RU2451312C1 - Objective lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: objective lens has two components and an aperture diaphragm in between. The first component comprises a biconvex and a diverging lens and is augmented with a converging meniscus whose concave surface faces the image space and the diverging lens lying after it. The second component is a diverging meniscus whose concave surface faces the image space, made from a biconvex lens and a biconcave lens glued together and having thickness on the optical axis which is not less than 0.07 times the focal distance of the objective lens. The converging lens of the first component is made from glass with refraction index of not more than 1.5 and Abbe number of not less than 80. The distance between the components is not less than 0.13 times the focal distance of the objective lens.

EFFECT: high image quality owing to higher modulation transfer constants on the entire field of vision and keeping the length of the objective lens short.

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Description

The invention relates to optical instrumentation, namely to lenses, and can be used as a camera lens with image formation on a CCD matrix.

A lens [1] of three components is known, the first of which is a positive meniscus glued from a biconvex and biconcave lenses, the second component is a negative meniscus, which convex surface faces the space of objects, the third component is a biconvex lens, glued from a biconvex lens and negative meniscus. This lens design has a focal length f '' = 220 mm, the relative aperture is 1: 2.4. However, the disadvantage of the analogue is the low value of the modulation transmission coefficients (T) for the entire field of view: no more than 0.3 at a frequency of N = 60 mm ^-1 , which does not allow to obtain an image of low-contrast objects on the CCD matrix, as well as a large lens length, which is 1.37 f '.

Closest to the proposed lens are lenses of the type "Tair" [2], consisting of two components. The first component is made in the form of a biconvex lens and a negative lens, the second component is the meniscus, facing a concave surface to the image space and having a large thickness.

This lens design provides a 1: 3 relative aperture at a focal length of the lens of up to 300 mm. However, the disadvantage of the prototype is the low value of the modulation transmission coefficients (T), not exceeding 0.5 for a point on the axis and 0.2 for the edge of the field of view.

The objective of the invention is to improve image quality in the spectral range λ = 620 ... 850 nm by increasing the modulation transmission coefficients throughout the field of view and maintaining a small lens length, counting from the first surface of the lens to the image plane, not exceeding 1.01 focal length of the lens.

The lens contains two components located on the optical axis, the first component consists of a biconvex and negative lenses, the second component is a negative meniscus facing a concave surface to the image space, unlike the prototype, it contains an aperture diaphragm located between the components, the first component is complemented by a positive meniscus, facing the concave surface to the image space and located after its negative lens, the meniscus of the second component is glued from biconvex and double of the concave lens and has a thickness along the optical axis of at least 0.07 of the focal length of the lens, the positive lens of the first component is made of glass with a refractive index of not more than 1.5 and an Abbe number of at least 80, and the distance between the components is at least 0.13 of the focal length lens distance.

The construction of the first component containing a positive lens having a glass refractive index of not more than 1.5, an Abbe number of not less than 80 and having a special dispersion course provides correction of the secondary spectrum to 0.04 mm in the spectral range of 620 ... 850 nm, which allows to obtain good correction of chromatic aberration.

The introduction into the first component of a positive meniscus, facing a concave surface to the image space and located after its negative lens, made it possible to correct spherochromatic aberrations to values not exceeding 0.006 mm, which ensured high modulation transmission coefficients for a point on the axis.

The execution of the negative meniscus of the second component in the form of gluing from biconvex and biconcave lenses having a thickness of at least 0.07 of the focal length of the lens made it possible to correct the curvature to 0.02 mm and astigmatism to 0.013 mm for a field of view angle of 2W = 2 °.

The choice of the distance between the introduced positive meniscus and the second component of at least 0.13 of the focal length of the lens provided a short length from the first surface of the lens to the image plane, not exceeding 1.01 focal length of the lens with high image quality over the entire field of view.

The location of the aperture diaphragm between the components allows you to adjust the relative aperture of the lens.

The proposed lens operates in the spectral range:

λ = (620 ... 850) nm, has a focal length of 300 mm, the relative aperture is 1: 3. Polychromatic modulation transmission coefficients (T) for the spatial frequency N = 60 mm ^-1 at a point on the axis (y '= 0) of at least 0.8, at the edge of the field of view 2W = 2 ° of at least 0.7.

Figure 1 shows the optical scheme of the proposed lens.

Figure 2 shows the design parameters of the lenses of the lens and the characteristics of the glasses, where R is the radius of curvature of the lens surfaces, D is the distance between the lens surfaces, n _e is the refractive index of the lens glasses for the line e (λ = 546 nm), ν _e is the Abbe number for line e.

Figure 3 shows graphs of the transverse spherical aberration of the lens.

Figure 4 shows the graphs of the aberrations of wide inclined beams of the meridional section of the angle of the field of view 2W = 2 °.

Figure 5 shows a graph of the estimated polychromatic frequency-contrast characteristic (T) for a point on the axis.

Figure 6 shows a graph of the calculated polychromatic frequency-contrast characteristic (T) for a point on the edge of the field of view 2W = 3 °.

The frequency-contrast characteristics of the lens are calculated in accordance with the table of spectral efficiency coefficients of the actinic radiation flux given below.

Table λ, μm 620 670 700 750 850 FROM 0.14 1.0 0.8 0.48 0.1

The lens (figure 1) consists of two components and two filters. The first component contains a biconvex lens 1 made of SCHOTT N-PK52A glass with a refractive index n _e = 1.4985 and an Abbe number ν _e = 81.21, a biconcave lens 2 and a positive meniscus 3 facing a concave surface to the image space. The second component is made in the form of a negative meniscus facing a concave surface to the image space glued from a biconvex lens 4 and a biconcave lens 5, the meniscus thickness along the axis is 23 mm, which is 0.076 of the focal length of the lens. The distance between the components is 40.6 mm, which is 0.135 of the focal length of the lens. The lens is designed with filters 7, 8, having a total thickness of 4 mm.

The graphs of aberrations shown in FIGS. 3 and 4, as well as the graphs of a polychromatic frequency-contrast characteristic for a point on the axis and for the edge of the field of view, shown in FIGS. 5 and 6, confirm that the lens has good image quality over the entire field of view, which allows you to get an image of objects with low contrast (K = 0.1).

In the proposed lens, the choice of the design of the first component containing the first biconvex lens with a glass refractive index of not more than 1.5 and an Abbe number of at least 80, a biconcave lens and a positive meniscus facing a concave surface to the image space, the second component containing a negative meniscus facing a concave surface to the image space and glued from a biconvex and biconcave lens, and having a thickness of at least 0.7 of the focal length of the lens and the distance between the components at least 0.13 focal lengths, it was possible to obtain high values of modulation transmission coefficients over the entire field of view in the spectral range of 620 ... 850 nm and the lens length from the first surface to the image plane of 301.4 mm, which is 1.004 of the focal length of the lens.

The lens works as follows: a parallel beam of light with a field angle of 2W = 2 ° hits the first surface of the first component of the lens, and, being refracted through the surfaces of five lenses and filters, focuses in the image plane where the CCD is located.

Information sources

1. Patent RU No. 2190245 C1, publication 2002, MKP G02B 9/26, G02B 11/14.

2. Volosov DS, "Photographic optics", M., Art, 1971, S. 419-422 - prototype.

Claims (1)

A lens containing two components located on the optical axis, the first component of which consists of a biconvex and negative lenses, the second component is a negative meniscus facing a concave surface to the image space, characterized in that it contains an aperture diaphragm located between the components, the first component is complemented by a positive the meniscus facing the concave surface to the image space and located after its negative lens, the meniscus of the second component is glued from biconcave a biconcave lens and has a thickness along the optical axis of at least 0.07 of the focal length of the lens, the positive lens of the first component is made of glass with a refractive index of not more than 1.5 and an Abbe number of not less than 80, and the distance between the components is not less than 0, 13 focal lengths of the lens.

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