RU2429508C1 - Apochromatic lens - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: proposed lens consists of three components arranged along ray path, first and third component being positive. First component represents meniscus lens with concave side facing image plane. Second component represents negative meniscus lens made up of biconcave and biconvex lenses glued together. Third component is made up of two approximate lenses first being biconvex and second being negative meniscus lens with concave side facing image plane. Refracting surface of lenses are spherical. Lenses are made from two optical glass grades. Lens material refractivity and mean dispersion factor obey the following relation: 1.82<n1<1.9; 1.57<n2<1.65; 21<v1<30; 60<v2<67. ^ EFFECT: reduced amount of lenses, higher relative aperture and image quality. ^ 5 dwg

Description

The invention relates to the field of optical instrumentation and can be used as an apochromatic lens in astronomical telescopes for visual observation, photo and video recording.

A known refractor system with an apochromatic corrector containing two components, the first of which is made of two lenses, and the second of the three [R. Christen in Sky and Telescope (Oct., 1985), pp.375-378].

The disadvantages of this system are the residual increase chromatism and the use of a special grade of glass.

Known apochromatic lens consisting of two components [US patent No. 4854686, 1989, Apochromat type objective lenses]. The first component consists of two lenses - a biconvex and negative meniscus, the second component is made of a biconcave lens and a positive meniscus.

The disadvantage of this lens is the presence in the first component of two lenses whose diameters are equal to the diameter of the entrance pupil, which leads to an increase in the dimensions of the lens and its mass. In addition, at least three brands of glass are used in the design of the lens.

A known apochromatic lens consisting of three components [R. Duplov, "Apochromatic telescope without anomalous dispersion glasses", Applied Optics (March 2006), 66926]. The first component is two menisci facing convex surfaces to each other, the second component is made of meniscus, biconvex and biconcave lenses, the third component is made of biconvex and biconcave lenses.

The disadvantage of this lens is the presence in the first component of two menisci whose diameters are equal to the diameter of the entrance pupil, which leads to an increase in the dimensions of the lens, its mass, complexity and the complexity of manufacturing, assembly and alignment. In addition, three grades of glass are used in the design of the lens.

The closest analogue to the claimed device by technical essence is an apochromatic lens [RF patent No. 2331094, 2008. Apochromatic lens], consisting of three components optically coupled along the rays of the rays, the first and third of which are positive, while the first component is made in the form of a single lens, the second and third components contain at least two lenses and have the shape of menisci, with the third component facing the image plane with its concave side, refracting the lens surfaces the components are spherical, the lenses are made of two brands of optical glasses. In an analog lens, the first component is a single biconvex lens. The refractive indices and dispersion coefficients of the used glass grades satisfy the condition:

1.45 <n ₁ <1.55; 1.65 <n ₂ <1.75; 50 <ν ₁ <60; 30 <ν ₂ <40.

The disadvantages of the closest analogue are the small value of the relative aperture, a large number of lenses, in addition, a narrow working spectral range from 0.44 to 0.7 μm, which is not enough for the needs of photo and video recording.

The design of the components of the closest analogue, the used glass types of the specified range of refractive indices and dispersions do not allow to reduce the number of lenses, increase the relative aperture while maintaining high image quality. The extension of the spectral range to the blue region of this system is difficult due to insufficient correction capabilities of the third component. So, the elimination of these shortcomings in the closest analogue is impossible without a significant change in the structure of the optical system.

The task to be solved by the claimed device is aimed at creating a technologically advanced apochromatic lens with high technical characteristics, which can be used in astronomical telescopes for visual observations, photo and video recording.

The technical result achieved in solving the problem is to reduce the number of lenses in the lens, increase the relative aperture when using two types of glasses as lens materials and maintain high image quality in a wide spectral range.

The problem is solved, and the technical result is achieved by the fact that the apochromatic lens consists of three components optically coupled along the rays of the rays, the first and third of which are positive. In this case, the first component is made in the form of a single lens, the second and third components contain at least two lenses and have the shape of menisci, with the third component facing the concave side to the image plane. The refractive surfaces of the component lenses are spherical, the lenses are made of two brands of optical glasses. Unlike the closest analogue, a single lens of the first component is made in the form of a meniscus, facing the concave side to the image plane. The second component is negative in the form of glued biconcave and biconvex lenses. The third component is made of two closely spaced lenses, the first of which is biconvex, the second a negative meniscus. In this case, the refractive indices and the average dispersion coefficients of the lens materials satisfy the ratio:

The execution of the first component in the form of a meniscus with the concave side facing the image plane, and the third component of two closely spaced lenses, the first of which is biconvex and the second with a negative meniscus, allows for better correction of aberrations of wide inclined beams and increase the relative aperture of the system.

The second component is negative in the form of glued biconcave and biconvex lenses and the use of glasses as materials, the refractive indices and dispersion coefficients of which satisfy relation (1), makes it possible to reduce the number of lenses and increase the relative aperture while maintaining the apochromatic correction of the system.

The combination of the proposed features allows us to solve the problem, the exclusion of any of them leads to the inability to implement an apochromatic lens with the stated technical result.

The specified solution, in our opinion, has novelty and inventive step. The authors are not aware of the optical systems of apochromatic lenses in which a combination of these features would be implemented.

The proposed invention is illustrated by the following graphic materials:

figure 1 is an optical diagram of the lens;

figure 2 is a graph of the dependence of the rear focal segment on the wavelength;

figure 3 is a graph of longitudinal axial aberrations;

4 is a graph of astigmatism and distortion;

5 is a graph of frequency contrast characteristics.

The apochromatic lens (Fig. 1) contains the first component 1, the second component 2, and the third component 3. The first component 1 is made in the form of a positive meniscus, with its concave side facing the image plane. The second component 2 is made negative in the form of glued lenses - biconcave 4 and biconvex 5. The third component 3 is made of two closely spaced lenses, the first of which is biconvex 6, the second negative meniscus 7.

All lenses are made of two grades of ordinary optical glass, the refractive indices and dispersion coefficients of which satisfy relation (1).

The action of the lens is as follows. A parallel beam of rays from a distant object passes sequentially the positive meniscus and two components and builds an image of this object in the focal plane 8. Passing through the positive meniscus 1, the beam of rays is focused, the resulting aberrations on the axis are corrected by the negative component 2. Positive component 3 corrects the field aberrations whole lens.

As a specific example, a lens with the following characteristics is designed:

focal length - 940 mm;

relative aperture - 1: 7;

working spectral range - 0.42 ÷ 0.7 μm,

the main wavelength is 0.546 microns,

angular field in the space of objects - 1.5 °;

the linear field in the image space is 24.6 mm.

Compared with the closest analogue, the relative aperture of the system is increased, the spectral range in the short-wavelength region is expanded. The manufacturability of the system is also increased: the total number of lenses is reduced from six to five, there is no three-lens gluing.

To confirm the high quality of the image provided by the proposed optical system of an apochromatic lens, the following are the characteristics most often used to evaluate image quality in optical systems of a similar purpose.

Figure 2 shows a graph of longitudinal chromatic aberration for the spectral range from 0.42 to 0.7 μm. The horizontal chromatic aberration in microns is plotted on the abscissa, and the wavelength in microns is plotted on the ordinate. The nature of the curve of longitudinal chromatic aberration indicates that in the proposed lens in the specified spectral range a high degree of correction of chromatic aberration is achieved, the value of which is 250 μm, which is less than 1/3700 of the focal length of the lens.

Figure 3 shows a graph of astigmatism of the proposed optical system of the lens. The ordinate shows the image size (in mm), and the abscissa represents astigmatic segments in mm. The residual astigmatism provided by the proposed lens at the edge of the field of view does not exceed 0.09 mm, which indicates a high degree of correction of field aberrations.

Figure 4 shows a graph of the distortion of the proposed optical system of the lens. The ordinate shows the image size (in mm), and the abscissa represents the relative distortion in%. The graph shows that the distortion at the edge of the field of view does not exceed 0.1%.

Figure 5 shows graphs of the frequency-contrast characteristics of the proposed lens. The spatial frequency in mm ^{-1 is} plotted on the abscissa axis, relative to the image plane of the lens, and on the ordinate axis, the contrast transmission coefficient in relative units. From the presented graphs it follows that the claimed apochromatic lens provides high image quality. So, with a contrast transfer coefficient of 0.1, the spatial frequency in the image plane for all image points within the field of view is at least 120 mm ^-1 . With the specified magnitude of the focal length in a specific example of execution, the angular value in the space of objects corresponding to the spatial frequency of 120 mm ^-1 is 1.8 angular seconds.

Analysis of the image quality in the example of a specific implementation confirms the high quality of the image provided by the proposed apochromatic lens over the entire field of view with an extended spectral range.

Thus, the implementation of the technical advantages of the proposed device, which has a combination of these distinguishing features, allows you to create a technologically advanced apochromatic lens with high technical characteristics, which can be used as a lens in astronomical telescopes for visual observation, photo and video recording.

Claims (1)

An apochromatic lens consisting of three components optically connected along the rays of the rays, the first and third of which are positive, the first component being a single lens, the second component having a meniscus shape, and the third component containing two lenses and facing the concave side to the plane images, the refracting surfaces of the lenses of the components are spherical, the lenses are made of two brands of optical glasses, characterized in that the single lens of the first component is made in the form of menis facing the concave side to the image plane, the second component is negative in the form of glued biconcave and biconvex lenses, the third component is made of two closely spaced lenses, the first of which is biconvex, the second negative meniscus, with refractive indices and average dispersion coefficients of lens materials satisfy the ratio:
1.82 <n ₁ <1.9; 1.57 <n ₂ <1.65; 21 <ν ₁ <30; 60 <ν ₂ <67.

Images