RU2582207C1 - Double lens - Google Patents

Abstract

FIELD: photography.

SUBSTANCE: lens consists of, located on beam path, a negative meniscus whose convex side faces object, and a biconvex lens, with ratios: 2,0 < R₁/R₂ < 3,0;

0,9<R₂/R₃<1,1; d₂/f′ < 0,002;

where R₁, R₂, R₃, R₄ - radii of first, second, third and fourth surfaces lenses on beam path, respectively; d₂ - air gap between lenses; f′ is focal distance; ν₁ and ν₂ - dispersion coefficients of glass of first and second lenses respectively; p₁ and p₂ - relative partial dispersion glass of first and second lenses respectively.

EFFECT: technical result is increase in focal length while maintaining high quality of image, improving performance by reducing temperature equalisation time of objective lens with ambient temperature, improving manufacturability.

2 cl, 1 dwg, 2 tbl

Description

The invention relates to optical instrumentation and can be used in various optical systems, in particular in astronomical telescopes, collimators and similar systems.

Known two-lens (RF patent No. 2384868 C1, publ. March 20, 2010), consisting of located along the beam of a biconvex lens and a negative meniscus, convex to the image, for which the following relations are true:

1.41 <n ₁ <1.619;

1.54 <n ₂ <1.79,

where R ₁ , R ₂ , R ₃ are the radii of the first, second and third optical surfaces; n ₁ , n ₂ are the refractive indices of the material of the first and second lenses for line e. The lens has a focal length in the range of 899.84-1002.45 mm, which is not always sufficient for a number of applications (for example, in astronomical telescopes).

Known two-lens (RF patent No. 32892 U1, publ. 09/27/2003), consisting of located along the beam of a negative lens with a first aspherical surface and a positive lens, for which the following relations are true:

φ ₁ = (2-3) φ _OB ;

φ ₂ = (3-4) φ _OB ,

where φ ₁ , φ ₂ , φ _OB are the optical powers of the first, second lenses and lens, respectively, while the air gap between the lenses is a sufficiently large value equal to (0.003-0.01) / φ _OB .

Asphericity of the first surface of the lens makes it complex and low-tech.

The closest analogue to the claimed technical solution is a two-lens lens (Japanese application 1994000271872, publ. 04/30/1996), consisting of a negative meniscus located along the beam convex to the subject and a biconvex lens with spherical surfaces, for which the following relations are true:

0.8 <R _l / R ₂ <2.0;

0.6 <R ₁ / R ₄ <2.0;

0.2 <d ₂ / f ′ <1.0,

where d ₂ is the air gap between the lenses; f ′ is the focal length of the lens.

The lens provides good aberration correction only at very small focal lengths (of the order of 1 mm), which is clearly not enough for

The objective of the invention is to increase the technical and operational characteristics of the lens, as well as improving manufacturability. use, for example, as a telescope or collimator lens.

The problem is solved in that in a two-lens lens, consisting of a negative meniscus convex towards the subject and a biconvex lens located along the rays, in contrast to the known one, the following relationships take place:

2.0 <R ₁ / R ₂ <3.0;

0.9 <R ₂ / R ₃ <1.1;

d ₂ / f ′ <0.002,

where R ₁ , R ₂ , R ₃ , R ₄ are the radii of the surfaces of the lenses of the lens; d ₂ - the air gap between the lenses; f ′ is the focal length of the lens; ν ₁ and ν ₂ are the dispersion coefficients of the glass of the first and second lenses of the lens, respectively; p ₁ and p ₂ are the relative partial dispersions of the glass of the first and second lenses of the lens, respectively.

It is advisable to make the radii of the second and third surfaces R ₂ and R ₃ concentric.

Application of the above ratios of radii of curvature, in combination with the ratio of the optical constants of materials (dispersion coefficients and relative partial dispersions) of lenses? along with monochromatic aberrations of the lens, it allows minimizing position chromatism and the secondary spectrum, which improves the main technical characteristic - increases the focal length (by 20-30% compared with the analogue - RF patent No. 2384868 C1) while ensuring high image quality. The air gap between the lenses, which is small in relation to the focal length, provides a reduction in the time when the temperature of the lens aligns with the ambient temperature. The execution of all surfaces of the lenses is spherical and the proximity of the radii of the second and third surfaces increases manufacturability.

The drawing shows an optical diagram of the lens.

The lens consists of the negative meniscus 1 located along the rays, convex to the object, and a biconvex lens 2. Lenses 1 and 2 are made of optical glass and have spherical surfaces.

One of the possible technical implementations of the lens (design parameters of the first lens design) in accordance with the proposed solution is shown in table 1, where ν_e - glass dispersion coefficient; p_F′-e - relative partial dispersion of glass; n_g, n_{F ′}, n_e, n_{C ′}, are the refractive indices of glass for the lines g, F ′, e, C ′, respectively.

Characteristics of the calculated lens:

- diameter of the entrance pupil 152 mm;

- focal length 1200.2 mm;

- relative aperture 1: 8;

- angle of view 1 °.

The lens is fixed for the visible region of the spectrum and can be used, for example, as the lens of an astronomical telescope, a collimator lens, or in other devices where a good correction of aberrations is required, especially near the optical axis.

In the lens there are relations:

R ₁ / R ₂ = 2.17, i.e. is within the declared limits of 2.0 ... 3.0;

т.е. меньше 0,08;

those. less than 0.08;

R ₂ / R ₃ = 1.011, i.e. is within the declared range of 0.9 ... 1.1;

d ₂ / f ′ = 0.0004, i.e. less than 0.002;

т.е. больше 34;

those. more than 34;

т.е. меньше 0,001.

those. less than 0.001.

In the proposed scheme, the secondary spectrum is minimized, which can significantly increase the focal length of the lens. This is necessary, in particular, for use in astronomical telescopes.

So, at a point on the axis of the system in a single installation plane, the wave aberration has the following values (in wavelengths λ):

- for the line g - 0.636 λ;

- for the line F ′ - 0.239 λ;

- for the line e - 0,035 λ;

- for the line C ′ - 0,201 λ,

which provides high image quality.

The small air gap allows to minimize the air volume between the lenses of the lens, therefore, in the telescope tube, where the first lens has direct contact with the surrounding air and the second is insulated, the temperature equalization of the lenses occurs faster with a smaller thickness of the air layer, which is an insulator.

Since one of the lenses is made of a material less resistant to a humid atmosphere (for example, OK4 glass was used for the second lens), the selected configuration of the circuit in which this material is used for the second lens along the rays makes it easier to isolate it from the lens when used in a telescope the harmful effects of environmental humidity, since on the one hand it is protected by the first lens, and on the second by the telescope tube.

Another possible technical implementation of the lens in accordance with the proposed solution is shown in table 2, which presents the design parameters of the second lens design.

The characteristics of the calculated second lens design are the same:

- diameter of the entrance pupil 152 mm;

- focal length 1200.2 mm;

- relative aperture 1: 8;

- angle of view 1 °.

Aberration correction of the lens is at the level of the first performance.

In the lens there are relations:

R₂/R₃=1,009; d₂/f′=0,0015;

R ₁ / R ₂ = 2.17;

R ₂ / R ₃ = 1.009; d ₂ / f ′ = 0.0015;

In this lens design, the radii of the second and third surfaces R ₂ and R _{3 are} concentric (i.e., R ₂ = R ₃ + d ₂ ). This allows you to control the correct alignment of the lens with a simple and clear autocollimation method, while simultaneously observing the autocollimation images of the second and third surfaces, and actually carry out the adjustment by combining these images with lens movements.

In both versions, the lens is made with spherical surfaces, which makes it possible to manufacture it industrially.

Claims (2)

1. A two-lens lens, consisting of the negative meniscus convex towards the subject and a biconvex lens located along the rays, characterized in that it has the following relations:
2,0 <R ₁ / R ₂ <3.0,
| R ₁ / R ₄ | <0,08,
0.9 <R ₂ / R ₃ <1.1,
d ₂ / f ′ <0.002,
| ν ₁ -ν ₂ |> 34,
| p ₁ -p ₂ | <0.001,
where R ₁ , R ₂ , R ₃ , R ₄ , are the radii of the first, second, third and fourth surfaces of the lenses of the lens along the rays, respectively; d _{2 is the} air gap between the lenses; f ′ is the focal length of the lens; ν ₁ and ν ₂ are the dispersion coefficients of the glass of the first and second lenses of the lens, respectively; p ₁ and p ₂ are the relative partial dispersions of the glass of the first and second lenses of the lens, respectively. 2. A two-lens lens according to claim 1, characterized in that the radii of the second and third surfaces R ₂ and R ₃ along the rays are concentric.