of the eyepiece.

FIG. 3 - graphs of residual axial aberrations of the eyepiece:

a) longitudinal;

b) transverse:

c) wave;

d) deviation from the law of sinuses.

FIG. 4 - graphs of field aberrations:

a) distortion;

b) the course of astigmatic focal surfaces in the meridional section.

FIG. 5 - graphs of angular aberrations in the field of view:

a) in the meridional plane;

b) in the sagittal plane.

FIG. 6 is a graph of transverse spherical aberration of the main rays of the eyepiece.

In FIG. 1 shows the proposed optical scheme of the wide-angle eyepiece.

The eyepiece contains four components, the first of which is made in the form of a flat-concave lens 1, and the second is in the form of a flat-convex lens 2, with the flat surfaces of the lenses facing the image plane. The third positive component 3 consists of biconvex and flat-concave lenses glued together, the refracting surface of the gluing convex to the exit pupil, and the fourth positive component 4 consists of negative meniscus lenses glued together and the biconvex lens, while the refracting surface of the gluing is concave to the exit pupil.

Quasi-telecentric beams of light rays coming from the image plane formed by the previous optical system are scattered by the negative lens 1 and focused by the system of positive components 2 and 3 into the front focal plane of the positive component 4, after which they are parallel to the beam of rays and are collected in the plane of the exit pupil of the eyepiece.

We will justify the possibility of achieving the claimed technical characteristics in the proposed scheme.

The reason for the low image quality at the edges of the field of view and significant spherical aberration of the main rays of the field beams in the exit pupil of the prototype eyepiece is because the fourth component has a large curvature of the gluing surface (provided that the negative lenses of the eyepiece are made from a heavy flint that transmits the radiation of the entire visible spectrum) and its orientation relative to the exit pupil, causing large residual aberrations. To improve the image quality of the edge zones of the field of view associated with the presence of residual astigmatism and increase chromatism, as well as reduce the spherical aberration of the main rays of the eyepiece in the exit pupil, it is necessary to reduce the curvature of the glued surface of the positive fourth component. This can be done by distributing the negative optical power of the eyepiece lenses not between two lenses, as in the prototype, but between three, by performing a positive component 3 of biconvex and flat-concave lenses glued together, and for reasons of reducing residual field aberrations, the refractive surface of the gluing should be reversed bulge to the exit pupil. The refractive surface of the gluing of the fourth component for the same reasons must be turned concavity to the exit pupil. Such an arrangement of the refracting glued surfaces of components 3 and 4 provides minimal incidence and refraction angles of the main rays on these components of the circuit, which leads to a decrease in residual field aberrations. Thus, the fourth positive component of the eyepiece will have the opposite, relative to the prototype, orientation of the lenses and their shape: the first lens, negative, has the shape of a meniscus, and the second, positive, is biconvex.

, заданную параметрами (1). В сноске параметров (1): r_s - радиусы сферических поверхностей по порядку следования в схеме, начиная от плоскости изображения (s - номер поверхности); d_s - толщины линз и воздушные промежутки; n_s - показатели преломления среды, указаны для линии спектра

(546,07 нм). Для преломляющих сред указаны марки стекла; ∅_S - диаметры оптических поверхностей;

- фокусное расстояние окуляра для линии e; S_F - положение плоскости изображения от первой плоской поверхности компонента 1;

- положение выходного зрачка от последней поверхности окуляра.As a specific example, confirming the validity of the connection of the considered distinguishing features with the achievement of the claimed technical results, we consider the optical scheme of the proposed wide-angle eyepiece with a focal length

defined by parameters (1). In the footnote of parameters (1): r _s are the radii of the spherical surfaces in the order in the diagram, starting from the image plane (s is the surface number); d _s - thickness of the lenses and air gaps; n _s are the refractive indices of the medium indicated for the spectrum line

(546.07 nm). For refractive media, glass grades are indicated; ∅ _S are the diameters of the optical surfaces;

- the focal length of the eyepiece for line e; S _F is the position of the image plane from the first flat surface of component 1;

- the position of the exit pupil from the last surface of the eyepiece.

Table 1 shows the focal lengths of the circuit components and their constituent lenses.

и

, практически не создают дискомфорта при наблюдении с такими окулярами при фокусном расстоянии от 15 до 25 мм. Перефокусировка окуляра при наводке на резкость перекрестия сетки (в визуальном искателе) возможна в диапазоне ± 5 диоптрий. При этом для близорукого наблюдателя между плоскостью штрихов сетки и первой плоской поверхностью линзы остается еще достаточный воздушный промежуток.The exit pupil of the eyepiece is not more than 6 mm. The angular field in the space of the exit pupil is ω _{y, z} = ± 38 °. Negative lenses of the circuit are made of TF4 glass, positive lenses of components 2 and 3 are made of STK19 glass. These glasses have almost the same refractive index for the main line of the spectrum e . The positive lens of component 4 is made of TK14 glass (GOST 3514-94). The distances from the image plane to the first surface of the lens block of the eyepiece and from the last surface of the lens block to the exit pupil, respectively

and

practically do not create discomfort when observing with such eyepieces at a focal length of 15 to 25 mm. Refocusing the eyepiece when aiming at the sharpness of the crosshair of the grid (in the visual finder) is possible in the range of ± 5 diopters. At the same time, for the nearsighted observer, there is still a sufficient air gap between the grid line plane and the first flat surface of the lens.

From the data of the footnote of parameters (1) and table 1 it can be seen that the first negative component of the eyepiece is made in the form of a flat-concave lens. The second positive component of the eyepiece is made in the form of a plano-convex lens, with the flat surfaces of the lenses facing the image plane. The third positive component consists of biconvex and flat-concave lenses glued together, the refractive chromatic surface of the gluing convex to the exit pupil, and the focal lengths of the second and third components are almost equal. The fourth positive component consists of a negative meniscus lens glued together and a biconvex lens, the refracting surface of the gluing facing the exit pupil with a concavity.

Consider what this combination of distinctive features leads to.

In FIG. 2 shows a graph of the chromatism of the magnification of the eyepiece. The ordinate shows the field angle ω in the area of the exit pupil, expressed in degrees. The abscissa shows the values of the increase in chromatism calculated by the formula:

- расстояние от точки пересечения главного луча с плоскостью изображения до оптической оси, вычисляемое в обратном ходе лучей со стороны выходного зрачка. Из графика видно, что хроматизм увеличения окуляра небольшой и по полю зрения 2ω=76° в области выходного зрачка изменяется в пределах ±0,3%.expressed as a percentage.

- the distance from the point of intersection of the main beam with the image plane to the optical axis, calculated in the reverse direction of the rays from the exit pupil. The graph shows that the chromatism of the magnification of the eyepiece is small and in the field of view 2ω = 76 ° in the area of the exit pupil varies within ± 0.3%.

In FIG. 3 shows graphs of the residual axial aberrations of the eyepiece.

(546,07 нм), F (486,1 нм) и C (656,3 нм). По оси абсцисс отложены значения координаты m на выходном зрачке. По оси ординат на графике фиг. 3a отложены значения продольной сферической аберрации ΔS' в мм, на графике фиг. 3б отложены значения поперечной сферической аберрации dY' мм, на графике фиг. 3в отложены значения волновой сферической аберрации W, выраженной в долях длины волны своего цвета, на графике фиг. 3г показано отступление от закона синусов Eta, %, характеризующее исправление комы окуляра.The graphs are plotted in the reverse direction of a parallel beam of rays from the exit pupil side for three lines of the visible spectrum corresponding to wavelengths

(546.07 nm), F (486.1 nm) and C (656.3 nm). The abscissa shows the values of the coordinate m on the exit pupil. The ordinate axis in the graph of FIG. 3a, the longitudinal spherical aberration ΔS 'in mm is plotted, in the graph of FIG. 3b, the lateral spherical aberration values dY ′ mm are plotted, in the graph of FIG. 3c, the values of the wave spherical aberration W, expressed in fractions of the wavelength of its color, are plotted in the graph of FIG. 3d shows a deviation from the law of sinuses Eta,%, characterizing the correction of the coma of the eyepiece.

From the graphs of the residual axial aberrations of the eyepiece (Fig. 3) it follows that the residual spherical aberration on the axis of the eyepiece is quite well corrected and with a full eye pupil diameter of 6 mm, which corresponds to a relative aperture of the eyepiece of the order of 1: 4, does not exceed 0.2λ, and the residual wave aberrations in the F-С spectral range do not go beyond 0.75λ. The deviation from the law of sinuses is relatively small and does not exceed 0.13%.

(546,07 нм).In FIG. Figure 4 shows the graphs of the residual field aberrations of the eyepiece constructed for the backward ray path from the exit pupil in the spectral line

(546.07 nm).

The abscissa shows the field angle ω _y in the area of the exit pupil, expressed in degrees. The ordinate axis in the graph of FIG. 4a, the values of the relative distortion D, expressed in%, are plotted. The ordinate axis in the graph of FIG. 4b, the course of astigmatic focal surfaces of the eyepiece x ' _{m is given} ; x ' _s in the meridional section of the circuit, expressed in mm. The dashed line indicates the course of the focal surface for sagittal rays, and the solid line for meridional rays.

не превышает 1,1 мм.From the graphs of FIG. Figure 4 shows that the relative distortion of the eyepiece at the edge of the field 2ω = 76 ° does not exceed 13.9%. Astigmatism is also corrected somewhat better and at the edge of the field 2ω = 76 °

does not exceed 1.1 mm.

, C, F. Кривые сагиттального сечения выделены штриховой линией. Над каждым рядом графиков указаны линейные координаты y, выраженные в мм, точки поля изображения, соответствующей углу поля в области выходного зрачка ω_y=0°, 20° и 38°.To finally characterize the image quality of the proposed wide-angle eyepiece, telecentric beams of rays were formed that extend from the side of the image plane (Fig. 1), and angular aberration plots were plotted for three zones of the eyepiece field of view corresponding to the inclination of the main ray relative to the axis of the scheme: ω = 0 °; ω = 20 °; ω = 38 ° (Fig. 5). Graphs 5a correspond to the meridional section of the beam of rays. The tangents of the angle of the main ray in the meridional plane tgσ _{y are} plotted along the abscissa. Graphs 5b correspond to the sagittal section of the beam of rays. The tangents of the angle of the main ray in the sagittal plane tgσ _{z are} plotted along the abscissa. On the ordinate axis, angular aberrations dW _{y 'are} plotted on all graphs; dW _{z '} corresponding to the tangents of the principal rays tgσ _{y, z} , expressed in angular minutes. The value of tgσ _max = 0.125 corresponds to half of the maximum relative aperture of the eyepiece 1: 4 (it can be seen that for this aperture value the eyepiece has a small vignetting of the edge beam, not exceeding 20%, which is reflected in the asymmetry of the lower graph 5a). Graphs plotted for three spectrum lines

, C, F. Sagittal section curves are indicated by a dashed line. Above each row of graphs, the linear coordinates y, expressed in mm, of the image field point corresponding to the field angle in the exit pupil region ω _y = 0 °, 20 ° and 38 ° are indicated.

Graphs of angular aberrations by the field of view characterize the aggregate (of all aberrations) image quality of a separate zone of the field of view of the proposed eyepiece, expressed in angular minutes in the area of the exit pupil of the eyepiece, and therefore in the pupil of the eye of the observer.

It is known that the average observer in the area of the pupil of the eye with a diameter of 5 mm near the zone of best vision has an angular resolution of the eye of about 3.7 ', and with the pupil of the eye with a diameter of 6 mm or more, the resolution of the eye decreases significantly [3]. This should be considered when evaluating the image quality of the eyepiece. From the graphs it follows that on the axis the angular aberrations of the eyepiece at a maximum relative aperture of 1: 4 in the entire visible range of the spectrum fit into a value of about 4 ', which, in principle, is less than the resolution of the eye on the pupil of 6 mm. For a relative aperture of 1: 8, the angular aberrations on the axis decrease to a very insignificant component of 1.2 ', which is 2.3 times less than the resolution of the eye with a pupil diameter of 3 mm. On the angular field of the eyepiece ω = ± 20 °, which the eye covers from one installation without rotation, the image quality at a relative aperture of 1: 4 deteriorates to 22.5 '. With a relative aperture of 1: 8 in the field 2ω = ± 20 °, the angular aberrations of the proposed scheme do not go beyond 7.5 ', which is 2.7 times higher than the average resolution of the eye for a pupil with a diameter of 3 mm [3]. As for the edge of the maximum field of view 2ω = ± 38 °, the angular aberrations of the proposed wide-angle eyepiece scheme and the prototype scheme are quite comparable if the negative lenses of the prototype are made of STF11 glass (super-heavy flint). But, as already mentioned, this glass is unsuitable for developing astronomical eyepieces based on it, since it practically cuts off the blue region of the spectrum and changes the color rendering in the image of the object. If the lenses of the prototype eyepiece are made of ordinary heavy flint, then the angular aberrations at the edge of the field of view will significantly (several times) increase relative to the proposed eyepiece scheme.

поперечной сферической аберрации луча в плоскости выходного зрачка, выраженное в мм. По оси абсцисс отложены значения углов ω главного луча с оптической осью окуляра в плоскости выходного зрачка, выраженные в градусах. Из графика фиг. 6 видно, что поперечное смещение главных лучей в плоскости выходного зрачка не превышает 0,32 мм. Это практически исключает виньетирование зрачком глаза краевых зон поля зрения и тем самым обеспечивает комфорт наблюдения.In FIG. 6 is a graph of the spherical aberration of the main rays of the eyepiece. A telecentric ray path in the image space is assumed. The y-axis is plotted

transverse spherical beam aberration in the plane of the exit pupil, expressed in mm. The abscissa axis represents the angles ω of the main beam with the optical axis of the eyepiece in the plane of the exit pupil, expressed in degrees. From the graph of FIG. Figure 6 shows that the transverse displacement of the main rays in the plane of the exit pupil does not exceed 0.32 mm. This practically excludes vignetting by the pupil of the eye of the marginal zones of the field of view and thereby ensures comfort of observation.

Thus, the proposed scheme of the wide-angle eyepiece provides the best image quality at the edge of the field of view and provides better viewing comfort with respect to the prototype eyepiece scheme comparable in technical capabilities.

This is ensured by the presence of a new set of distinctive features:

1. The third positive component consists of biconvex and flat-concave lenses glued together, and the refracting surface of the gluing is convex to the exit pupil;

2. The fourth positive component consists of a negative meniscus lens glued together and a biconvex lens, the refracting surface of the gluing facing the exit pupil with a concavity.

Thus, the proposed scheme of the wide-angle eyepiece provides the best image quality of objects in relation to the four-component scheme of the prototype eyepiece comparable in technical capabilities and provides the best observation comfort with respect to it. This makes it possible to apply it in wide-angle field finders of telescopes containing a grid with a crosshair marking the center of the field of view, as well as for visual observations in telescopes and astronomical binocular devices with an increased field of view.

LITERATURE

1. Patent US 4,525,035. Wide angle eyepiece / A. Nagler. 1985.

2. A.c. USSR 572741 / Wide-angle eyepiece / M.M. Rusinov, E.H. Goncharenko, G.N. Repinsky.

3. Maksutov D. D. Astronomical Optics: 2nd ed. / ed. N.N. Michelson. L .: Nauka, 1979. - p. 160.

Claims (2)

1. A wide-angle eyepiece containing four components, the first of which is made in the form of a flat-concave lens, and the second is in the form of a flat-convex lens, the flat surfaces of the lenses facing the image plane, characterized in that the third positive component consists of glued between a biconvex and flat-concave lenses, the refracting surface of the gluing convex to the exit pupil, and the fourth positive component consists of a negative meniscus lens and a biconvex glued together lens, while the refracting surface of the gluing is turned concavity to the exit pupil. 2. A wide-angle eyepiece according to claim 1, characterized in that the lenses of the third positive component are made of glass with approximately equal refractive indices for the main line of the spectrum, but with different dispersions.

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