RU2331094C2 - Apochromatic objective - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: apochromatic objective can be used in astronomical telescopes for visual observation and photographing. The objective consists of three components, the first of which is a single biconvex lens; the second component consists of three lenses - biconvex, biconcave and a converging meniscus; the third component consists of a biconvex and biconcave lens. All lenses are made from two types of conventional optical glass, refraction coefficients and dispersion coefficients of which satisfy the condition: 1.45<n₁<1.55, 1.65<n₂<1.75, 50<γ₁<60, 30<γ₂<40.

EFFECT: making of an apochromatic objective with high quality of image with minimum number of optical elements when using conventional optical glass for making the lenses.

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 and photographing.

Known dialysis refractor Alexander Rogers, consisting of two components [A. Rogers, "On the Construction of large Achromatic Telescopes," Memoirs of the Astronomical Society of London 3.2 (1829), pp.229-233]. The first component is a plano-convex lens, the second component is made of two lenses and serves to correct spherical aberration and achromatization of the system.

The disadvantages of Alexander Rogers dialysis refractor are residual secondary spectrum and increase chromatism.

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

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

The closest technical solution adopted for the prototype is the Roman Duplov system, consisting of three components [R. Duplov, "Apochromatic telescope without anomalous dispersion glasses", Applied Optics (March 2006), 66926]. The first component is two meniscus, convex to each other, the second component is made of meniscus, biconvex and biconcave lenses, the third component is made of biconvex and biconcave lenses.

However, such a lens has two overall meniscus in the first component, 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 prototype lens.

The objective of the invention is the creation of an apochromatic lens with high image quality with a minimum number of optical elements when using ordinary optical glass as a lens material.

The problem is achieved in that in an apochromatic lens containing three positive components, the component consisting of three lenses - biconvex, biconcave and positive meniscus, and the third component consists of biconvex and biconcave lenses, the first component is made in the form of a biconvex lens, all lenses are made of two grades of ordinary optical glass, the refractive indices and dispersion coefficients of which satisfy the condition:

1.45 <n ₁ <1.55

1.65 <n ₂ <1.75

50 <γ ₁ <60

30 <γ ₂ <40

The invention is illustrated by the following graphic materials:

Figure 1 - Optical diagram of the lens.

Figure 2 is a graph of the dependence of the rear focal segment on the wavelength.

Figure 3 - Graph of longitudinal axial aberrations.

Figure 4 - Graph of astigmatism and distortion.

Figure 5 - Graph of the frequency-contrast characteristics.

The apochromatic lens contains two positive components and an additional biconvex lens 1. The first positive component consists of glued biconvex lens 2, a biconcave lens 3 and a positive meniscus 4. The second positive component consists of glued biconvex lens 5 and a biconcave lens 6.

All lenses are made of two grades of ordinary optical glass, the refractive indices and dispersion coefficients of which satisfy the condition:

1.45 <n ₁ <1.55

1.65 <n ₂ <1.75

50 <γ ₁ <60

30 <γ ₂ <40

A parallel beam of rays from a distant object passes sequentially a biconvex lens and two components and builds an image of this object in the focal plane 7. Passing through a biconvex lens 1, the beam is collimated, the aberrations arising on the axis are corrected by the first component. The second component corrects the field aberrations of the entire lens.

When calculating the apochromatic lens, the authors proceeded from the fact that the main power optical element is a single biconvex lens of a large aperture, the first positive component corrects aberrations on the axis, and the second positive component corrects field aberrations.

Figure 2 shows the dependence of the rear focal segment of the lens on the wavelength. The abscissa shows the difference between the value of the focal length for a wavelength of 0.546 μm and the values of the focal lengths for wavelengths in the range 0.43-0.67 μm (dimension in μm). The ordinate shows the wavelength (μm).

The S-shaped curve characteristic of apochromats is clearly visible.

Figure 3 shows graphs of the longitudinal axial aberrations of the proposed lens. On the abscissa axis, the values of longitudinal aberrations in microns are plotted, and on the ordinate axis, the coordinate in the plane of the entrance pupil (in microns).

Figure 4 shows graphs of astigmatism (left) and distortion (right) of the proposed optical system of the lens. The ordinate axes in both graphs show the image size (in mm), and the abscissa axis shows the astigmatic segments in mm and the relative distortion in%.

Figure 5 shows graphs of the frequency-contrast characteristics of the proposed lens. The spatial frequency in mm, relative to the plane of the image of the lens, is plotted along the abscissa axis, and the contrast transmission coefficient in relative units along the ordinate axis.

From the above graphs it can be seen that the proposed apochromatic lens has higher performance in terms of the quality of the image given over the field of view.

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

focal length - 960 mm

relative aperture - 1: 7.7

working spectral range - 0.44: 0.7 μm

the main wavelength is 0.546 microns

1.5 angular field of view in the space of objects

linear field of view in the image space is 24 mm.

Claims (1)

Apochromatic lens containing three components, the second of which consists of a biconvex and biconcave lenses and a positive meniscus, the third of a biconvex and biconcave lenses, characterized in that the first component is a single biconvex lens, the lenses are made of two brands of optical glass, refractive indices and dispersion coefficients which satisfy the condition 1.45 <n ₁ <1.55, 1.65 <n ₂ <1.75, 50 <γ ₁ <60, 30 <γ ₂ <40.

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