RU2711626C1 - Fast lens - Google Patents

Abstract

FIELD: optics; data processing.SUBSTANCE: lens can be used in digital sighting devices with megapixel CCD or CMOS matrices in day and night conditions. Lens has two components, the first of which comprises a biconvex lens and a convex-concave lens which faces the object with its concave side, the second one – a biconvex lens, the second surface of which is an aspherical, biconvex and biconcave lens. Biconvex and biconcave lenses of the second component are glued together. Aperture diaphragm is located on the second surface of the negative lens of the first component. Following ratios are met: 1.5<|F/F|<2.5, 1.2<|F/F|<1.9, where Ffocal length of the lens; F– focal distance of second lens of first component; Fis focal distance of second component first lens.EFFECT: increasing the luminosity of lens to 1:1 and providing image quality at spatial frequencies of up to 130 g/mm.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 devices with image formation on megapixel CCD or CMOS sensors in day and night operating conditions.

A known lens for the visible and near infrared spectral range (patent RU 2421764 C1, publ. 06/20/2011) containing five lenses mounted in series on the optical axis, grouped into three components, the first of which contains three optical elements - a positive biconvex lens, a positive meniscus and a negative biconcave lens, the second component is made in the form of an asymmetric biconvex lens, the third component is made in the form of a negative plane-concave lens. The aperture diaphragm is located on the second surface of the third element of the first component, a relative aperture of 1: 1.6 and an angular field in the space of objects of 13 ° are provided, while the image quality of a point on the axis and in the field in the spectral range of orth 486 to 852 nm is good, modulation transmission coefficient at frequencies up to 100 lines / mm is at least 10%.

The disadvantage of this lens for the visible and near-IR spectral regions is the low aperture ratio of 1: 1.6, the relatively narrow spectral working range Δλ = (486 ÷ 852) nm, and the low modulation transmission coefficient, which does not allow it to be used for digital devices based on a CCD or CMOS photodetector with a pixel size of less than 5 microns.

A known lens for the infrared region of the spectrum (patent RU 2175774, publ. 10.11.2001), containing five lenses grouped into two components, the first of which consists of a positive lens and a double-glued meniscus, consisting of a biconvex and biconcave lenses, and the second component contains a negative a meniscus convex to the subject and a positive lens. The first lens in the first component is biconvex, and the second lens in the second component is a positive meniscus with a concavity towards the object. A relative aperture of 1: 1.8 and an angular field in the space of objects of 5 ° are provided in the lens with good image quality in the spectral range from 0.66 to 0.92 μm.

The disadvantage of this lens for the IR region of the spectrum is its low aperture ratio (equal to 1: 1.8) and the relatively narrow spectral working range Δλ = (0.66 ÷ 0.92) μm, as well as the low modulation transmission coefficient, which also does not allow its use for digital devices based on CCD or CMOS photodetectors with a pixel size of less than 5 microns.

The closest in technical essence is a fast lens (patent RU 2181208, publ. 04/10/2002) containing five lenses, the first of which is a biconvex lens, the second is a negative lens made in the form of a concave lens, the third is a biconvex lens, the second surface of which aspherical, the fourth is a biconvex lens, and the fifth is a biconcave lens. The aperture diaphragm is located between the second and third lenses. A relative aperture of 1: 1.6 and an angular field in the space of objects of 38 ° are provided in the lens with good image quality in the spectral range from 0.6 to 1.0 μm, the modulation transmission coefficient at frequencies up to 100 lines / mm is at the level of 10 ÷ fifteen%.

The disadvantage of this aperture lens is a low aperture ratio of 1: 1.6, as well as a relatively low modulation transmission coefficient, at a spatial frequency of more than 100 lines / mm, which does not allow it to be used for digital devices based on megapixel CCD or CMOS photodetectors with a pixel size less than 5 microns.

The objective of the present invention is to increase the aperture ratio of the lens to a value of 1: 1 and to ensure image quality at spatial frequencies up to 130 lines / mm.

The technical result due to the task is achieved by the fact that in a fast lens containing an aperture diaphragm and five lenses grouped into two components, the first of which contains a biconvex lens and a negative lens, the second contains a biconvex lens, the second surface of which is aspherical, biconvex and biconcave lenses, in contrast to the known, the negative lens of the first component is convex, facing concavity to the object, biconvex and biconcave lenses of the second component are gluing, and the aperture diaphragm is located on the second surface of the negative lens of the first component, while the following relationships are true:

1.5 <| F ₂ / F _ABOUT | <2.5,

1,2 <| F ₃ / F _ON | <1.9,

where F _AB is the focal length of the lens;

F ₂ is the focal length of the second lens of the first component;

F ₃ is the focal length of the first lens of the second component.

Such a fast lens provides an increase in the lens aperture to a value of 1: 1 and higher image quality at spatial frequencies up to 130 lines / mm.

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

The fast lens contains two components I and II sequentially located on the optical axis. The first component I contains a positive biconvex lens 1 and a negative lens 2, an aperture diaphragm 3 is located on the second surface of the lens 2 of component I, the second component II contains a positive biconvex lens 4, the second surface of which is aspherical, biconvex lens 5 and a biconcave lens 6 glued together , protective glass of photodetector 7 and photodetector 8.

The design parameters of the high-aperture lens embodiment are shown in table 1.

Parameters of aperture lens design option:

- estimated wavelength 0.7 microns; - working spectral range (0.5 ÷ 0.9) μm; - focal length 18.0 mm; - linear field of view 6.0 mm; - angular field of view ~ 18.9 °; - relative hole 1: 1

The principle of operation of a fast lens is as follows.

The first component I, made of a positive biconvex lens 1 and a convex concave lens 2, facing concavity to the object, is a power element that forms a small optical power and provides partial correction of spherochromatic aberration, coma and secondary spectrum. The second component II, made in the form of a positive biconvex lens 4, the second surface of which is an aspherical, biconvex lens 5 and a biconcave lens 6, glued together, is a power and correction element that allows you to correct the image curvature, astigmatism and aberrations of wide beams. The location of the aperture diaphragm 3 on the second surface of the lens 2 of the first component I avoids the vignetting of inclined beams. In a fast lens, the following relationships must be fulfilled:

1.5 <| F ₂ / F _ABOUT | <2.5,

1.2 <| F ₃ / F _ABOUT | <1.9,

where F _AB is the focal length of the lens;

F ₂ is the focal length of the second lens of the first component;

F ₃ is the focal length of the first lens of the second component.

Asked by the quality criterion - the value of the polychromatic contrast transfer coefficient (CPC) and given

- the thickness of the protective glass 7 of the photodetector 8, equal to 0.75 mm;

- spectral efficiency at wavelengths, taking into account the sensitivity of the photodetector 8 and the light transmission of the lens - 1.0 at a wavelength of 0.5 μm, 0.9 at a wavelength of 0.6 μm, 0.6 at a wavelength of 0.7 μm, 0, 4 at a wavelength of 0.8 μm and 0.2 at a wavelength of 0.9 μm;

- spatial frequency ~ 130 lin / mm (Nyquist frequency for a photodetector 6 format 1280 × 960 pixels with a pixel size equal to 3.75 μm),

we obtain the following calculated values of the qualitative characteristics of the fast lens:

- diffraction quality PDA = 89.3% - for a point on the axis PDA = 43.0% - for a field point of 1.8 mm from the center Images CPC _M = 28.2% CPC _C = 28.4% - for a field point of 2.4 mm from the center Images PDA _M = 32.9% PDA _C = 9.87% - for a field point of 3.0 mm from the center Images PDA _M = 9.17% PDA _C = 6.46%

Calculations show that a fast lens provides good image quality for optoelectronic devices using a television matrix with a megapixel format in the spectral range (0.5 ÷ 0.9) μm with a pixel size of 3.75 μm. A high value of the relative aperture is 1: 1 in contrast to the prototype's 1: 1.6, and high image quality expands the range of possible applications of the fast lens, in particular, allows it to be used more efficiently for day and night vision with high resolution in low light conditions ( at twilight and in the dark).

Claims (6)

A fast lens containing an aperture diaphragm and five lenses grouped into two components, the first of which contains a biconvex lens and a negative lens, the second a biconvex lens, the second surface of which is aspherical, biconvex and biconcave lens, characterized in that the negative lens of the first component is convex facing the object, the biconvex and biconcave lenses of the second component are glued, and the aperture diaphragm is located on the second surface ty of the negative lens of the first component, while the following relationships are true: 1.5 <| F ₂ / F _ABOUT | <2.5, 1.2 <| F ₃ / F _ABOUT | <1.9, where F _AB is the focal length of the lens; F ₂ is the focal length of the second lens of the first component; F ₃ is the focal length of the first lens of the second component.

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