RU2281537C1 - Three-element telephoto lens - Google Patents

Abstract

FIELD: optical instrument engineering, applicable in various optical systems.

SUBSTANCE: the three-element telephoto lens has two components, the first of which is a positive one and consists of two similar menisci turned by the convexity to the object, the second component is a biconcave lens with radii similar in modulus. The relations between the value of the second air gap, focal length of the objective lens and the indices of refraction and the dispersion factors for the line from the second and third lenses are realized in the telephoto lens.

EFFECT: enhanced focal length, reduced length and enhanced adaptability to manufacture at a high quality of image for the point of the axis.

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Description

The present invention relates to optical instrumentation and can be used in various optical, including infrared systems.

Known photographic telephoto lens (Swiss Patent No. 339394, NKI 42N, 4/10, publ. 1959), containing two components, the first of which (along the rays) is positive, consisting of two single lenses - biconvex and biconcave; and the second component is a glued negative meniscus, convex to the image and consisting (along the rays) of the negative and positive menisci.

However, this telephoto lens has a large length, complex design and lack of manufacturability (consists of four different lenses).

The closest analogue to the claimed technical solution is a telephoto lens (M.I. Apenko, L.A. Zapryagaeva, I.S.Sveshnikova "The Problem in Applied Optics", Moscow: Nedra, 1987, p. 303), containing two components, the first of which (along the rays) - positive, consisting of two single lenses - biconvex and negative meniscus, convex to the image; and the second component is a single biconcave lens with equal radii in absolute value. This lens is corrected in the spectral range from 480 to 644 nm.

Lens Specifications:

focal length f ' 320.07 mm optical system length (distance from first to last optical surfaces) 191 mm back focal length 43.43 mm telephoto coefficient K _T 0.7324

The conditions are met:

d ₂ / f '= 0.002

n ₂ = 1.6169

n ₃ = 1.5183

ν ₂ = 36.7

ν ₃ = 63.83,

where: d ₂ - the size of the second air gap;

f'- focal length of the entire lens;

n ₂ , ν ₂ - refractive index and dispersion coefficient for line e of the material of the second lens;

n ₃ , ν ₃ - refractive index and dispersion coefficient for line e of the material of the third lens.

This telephoto lens has a small focal length, a large length and lack of manufacturability (since all the lenses in the lens are different).

The objective of the invention is the creation of a three-lens telephoto lens with an increased focal length, reduced length and high adaptability with high image quality for a point on the axis.

The technical result due to the task is achieved by the fact that in a three-lens telephoto lens containing two components, the first of which (along the rays) is positive, consisting of two separate lenses, the second is a single biconcave lens with equal radii in absolute value; unlike the known, the first component consists of two identical, positive menisci, convex to the object, and the conditions are satisfied:

0.03 <d ₂ / f '<0.1

1.4 <n ₂ <1.616

1.75 <n ₃ <1.9

50 <ν ₂ <72

20 <ν ₃ <27.7,

where: d ₂ - the size of the second air gap;

f 'is the focal length of the entire lens;

n ₂ , ν ₂ - refractive index and dispersion coefficient for line e of the material of the second lens;

n ₃ , ν ₃ - refractive index and dispersion coefficient for line e of the material of the third lens.

The drawing shows an optical diagram of the proposed lens.

A three-lens telephoto lens consists of two components sequentially located along the rays from the object, the first of which consists of two single identical, positive menisci 1 and 2, convex to the object, and the second is a biconcave lens 3.

The proposed lens works as follows: the light flux from an object located at infinity enters the lens, where it passes through lenses 1-3 and forms an image of the object in the plane of the best setup in which the optical radiation receiver (not shown) is installed.

The proposed optical system can also work as a collimator lens in the reverse ray path.

In accordance with the proposed solution, a telephoto lens was calculated, corrected in the spectral range from 863 to 951 nm, with the main calculated wavelength λ = 900 nm.

The design parameters of the telephoto lens are shown in table 1.

Characteristics of the calculated lens:

focal length f ' 428.85 mm relative hole 1: 42.9 field of view angle 1 degree 40 ' optical system length (distance from first to last optical surfaces) 29.26 mm distance from last optical surface to the plane of best fit 55.52 mm telephoto coefficient K _T 0.1977

The conditions are met:

d ₂ / f '= 0.05494

n ₂ = 1,615192

n ₃ = 1.813767

ν ₂ = 58.09

ν ₃ = 25.17,

where: d ₂ - the size of the second air gap;

f 'is the focal length of the entire lens;

n ₂ , ν ₂ - refractive index and dispersion coefficient for line e of the material of the second lens;

n ₃ , ν ₃ - refractive index and dispersion coefficient for line e of the material of the third lens.

The entrance pupil in the three-lens telephoto lens is placed at a distance of 4.5 mm in front of the first optical surface, but can also be located in another place.

Table 1. Telephoto lens design Radii, mm Thickness mm Glass mark Refractive index n _e Coeff. variances ν _e Light diameter mm R ₁ = 29.509 10,2 d ₁ = 2,3 Tk16 1,615192 58.09 R ₂ = 112,468 10,2 d ₂ = 0.2 one R ₃ = 29.509 10,2 d ₃ = 2,3 Tk16 1,615192 58.09 R ₄ = 112,468 10,2 d ₄ = 23.56 one R ₅ = -9.817 3 d ₅ = 0.9 TF10 1,813767 25.17 R ₆ = 9.817 3

Table 2 shows the aberrations for λ = 900 nm of the calculated version of the telephoto lens.

table 2 Type of aberration The proposed fast lens (no more) Transverse spherical aberration for a point on the axis with a relative aperture of 1: 42.9 0.02 mm Transverse aberration of a wide inclined beam in the meridional section for the field of view 2W = 1 deg. 40 min 0.16 mm Transverse aberration of a wide inclined beam in the sagittal section for the field of view 2W = 1 deg. 40 min 0.033 mm The meridional astigmatic segment X _m for the field of view 2W = 1 deg. 40 min 7.44 mm Sagittal astigmatic segment X _s for the field of view 2W = 1 deg. 40 min 6.45 mm Distortion for the field of view 2W = 1 deg. 40 min 0.69%

Thus, as a result of the proposed solution, the technical result was obtained: a three-lens telephoto lens was created with a focal length increased to 428.85 mm, with a reduced length and increased manufacturability with high image quality for a point on the axis.

Claims (1)

A three-lens telephoto lens containing two components, the first of which (along the rays) is positive, consisting of two separate lenses, the second is a single biconcave lens with radii equal in absolute value, characterized in that the first component consists of two identical positive menisci, convex to the subject, and the conditions are met 0.03 <d ₂ / f '<0.1; 1.4 <n ₂ <1.616; 1.75 <n ₃ <1.9; 50 <ν ₂ <72; 20 <ν ₃ <27.7, where d ₂ is the magnitude of the second air gap; f 'is the focal length of the entire lens; n ₂ , ν ₂ - refractive index and dispersion coefficient for line e of the material of the second lens; n ₃ , ν ₃ - refractive index and dispersion coefficient for line e of the material of the third lens.