RU2445657C1 - Four-element lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: lens has, on the beam path, a double-lens component glued from a converging-meniscus lens whose convex side faces the object and a divergent-meniscus lens whose concave side faces the image, a single biconcave lens and a single biconvex lens. An aperture diaphragm is located behind the last biconvex lens. Radii of optical surfaces, refraction indices and dispersion coefficients of optical material of the lenses and the focal distance of the lens satisfy the certain relationships given in the claim.

EFFECT: high aperture ratio, larger field angle in the object space and high technological effectiveness.

3 cl, 1 dwg, 2 tbl

Description

The invention relates to optical instrumentation and can be used as a receiving lens in optical devices operating with various photodetectors.

A four-lens lens is known (US Patent No. 2,338,614, publ. 1944), consisting along the rays of four single lenses: the first biconvex, the second biconcave, the third biconcave, and the fourth biconvex. However, this lens has an insufficient relative aperture of 1: 4.5 and insufficient manufacturability, since all the radii of the optical surfaces of this lens are different.

The closest analogue to the claimed technical solution is a three-component four-lens photographic lens (US Patent No. 2854889, publ. 1958), consisting of three components separated by air gaps, the first of which is glued from a biconvex and biconcave lens, the second one a single biconcave lens and the third is a single biconvex lens, and there are relations:

1.63 <n ₃ <(n ₁ + n ₄ ) / 2-0.04

0.8f <R ₁ + R ₅ <0.9f

4,5R ₁ <R ₃ <10R ₁

n ₁ > n ₂

n ₃ <n ₄

ν ₄ = 54.8

where n ₁ , n ₂ , n ₃ , n ₄ are the refractive indices of the material along the rays of the first, second, third and fourth lenses for the spectrum line d;

R ₁ , R ₂ , R ₃ - the radii of curvature of the first, third and fifth optical surfaces along the rays;

ν ₄ is the dispersion coefficient of the material of the fourth lens for the spectrum line d;

f is the focal length of the entire lens.

However, this lens has an insufficient relative aperture of 1: 2.8; insufficient angular field in the space of objects 2W = 45 degrees. and lack of manufacturability, since all the radii of the optical surfaces of this lens are different.

The objective of the invention is to provide a lens with enhanced performance.

The technical result is an increase in the relative aperture, angular field in the space of objects and an increase in manufacturability.

This is achieved by the fact that in a four-lens lens consisting of three components separated by air gaps, the first of which is glued from the positive and negative lenses along the rays, the second is a single biconcave lens and the third is a single biconvex lens, in contrast to the known lens of the first the components are made in the form of menisci, the first of which is convex to the object, and the second is concavity to the image, the lenses of the second and third components are made of the same brand of glass and have elations:

(n ₁ + n ₄ ) / 2-0.04 <n ₃ <1.9

2R ₁ <R ₃ <4R ₁

n ₁ <n ₂

| R ₆ | = | R ₇ |

where n ₁ , n ₂ , n ₃ , n ₄ are the refractive indices of the material along the rays of the first, second, third and fourth lenses for the spectrum line d;

R ₁ , R ₃ , R ₆ , R ₇ are the radii of curvature of the first, third, sixth and seventh optical surfaces along the rays.

In this case, the ratio

0.5f '<R ₁ + R ₅ <0.8f';

where R ₁ , R ₅ are the radii of curvature of the first and fifth optical surfaces along the rays;

f 'is the focal length of the entire lens.

In addition, there may be a ratio:

10 <ν ₄ <40

where ν ₄ is the dispersion coefficient of the fourth lens material for the spectrum line d.

The figure shows an optical diagram of a four-lens.

The four-lens lens consists of three components along the rays, the first of which is glued from the positive meniscus 1, convex to the object and the negative meniscus 2, facing the concavity to the image; the second is a single biconcave lens 3 and the third is a single biconvex lens 4. The aperture diaphragm is located at a distance of 0.9 mm behind the lens 4.

Four-lens works as follows.

The luminous flux emanating from the plane of objects at infinity passes through a four-lens lens and is displayed in the plane of the best setting in which the photodetector (not shown) is located.

As a specific example of implementation of the invention, a four-lens lens is calculated, corrected in the spectral range from 435 nm to 656 nm with the structural data presented in table 1.

The calculated four-lens lens has the following characteristics:

The focal length of the lens f ' 32.05 mm Relative hole 1: 2.7 Angular field in the space of objects 65 deg. Linear field in image space 2U '= 43.26 mm Back focal length 23.42 mm

For this lens, there are relations:

(n ₁ + n ₄ ) / 2-0.04 = 1.701277 <n ₃ = 1.740024 <1.9

2R ₁ = 20.942 <R ₃ = 24.43 <4R ₁ = 41.884

n ₁ = 1.74253 <n ₂ = 1.806274

0.5f '<R ₁ + R ₅ = 0.65192 f'<0.8f'

10 <ν ₄ = 28.16 <40.

Table 1 Radii, mm Thickness mm Glass mark Refractive index n _e Coeff. variance, v _e Light diameter mm R ₁ = 10,471 12.71 d ₁ = 4.58 CTK9 1.746046 fifty R ₂ = 95.28 10.28 d ₂ = l TF10 1,813767 25.17 R ₃ = 24.43 9.56 d ₃ = 0.81 one R ₄ = -34.75 9.56 d ₄ = 0.8 TF4 1,746231 27.95 R ₅ = 10,423 9.1 d ₅ = 0.7 one R ₆ = 20.8 9.1 d ₆ = 2,3 TF4 1,746231 27.95 R ₇ = -20.8 9.2 one

table 2 Type of aberration The proposed four-lens lens (no more) Transverse spherical aberration for a point on the axis with a relative aperture of 1: 2.7 0.05 mm The transverse aberration of a wide inclined beam in the meridional section for an angular field of 2W = 65 deg. -2.717 mm Transverse aberration of a wide inclined beam in a sagittal section for an angular field of 2W = 65 deg. 0.459 mm The meridional astigmatic segment X _m for the angular field 2W = 65 deg. 2.056 mm Sagittal astigmatic segment X _s for the angular field 2W = 65 degrees. 0.092 mm Distortion for the angular field 2W = 65 degrees. 6.11%

Table 2 shows the aberrations for λ = 0.54607 μm for the proposed four-lens objective according to a specific embodiment.

The proposed lens has the same modulus radii of the spherical optical surfaces of the third component, which characterizes its high manufacturability. Thus, as a result of the proposed solution, a technical result is obtained: a four-lens lens with increased relative aperture, angular field in the space of objects and manufacturability is created.

Claims (3)

1. A four-lens lens consisting of three components separated by air gaps, the first of which is glued from the positive and negative lenses along the rays, the second is a single biconcave lens and the third is a single biconvex lens, characterized in that the lenses of the first component are made in the form menisci, the first of which is convex to the object, and the second is concavity to the image, the lenses of the second and third components are made of the same glass brand and there are relations:
(n ₁ + n ₄ ) / 2-0.04 <n ₃ <1.9;
2R ₁ <R ₃ <4R ₁ ;
n ₁ <n ₂ ;
| R ₁ | = | R ₇ |;
where n ₁ , n ₂ , n ₃ , n ₄ are the refractive indices of the material along the rays of the first, second, third and fourth lenses for the spectrum line d;
R ₁ , R ₃ , R ₆ , R ₇ are the radii of curvature of the first, third, sixth and seventh optical surfaces along the rays. 2. The four-lens lens according to claim 1, characterized in that the ratio is:
0.5f '<R ₁ + R ₅ <0.8f';
where R ₁ , R ₅ are the radii of curvature of the first and fifth optical surfaces along the rays;
f 'is the focal length of the entire lens. 3. The four-lens lens according to claim 1, characterized in that the ratio is:
10 <ν ₄ <40;
where ν ₄ is the dispersion coefficient of the fourth lens material for the spectrum line d.