RU2762218C1 - Wide-angle retrofocus objective - Google Patents

Abstract

FIELD: photography.SUBSTANCE: objective can be used in reflex photographic equipment. The objective comprises two components. The first component is positive and comprises consecutively arranged positive meniscus lens facing the space of the object with the convex surface, a first, second and third negative meniscus lenses facing the space of the object with the convex surface, a single biconvex lens, a fourth negative meniscus lens facing the space of the object with the convex surface, and a positive double-adhered meniscus lens facing the space of the object with the convex surface and consisting of a biconvex and a biconcave lenses. The second component is positive and comprises a first positive adhered doublet consisting of a negative meniscus lens facing the space of the object with the convex surface and a biconvex lens, and a second negative adhered doublet consisting of a negative meniscus lens facing the space of the object with the convex surface and a biconvex lens.EFFECT: improved image quality over the field and increased manufacturability due to the reduction in the amount of used grades of glass with the maintained relative aperture and the value of the angular field of view.2 cl, 2 dwg, 1 tbl

Description

The invention relates to optical instrumentation and can be used as a photographic lens in SLR cameras.

Known wide-angle retrofocus lenses designed to work with full-frame SLR cameras, patents JP20044226740, Japan, publ. 08/12/2004: relative aperture 1 / 2.89, focal length ƒ '= 16.1 mm; US20110317282, USA, publ. 12/29/2011: relative aperture 1 / 1.84, focal length ƒ '= 18.4 mm; WO2017157812, publ. 09/21/2017: relative aperture 1/4, focal length ƒ '= 11.5 mm. They have a complex optical design, which includes from 14 to 16 lenses from at least 9 different optical materials. In this case, the lenses contain from 2 to 5 aspherical surfaces of the highest order. In addition, the distance from the first surface of the lenses to the image plane exceeds 140 mm. All of the above not only negatively affects manufacturability, but also reduces the consumer properties of these lenses.

Known wide-angle retrofocus lens for patent US5917663 - version No. 3, USA, publ. 29.06.1999. The lens contains two components, separated by an aperture diaphragm. The first component includes the first positive meniscus facing the convexity of the object space, the first and second negative menisci facing the convexity of the object space, a triple-glued negative lens including a biconvex, biconcave and convex-flat lenses, a single biconvex lens and a second positive concavity facing object space.

The second component includes a negative glued doublet consisting of a positive meniscus concavity facing the object space and a biconcave lens, a positive meniscus concavity facing the object space, and a single biconvex lens. The lens is designed to work with a SLR camera, has a 1 / 2.8 aperture, focal length ƒ '= 20.4 mm and a linear image field 2y' = 43 mm. But this lens has a low image quality in the field of view, as well as low manufacturability due to the use of a triple glued lens unit and eight different brands of glasses in the optical scheme.

The closest technical solution to the proposed invention is a wide-angle retrofocus lens according to patent US4061421 - version No. 1, USA, publ. 6.12.1977. The lens contains two components separated by an aperture diaphragm. The first component includes a positive meniscus facing the convexity of the object space, the first and second negative meniscus facing the convexity of the object space, a single biconvex lens, the third negative meniscus facing the convexity of the object space, and a positive glued doublet consisting of a negative meniscus facing the convexity to the object space, and a biconvex lens. The second component includes a negative glued doublet, consisting of a positive meniscus, concavely facing the object space, and a biconcave lens, the first and second positive menisci, concavely facing the object space. The lens has a 1 / 3.5 aperture ratio, a focal length ƒ '= 18.5 mm (in terms of working with a full-frame SLR camera) and an angular field of view 2ω = 100 °. But this lens has a low image quality in the field of view, as well as low manufacturability due to the use of nine different brands of glasses in the optical system.

The problem to be solved by the present invention is to improve the quality of the image in the field of view and increase the manufacturability by reducing the number of used brands of glasses while maintaining the relative aperture and the magnitude of the angular field of view.

EFFECT: improved image quality in the field and improved manufacturability by reducing the number of used glass grades while maintaining the relative aperture and the magnitude of the angular field of view.

This is achieved by the fact that in a wide-angle retrofocus lens, consisting of two components installed along the beam path, the first of which is positive and contains a positive meniscus facing the convexity of the object space, the first and second negative meniscus facing the object space with a convexity, a single biconvex lens, the third negative meniscus, convex facing the object space, and a positive double-glued lens, the second component is positive, in contrast to the known one, in the diagram of the first component between the second negative meniscus, convex facing the object space, and a single biconvex lens, a negative meniscus facing the convexity is included space of the object, and the positive double-glued lens is made in the form of a positive double-glued meniscus, convex facing the object space and consisting of biconvex and biconcave lenses, while the gluing orientation is reversed, the scheme of the second component The enta contains the first positive glued doublet consisting of a negative meniscus facing the object space and a biconvex lens, and a second negative glued doublet consisting of a negative meniscus facing the object space and a biconvex lens.

In addition, a wide-angle retrofocus lens can meet the following conditions:

1.65 <n ₁ = n ₂ = n ₄ = n ₆ = n ₈ <1.66,

57 <ν ₁ = ν ₂ = ν ₄ = ν ₆ = ν ₈ <58,

1.75 <n ₃ = n ₇ = n ₉ = n ₁₁ <1.76,

27 <ν ₃ = ν ₇ = ν ₉ = ν ₁₁ <28,

1.48 <n ₅ = n ₁₀ = n ₁₂ <1.49,

70 <ν ₅ = ν ₁₀ = ν ₁₂ <71,

where: n _i is the refractive index of the i-th lens of a wide-angle retrofocus lens,

ν _i is the dispersion value of the i-th lens of a wide-angle retrofocus lens.

The invention is illustrated by drawings:

- Fig. 1. Circuit diagram of a wide-angle retrofocus lens

- Fig. 2. Polychromatic frequency-contrast characteristic of a wide-angle retrofocus lens at a relative aperture of 1 / 3.5

To solve the problem, a wide-angle retrofocus lens (Fig. 1) is proposed, consisting of two components separated by an aperture diaphragm, the first of which is positive and contains a positive meniscus 1 located in series, facing the object space with a convexity, the first, second and third negative menisci 2, 3 and 4, respectively, facing the convexity of the object space, a single biconvex lens 5, the fourth negative meniscus 6, convex facing the object space, and a positive double-glued meniscus, convex facing the object space, and consisting of biconvex and biconcave lenses 7 and 8, accordingly, the second component is positive and contains a first positive glued doublet consisting of a negative meniscus 9, convex to the object space, and a biconvex lens 10, and a second negative glued doublet, consisting of a negative meniscus 11, convex to a simple object, and a biconvex lens 12.

As an example of a specific implementation, a wide-angle retrofocus lens is proposed, designed to work with a SLR camera, with a focal length ƒ '= 18 mm, a relative aperture of 1 / 3.5 and an angular field of view of 2ω = 100 °.

The essence of the invention is that the improvement of the image quality in the field of view is achieved by including the first component in the circuit, additionally, one more negative meniscus and replacing two single lenses in the second component with a glued doublet, which made it possible to redistribute the correction load between negative menisci and a single positive lens, thereby significantly reducing spherical aberration and astigmatism. At the same time, in the second component, additional gluing made it possible to correct the transverse chromatism and, along with a single positive lens of the first component, to compensate for the distortion introduced by negative menisci. This design of the lens scheme made it possible to improve the contrast in the image at a spatial frequency of 30 mm ^{-1 by} almost a third for the axial point of the field and at least 2 times in the field of view. In addition, the number of used glass grades was reduced from nine to three.

The lens works as follows: light beams emanating from an object located at infinity, successively pass the Ι-components of the optical system and form an image in the plane of the best installation.

Table 1 shows the design parameters of an example of a specific design.

A wide-angle retrofocus lens with a relative aperture of 1 / 3.5 provides a resolution of 30 mm ^-1 for the center of the field with a contrast of more than 78%, along the field from y '= 0 mm to y' = 19 mm with a contrast of more than 38%. The distortion module over the entire image field does not exceed 2.5%.

Thus, in the claimed wide-angle retrofocus lens, the previously presented technical result has been achieved - the image quality in the field is improved and manufacturability is increased by reducing the number of used glass brands while maintaining the relative aperture and angular field of view.

Claims (5)

1. A wide-angle retrofocus lens consisting of two components installed along the beam path, the first of which is positive and contains a positive meniscus facing the convexity of the object space, the first and second negative menisci facing the convexity of the object space, a single biconvex lens, the third negative meniscus, convex to the object space, and a positive double-glued lens, the second component is positive, characterized in that the scheme of the first component between the second negative meniscus, convex to the object space, and a single biconvex lens includes a negative meniscus, convex to the object space, and the positive the double-glued lens is made in the form of a positive double-glued meniscus, convex facing the object space and consisting of biconvex and biconcave lenses, while the gluing orientation is reversed, the scheme of the second component contains the first A single glued doublet consisting of a negative meniscus facing the object space and a biconvex lens, and a second negative glued doublet consisting of a negative meniscus facing the object space and a biconvex lens. 2. Wide-angle retrofocus lens according to claim 1, characterized in that the lens meets the following conditions:

where: n _i is the refractive index of the i-th lens of a wide-angle retrofocus lens, ν _i is the dispersion value of the i-th lens of a wide-angle retrofocus lens.

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