RU2433432C2 - Apochromatic lens (versions) - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: lens consists of three components. The first component is a single biconvex lens (1). The second consists of a biconvex (2) and a biconcave (3) lens and a converging-meniscus lens (4). The third consists of a biconvex (5) and a biconcave (6) lens. All the lenses are made from two types of common optical glass. In the first version, refraction indices 1.45<n₁<1.55; 1.65<n₂<1.75, and dispersion coefficients 60<γ₁<95; 20<γ₂<30 or 40<γ₂<50. In the second version, refraction indices and dispersion coefficients satisfy the condition: 1.43<n₁<1.45 or 1.55<n₁<1.65; 1.75<n₂<2.2; 60<γ₁<95; 20<γ₂<30 or 40<γ₂<50.

EFFECT: higher image quality.

2 cl, 9 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.

The well-known 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 complexity of manufacturing, assembly and alignment. In addition, three grades of glass are used in the design of the analog lens.

The closest technical solution adopted for the prototype is an apochromatic lens containing three components (Apochromatic lens. Patent RU 2331094, priority date 06/08/2006). The first component is a single biconvex lens, the second consists of three lenses - a biconvex, biconcave, and positive meniscus, and the third component consists of a biconvex and biconcave 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.

However, such a lens has insufficient image quality due to the fact that the glasses used have fairly close refractive indices and dispersion coefficients.

The objective of the invention is the creation of an apochromatic lens with higher image quality.

The problem is achieved in that in an apochromatic lens containing three positive components, the first of which is a single biconvex lens, the second consists of three lenses - biconvex, biconcave and positive meniscus, the third component consists of biconvex and biconcave lenses, all lenses are made of two grades of ordinary optical glass, the refractive indices of which are 1.45 <n ₁ <1.55; 1.65 <n ₂ <1.75, in contrast to the known dispersion coefficients satisfy the condition 60 <γ ₁ <95; 20 <γ ₂ <30 or 40 <γ ₂ <50.

The second variant of the proposed apochromatic lens is characterized in that the lenses are made of two grades of ordinary optical glass with a refractive index of 1.43 <n ₁ <1.45 or 1.55 <n ₁ <1.65; 1.75 <n ₂ <2.2 and dispersion coefficients 60 <γ ₁ <95; 20 <γ ₂ <30 or 40 <γ ₂ <50.

The invention is illustrated by the following graphic materials:

figure 1 - Optical diagram of the lens,

figure 2 - Graph of the rear focal segment on the wavelength,

figure 3 is a graph of the dependence of the rear focal segment on the wavelength of the prototype,

figure 4 - Graph of astigmatism,

5 is a graph of the astigmatism of the prototype,

6 is a graph of distortion,

Fig.7 is a graph of the distortion of the prototype,

Fig. 8 is a graph of a frequency-contrast characteristic,

Fig.9 is a graph of the frequency-contrast characteristics of the prototype.

The optical scheme of the apochromatic lens is shown in Fig. 1, it 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 lenses 6. 7 - the focal plane.

All lenses are made of two brands of 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; 60 <γ ₁ <95; 20 <γ ₂ <30 or 40 <γ ₂ <50.

The second variant of the proposed apochromatic lens is characterized in that the lenses are made of two grades of ordinary optical glass with a refractive index of 1.43 <n ₁ <1.45 or 1.55 <n ₁ <1.65; 1.75 <n ₂ <2.2 and dispersion coefficients 60 <γ ₁ <95; 20 <y ₂ <30 or 40 <γ ₂ <50.

Apochromatic lens works as follows. 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 ΔS '(μm). The ordinate shows the wavelength λ (μm).

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

Figure 4 shows a graph of astigmatism, and figure 6 is a graph of the distortion of the proposed optical system apochromatic lens. The ordinate axes on both graphs show the image size Y '(mm). In Fig. 4, the abscissa shows the astigmatic segments Z ' _s , Z' _m (mm), and Fig. 6 shows the relative distortion in Δy 'in%.

On Fig shows graphs of the frequency-contrast characteristics of the proposed apochromatic lens. The spatial frequency N mm ^{-1 is} plotted on the abscissa axis, referred to the image plane of the lens, and on the ordinate axis is the contrast transmission coefficient in relative units.

From the graphs of the claimed apochromatic lens and prototype, it is obvious that the claimed apochromatic lens has higher performance in terms of image quality over the field of view. A better image was obtained due to the fact that glasses with a significant difference in refractive indices and dispersion coefficients were used.

As an example, a prototype is made, the material for 1, 3, 5 elements of the optical scheme of which is glass with a refractive index n ₂ and a dispersion coefficient of γ ₂ , and for 2, 4, 6 elements of the optical scheme, with a refractive index of n ₁ and a dispersion coefficient γ ₁ .

The lens has the following characteristics:

focal length - 940 mm

relative aperture - 1: 7.5

working spectral range - 0.44: 0.7 μm

the main wavelength is 0.546 microns

angular field of view in the space of objects - 1.5 °

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

Claims (2)

1. Apochromatic lens containing three components, the first of which is a single biconvex lens, the second consists of a biconvex and biconcave lenses and a positive meniscus, the third is a biconvex and biconcave lenses, all lenses are made of two grades of ordinary optical glass with refractive indices 1.45 <n ₁ <1.55; 1.65 <n ₂ <1.75, characterized in that the dispersion coefficients of the glasses used satisfy the condition:
60 <γ ₁ <95;
20 <γ ₂ <30 or 40 <γ ₂ <50. 2. Apochromatic lens containing three components, the first of which is a single biconvex lens, the second consists of a biconvex and biconcave lenses and a positive meniscus, the third is a biconvex and biconcave lenses, and all lenses are made of two grades of ordinary optical glass, characterized in that the refractive indices and dispersion coefficients of the glasses used satisfy the condition:
1.43 <n ₁ <1.45 or 1.55 <n ₁ <1.65;
1.75 <n ₂ <2.2;
60 <γ ₁ <95;
20 <γ ₂ <30 or 40 <γ ₂ <50.

Images