RU2662022C1 - High-aperture lens - Google Patents

Abstract

FIELD: instrument engineering.

SUBSTANCE: lens can be used in digital sighting and observation devices with the images formation on the CCD or CMOS matrices under day and night conditions. First component comprises biconvex lens and negative concave-convex lens facing the image with convexity, second one is the single positive meniscus lens, facing the images space with concavity, third one is the negative meniscus lens and the positive meniscus lens, facing the image with concavity, fourth one is the negative meniscus lens, facing the image with concavity. Aperture diaphragm is located in front of the first component. Following ratios are met: d_1-2=(0.8÷2.0)⋅F_LENS, n_3-1=n₄≥2.0; where F_LENS is the lens focal distance; d_1-2 is the air gap between the first and second components; n_3-1 is the third component first lens refraction index; n₄ is the fourth component lens refraction index. As a result, enabling increase in the optical efficiency to the value of 1:0.85 with the spectral operating range extension to Δλ=(600…1,000) nm and the image quality improvement at spatial frequencies 90…100 lines/mm with polychromatic modulation transmission coefficients at the level of at least 0.4 in the field of view center and at least 0.3 at the field of view edge.

EFFECT: increase in the optical efficiency with the spectral operating range expansion and improvement in the image quality.

1 cl, 1 dwg, 1 tbl

Description

The present invention relates to the field of optoelectronic technology and can be used as a lens in digital sighting and observational devices with image formation on CCD or CMOS sensors in day and night operating conditions.

Known fast lens (patent RU 2386988 C1, publ. 04/20/2010) containing six lenses formed in four components with an aperture diaphragm located in front of the first component, and the first component is made in the form of a double-glued lens, consisting of a biconvex and biconcave lenses, the second the component is made in the form of a double-glued meniscus, consisting of a biconcave and biconvex lens. The lens operates in the spectral range Δλ = (600 ... 900) nm and has a relative aperture of 1: 2 and a field of view of 4 °.

The disadvantage of this aperture lens is a low aperture ratio of 1: 2, a small field of view of 4 °, a relatively narrow spectral working range Δλ = (600 ... 900) nm, and the presence of two bonded lenses in it, which complicates the technology of its manufacture.

The closest in technical essence is a fast lens (patent RU 2411556 C1, publ. 02/10/2011) containing six lenses formed into four components with an aperture diaphragm located on the surface of the second component facing the image space, and the first component is made in the form single positive lens, the second component is made in the form of gluing from a positive asymmetric biconvex lens facing the first component with a surface with a smaller radius of curvature, and a negative asymmetric a biconcave lens facing a surface with a smaller radius of curvature to the image space, the third component is made in the form of gluing from the negative meniscus and a biconvex lens facing the image space with a surface with a large radius of curvature, and the fourth in the form of an asymmetric biconcave lens facing the image space surface with a large radius of curvature. The lens operates in the spectral range Δλ = (486.1 ... 656.3) nm and has a relative aperture of 1: 1 and an angular field of view of 10 °.

The disadvantage of this aperture lens is a low aperture ratio of 1: 1, a relatively narrow spectral working range Δλ = (486.1 ... 656.3) nm, low image quality at spatial frequencies of 90 ... 100 lines / mm with polychromatic modulation transmission coefficients at a level ~ 0.2, as well as the presence of two glued lenses in it, which complicates the technology of its manufacture.

The objective of the present invention is to increase the lens aperture to a value of 1: 0.85 with the expansion of the spectral operating range to Δλ = (600 ... 1000) nm and to improve image quality at spatial frequencies of 90 ... 100 lines / mm with polychromatic modulation transmission coefficients at a level not less than 0.4 in the center of the field of view and not less than 0.3 at the edge of the field of view.

The technical result due to the task is achieved by the fact that in a fast lens containing four components sequentially located on the optical axis, the first of which contains a positive lens, the second component contains a positive lens, the third component contains a negative meniscus, and the fourth contains a negative lens, unlike the known one, the first component contains two lenses, the first of which is made in the form of a positive biconvex lens, and the second lens is made in the form of a negative of the concave-convex lens convex to the image space, the second component contains a single positive meniscus facing the concavity to the image space, the third component contains two lenses, the second of which is made in the form of a positive meniscus facing the concavity to the image space, the fourth component is made in in the form of a negative meniscus facing concavity to the image space, and the aperture diaphragm is located in front of the first surface of the first component, while the following relations:

d _1-2 = (0.8 ÷ 2.0) ОБF _OB ,

n _Z-1 = n ₄ ≥2.0;

where F _AB is the focal length of the lens;

d _1-2 is the air gap between the first and second components;

n _3-1 is the refractive index of the first lens of the third component;

n ₄ - refractive index of the fourth lens component.

Such a fast aperture lens provides a higher aperture ratio of the lens to a value of 1: 0.85 and an expanded spectral working range to Δλ = (600 ... 1000) nm with improved optical characteristics.

The optical scheme of the fast lens is shown in figure 1.

A fast lens contains four components sequentially located on the optical axis. Aperture diaphragm 1 is located in front of the first component, the first component is made in the form of a positive lens 2 and a negative lens 3, the second component is made in the form of a single positive lens 4, the third component is made in the form of a negative lens 5 and positive lens 6, the fourth component is made in the form of a negative meniscus 7, after which there is a protective glass 8 and a photodetector 9.

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

The parameters of this embodiment of the fast lens:

estimated wavelength 0.8 μm working spectral range (0.6 ÷ 1.0) μm focal length 25.0 mm linear field of view 4,5 mm angular field of view ~ 10.2 ° relative hole 1: 0.85

The principle of operation of the optical system is as follows.

The first component I, made in the form of a positive lens 2 and a negative concave-convex lens 3, convex to the image space, in combination with the second component II, made in the form of a single positive meniscus 4, are power elements that form an optical power close to optical the strength of the lens, for which it is necessary to perform the following ratio:

d _1-2 = (0.8 ÷ 2.0) ОБF _OB ,

where F _AB is the focal length of the lens;

d _1-2 is the air gap between the first and second components.

The third component III, made in the form of two lenses - a negative meniscus 5 and a positive meniscus 6, facing concavity to the image space, in combination with the fourth component IV, made in the form of a negative meniscus 7, facing concavity to the image space, are correction elements that allow to provide a high degree of correction of spherochromatic aberration, coma and secondary spectrum, as well as correct image curvature, astigmatism and aberration of wide inclined beams, for which it is necessary imo fulfill the following relationship:

n _W-1 = n ₄ ≥2.0,

where n _3-1 - refractive index of the first lens of the third component;

n ₄ - refractive index of the fourth lens component.

Setting the quality criterion - the value of the polychromatic contrast transfer coefficient (CPC) and taking into account:

- the thickness of the protective glass 8 of the photodetector, equal to 0.75 mm;

- spectral efficiency at wavelengths taking into account the sensitivity of the photodetector and the light transmission of the lens - 0.8 at a wavelength of 0.6 μm, 0.9 at a wavelength of 0.7 μm, 1.0 at a wavelength of 0.8 μm, 0.8 at a wavelength of 0.9 μm and 0.4 at a wavelength of 1.0 μm;

- spatial frequency ~ 90 lin / mm (Nyquist frequency for a photodetector with a sensor element size equal to 5.625 μm), we obtain the following calculated values of the qualitative characteristics of a fast lens:

diffraction quality PDA = 92.3% for a point on the axis PDA = 45.1% for a field point 1.5 mm from the center CPC _M = 46.0% Images CPC _C = 43.4% for a field point of 2.2 mm from the center CPC _M = 31.4% Images PDA _C = 42.5%

As can be seen from the calculations, the optical system, with the simplicity of its design, provides good image quality for optoelectronic devices using a television matrix of the spectral range (0.6 ÷ 1.0) microns with a pixel size of 5.625 microns. The high value of the relative aperture is 1: 0.85 (the prototype has 1: 1) significantly expands the range of possible use of the lens, in particular, it can be used for night vision in low light conditions (twilight and dark).

Claims (7)

A fast lens containing four components in series on the optical axis, the first of which contains a positive lens, the second component contains a positive lens, the third component contains a negative meniscus, and the fourth a negative lens, characterized in that the first component contains two lenses, the first of which made in the form of a positive biconvex lens, and the second lens is made in the form of a negative concave-convex lens, convex to the image space, the second to the component contains a single positive meniscus facing concavity to the image space, the third component contains two lenses, the second of which is made in the form of a positive meniscus facing concavity to the image space, the fourth component is made in the form of a negative meniscus facing concavity to the image space, and the aperture diaphragm located in front of the first surface of the first component, the following relationships are true: d _1-2 = (0.8 ÷ 2.0) ОБF _OB , n _3-1 = n ₄ ≥2.0; where F _AB is the focal length of the lens; d _1-2 is the air gap between the first and second components; n _3-1 is the refractive index of the first lens of the third component; n ₄ - refractive index of the fourth lens component.

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