RU2593413C2 - High-aperture lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: lens comprises three lenses. The first lens is a positive meniscus lens whose concave side faces the image. The second lens is negative, and the curvature radius of its first surface r₃ satisfies the relationship

. The third lens is a positive meniscus whose concave side faces the image, for which the relationship

is satisfied, where: f' is the focal distance of the lens, n is the refraction index of the material of the third lens, r₅ is the curvature radius of the first surface of the third lens, r₆ is the curvature radius of the second surface of the third lens, d₅ is thickness on the axis of the third lens. The distance between the first and second lenses is greater than 0.15f'.

EFFECT: high image quality for the middle and far infrared ranges.

7 cl, 1 dwg, 16 tbl

Description

The proposed technical solution relates to optical instrumentation, namely to lens fast lenses for the middle and far infrared (IR) spectral regions, and can be used in thermal imaging devices.

Known fast lenses for the infrared region of the spectrum, containing three lenses, the first of which is a positive meniscus facing concavity to the image, the second lens is negative, the third is positive meniscus facing concavity to the image (US patents No. 4427259, No. 5251063 and Japanese patent No. 62109014).

The lenses presented in US patent No. 4427259 and No. 5251063, have a low enough aperture. In the most aperture lens variants from patent No. 5251063, the aperture does not exceed 1: 1.2 with an angular field of view of 10 °.

The lens presented in Japanese Patent No. 62109014 has a high aperture ratio. However, the thickness of the second lens from Germany is equal to 0.5 of the focal length of the lens, which makes this optical scheme suitable only for short-focus lenses, because as the focal length increases, the overall dimensions, weight and cost of this lens become unacceptably large, and the lens transmission is low.

The closest in technical essence is the lens for the infrared region of the spectrum described in US patent No. 4427259. The lens contains three lenses. The first lens is a positive meniscus with a concavity facing the image. The second is a negative lens. The third lens is a positive meniscus with a concavity towards the image. The lens has a relative aperture of 1: 1.39, an angular field of view of 6.34 ° and works in the spectral region of 3.3-4.2 microns.

The disadvantage of the lens is not high enough aperture and field of view.

The objective of the proposed technical solution is to create a fast three-lens lens with high image quality for the middle and far infrared spectral range.

This goal is achieved by creating a fast lens containing three lenses, the first of which is the positive meniscus facing the concavity to the image, the second lens is negative, the third lens is the positive meniscus facing the concavity of the image, in which, unlike the known for the third lens, the relation

where: f is the focal length of the lens,

n is the refractive index of the material of the third lens,

r ₅ is the radius of curvature of the first surface of the third lens,

r ₆ is the radius of curvature of the second surface of the third lens,

d ₅ is the thickness along the axis of the third lens,

, причем расстояние между первой и второй линзами больше 0,15f.and the radius of curvature of the first surface of the second negative lens r ₃ satisfies the relation

and the distance between the first and second lenses is more than 0.15f.

Besides,

- three lenses are made of optical material of the same brand with a refractive index greater than 3.3,

- the first and third lenses are made of optical material of the same brand with a refractive index greater than 3.3,

- at least one of the surfaces is aspherical,

- on one of the surfaces applied kinoform element,

- one of the surfaces is aspherical and a kinoform element is applied on one of the surfaces,

- the third lens has the ability to move along the optical axis.

In FIG. 1 presents an optical diagram of the proposed aperture lens.

,A fast lens consists of three lenses 1, 2, 3. The first lens 1 is a positive meniscus, facing a concavity to the image. The second lens 2 is negative, in which the radius of curvature of the first surface r ₃ satisfies the relation

,

where: f is the focal length of the lens.

The third lens 3 is a positive meniscus, facing concavity to the image, for which the ratio

where: f is the focal length of the lens,

n is the refractive index of the material of the third lens,

r ₅ is the radius of curvature of the first surface of the third lens,

r ₆ is the radius of curvature of the second surface of the third lens,

d ₅ is the thickness along the axis of the third lens.

The distance between the first and second lenses is more than 0.15f.

The entrance pupil of the lens is the aperture diaphragm located on the first surface of the lens 1.

The lens works as follows. The radiant flux from the object through the entrance pupil enters the lens, passes through lens 1, lens 2, lens 3 in series, and builds an image of the object in the image plane.

The design parameters of some lens options obtained in accordance with the proposed solution are shown in tables 1-9.

The optical characteristics of the lens for the options presented in the table. 1-7:

- focal length - 100 mm;

- relative aperture - 1: 1;

- angular field of view - 13 °;

- spectral range - 8-14 microns.

The optical characteristics of the lens for the options presented in the table. 8, 9:

- focal length - 100 mm;

- relative aperture - 1: 1;

- angular field of view - 13 °;

- spectral range - 3-5 microns.

Thus, the technical result of the proposed solution is the creation of a high-aperture lens for the middle and far infrared spectral regions with a relative aperture of 1: 1, an angular field of view of 13 ° and high image quality.

Claims (7)

1. Fast lens containing three lenses, the first of which is a positive meniscus facing concavity to the image, the second lens is negative, the third lens is a positive meniscus facing concavity to the image, characterized in that for the third lens made in the form of a positive meniscus facing concavity to the image, the relation

where: f ′ is the focal length of the lens,
n is the refractive index of the material of the third lens,
r ₅ is the radius of curvature of the first surface of the third lens,
r ₆ is the radius of curvature of the second surface of the third lens,
d ₅ is the thickness along the axis of the third lens,
and the radius of curvature of the first surface of the second negative lens r ₃ satisfies the relation

moreover, the distance between the first and second lenses is more than 0.15f ′. 2. A fast lens according to claim 1, characterized in that all three lenses are made of optical material of the same brand with a refractive index greater than 3.3. 3. A fast lens according to claim 1, characterized in that the first and third lenses are made of optical material of the same brand with a refractive index greater than 3.3. 4. A fast lens according to claim 1, characterized in that at least one of the surfaces is aspherical. 5. A fast lens according to claim 1, characterized in that a kinoform element is applied on one of the surfaces. 6. A fast lens according to claim 1, characterized in that one of the surfaces is aspherical and a kinoform element is deposited on one of the surfaces. 7. A fast lens according to claim 1, characterized in that the third lens has the ability to move along the optical axis.