RU2400786C2 - Infrared telescope for far infrared spectrum with remote exit pupil and two magnification power values - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: telescope has an exit pupil position which does not change when magnification is changed outside the eyepiece and an entrance pupil which is superposed with a first lens during high magnification. The telescope has a positive objective lens which includes a first positive, second and third negative menisci whose concave surfaces face the plane of the exit pupil, and an eyepiece which includes a fourth positive meniscus whose convex surface faces the exit pupil, and a fifth fixed positive meniscus whose concave surface faces the plane of the exit pupil. The third and fourth menisci have two fixed positions each and small displacements in these positions. Parameters of the telescope are related through relationships given in the formula of invention.

EFFECT: simple design, reduced cost price, high transmission coefficient owing to fewer lenses in the system, reduced internal background noise and reduced impact of Narcissus effect.

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Description

The invention relates to the field of optical instrumentation, namely to infrared (IR) telescopic (afocal) systems with a change of magnification and can be used in optical systems of thermal imagers.

In thermal imagers, changing the angular magnification of the telescopic system allows you to ensure at least two magnifications when observing the space of objects: at low magnification and correspondingly wide field, objects of observation are searched; at high magnification and a narrow field - recognition of objects.

Known optical systems of infrared telescopes for the far infrared region of the spectrum in which the change of magnification is carried out by moving the components along the optical axis (EPO No. 0278777, 1988. Dual magnification infra-red telescope). The optical system of this telescope, providing a twofold change in magnification, contains 10 lenses. The main disadvantage is the large number of lens components, which reduces the transmittance of radiation, the presence of spurious glare from a large number of refracting surfaces, the complexity of the design and high cost.

An infrared telescope is proposed for the far infrared region of the spectrum with a remote exit pupil and two magnifications that differ by no less than two times, having the position of the exit pupil behind the telescope eyepiece and the entrance pupil unchanged when the magnification changes, combined with a larger magnification with the first telescope lens . The telescope contains a positive lens, including the first positive, second negative and third negative menisci located at a small distance relative to each other along the rays, facing concave surfaces to the plane of the exit pupil, and an eyepiece including the fourth lens and the fifth stationary component along the rays of the telescope. The third negative meniscus and the fourth lens for changing magnification have two fixed positions on the optical axis, in which the distances between the corresponding vertices of the refracting surfaces of the third negative meniscus and the fourth lens differ, as well as small movements along the optical axis in these fixed positions, the second negative the meniscus is made of a material with a larger dispersion value than that of the material of the first positive meniscus. All refracting surfaces are spherical. The ratio of the radii of curvature of the second surface of the fourth lens and the first surface of the first positive meniscus in absolute value is not less than 0.2. In the telescope, the ratio is:

where f ₁ , f ₂ - the optical power, respectively, of the first positive, second negative menisci.

The fourth lens is made in the form of a positive meniscus facing a convex surface to the plane of the exit pupil. The fifth fixed component is made in the form of a single lens having the shape of a positive meniscus facing a concave surface to the plane of the exit pupil. The eyepiece lenses are made of the same brand of material, with the following relationships:

where Ф ₄ , Ф ₅ are the optical forces of the fourth and fifth positive menisci, respectively;

R ₉ , R ₁₀ - the radii of the first and second along the rays of the refracting surfaces of the fifth positive meniscus;

- удаление выходного зрачка от последней поверхности телескопа.

- removal of the exit pupil from the last surface of the telescope.

The proposed infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications allows you to maintain higher technical characteristics while maintaining the angular magnifications of the telescope and diffraction image quality: simplify the design, reduce cost, increase transmittance by reducing the number of lenses in the system, reduce internal background noise and reduce the effect of the Narcissus effect by reducing spurious glare from fewer refracting surfaces These, especially from the latter along the rays of the refracting surfaces.

Higher technical characteristics of the proposed infrared telescope for the far infrared spectrum with a remote exit pupil and two magnifications are provided by a new set of distinctive features:

- the fourth lens is made in the form of a positive meniscus facing a convex surface to the plane of the exit pupil,

- the fifth fixed component is made in the form of a single lens having the shape of a positive meniscus facing a concave surface to the plane of the exit pupil,

- the eyepiece lenses are made of the same brand of material, while the above relations (2) hold.

The implementation of the fifth fixed component in the form of a single lens, having the shape of a positive meniscus, facing a concave surface to the plane of the exit pupil, allows to reduce the number of lenses in this component and thereby simplify the design, reduce costs, and increase transmittance.

позволяет при уменьшении количества линз в системе сохранить высокую степень коррекции полевых аберраций и сохранить дифракционное качество изображения для двух значений угловых увеличений телескопа.The fourth lens in the form of a positive meniscus facing a convex surface to the plane of the exit pupil, together with the ratio

when reducing the number of lenses in the system, it is possible to maintain a high degree of field aberration correction and to preserve the diffraction image quality for two values of the angular magnifications of the telescope.

The orientation of the fourth and fifth menisci in the above way allows you to maintain a high degree of correction of aberrations of wide beams of rays for two values of the angular magnifications of the telescope.

позволяет уменьшить эффект Нарцисса от последней поверхности телескопа, т.к. плоскость приемника в обратном ходе, отразившись от десятой поверхности, проецируется во входной зрачок фокусирующего объектива, не сопряженный оптически с задней фокальной плоскостью фокусирующего объектива (плоскостью приемника).Ratio

reduces the effect of Narcissus from the last surface of the telescope, because the plane of the receiver in reverse, reflected from the tenth surface, is projected into the entrance pupil of the focusing lens, not optically conjugated with the rear focal plane of the focusing lens (plane of the receiver).

позволяет уменьшить эффект Нарцисса и паразитные блики от последнего мениска телескопа, обеспечив тем самым высокое качество изображения.Ratio

reduces the effect of Narcissus and spurious glare from the last meniscus of the telescope, thereby ensuring high image quality.

The authors do not know the optical systems of infrared telescopes for the far infrared region of the spectrum with a remote exit pupil and two magnifications that differ by at least two times, having the position of the exit pupil behind the telescope’s eyepiece and the entrance pupil unchanged when the magnification changes, combined at a larger magnification with the first telescope lens, having features similar to those distinguishing the proposed system from the prototype, therefore this infrared telescope system for the far infrared region of the spectrum with an exit pupil and two magnifications, it has significant differences.

The proposed invention is illustrated by the following graphic materials:

Figa - optical diagram of an infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications for a narrow field;

Fig.1b is an optical diagram of an infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications for a wide field;

Figa - frequency-contrast characteristics (frequency response) of an infrared telescope (narrow field);

Fig.2b - frequency response of the infrared telescope (wide field);

Figa - distortion of an infrared telescope (narrow field);

Figb - distortion of the infrared telescope (wide field).

On figa and 1b shows the proposed optical scheme of the infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications for a narrow and wide fields in the space of objects.

The telescope contains five single lenses 1-5 located along the rays. The exit pupil of the telescope is located along the rays after the last lens 5. In this case, the first positive meniscus 1, the second negative meniscus 2 and the third negative meniscus 3 are turned by concave surfaces to the plane of the exit pupil and form a positive lens 6, and the fourth positive meniscus 4, facing a convex surface to the plane of the exit pupil, and the fifth positive meniscus 5, facing a concave surface to the plane of the exit pupil, form a positive eyepiece 7. The third negative meniscus and four To ensure the change in magnification, two fixed positions on the optical axis have each positive meniscus, in which the distances between the corresponding vertices of the refracting surfaces of the third negative meniscus and the fourth lens differ, as well as small movements along the optical axis in these fixed positions, the second negative meniscus from a material with a larger dispersion value than that of the material of the first positive meniscus. All refracting surfaces are spherical. The ratio of the radii of curvature of the second surface of the fourth meniscus and the first surface of the first positive meniscus in absolute value is not less than 0.2. In the optical system of the telescope, the above relations (1) and (2) take place. With the arrangement of the lenses in accordance with figa in the telescope provides a narrow field, and in accordance with figb - a wide field. The entrance pupil in the position of the lenses providing a narrow field coincides with the first meniscus. The position of the exit pupil and its size remain constant both in a narrow and in a wide field.

Infrared radiation coming from each point of a distant object, passing sequentially through lenses 1-5 of the telescope, leaves the exit pupil of the telescope in parallel beams. Moreover, in the fixed positions of the lenses 3 and 4, corresponding to the scheme shown in figa, provides a narrow field of view in the space of objects (i.e., a larger angular increase of the telescope), and in the fixed positions corresponding to the circuit shown in fig.1b , - a wide field of view in the space of objects (i.e., a smaller angular increase in the telescope).

To carry out thermal compensation under real operating temperatures and to refocus to a finite distance to the objects of observation, small shifts of components 3 and (or) 4 along the optical axis in fixed positions are used.

As a specific example of execution, Table 1 shows an example implementation of an infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications.

Table 1 Parameters of an example implementation of an infrared telescope for the far infrared spectrum with a remote exit pupil and two magnifications that differ in size by a factor of three (γ ₁ = 8.54 ^x ; 2ω ₁ = 3 ° 49 ^// ; γ ₂ = 2.83 ^x ; 2ω ₂ = 10 ° 30 ^/ D ′ = 10.2 mm) The name or number of the element in accordance with figa and 1B The number of lenses in accordance with figa and 1B Relative optical power The distance along the optical axis in accordance with figa The distance along the optical axis in accordance with figb Lens material Entrance pupil 0 -0.48 6 one 2,210 0,034 0,034 Ge 2 -0.249 0.277 0.371 Znse 3 -4.143 0.320 0.059 Ge 7 four 5,779 0.059 0.225 Ge 5 3,720 0.095 * 0.095 * Ge * Distance to the exit pupil.

The following notation is accepted in the table:

γ ₁ - angular increase of the telescope at the positions of the lenses corresponding to the scheme in figa (narrow field of view);

2ω ₁ is the angular field in the space of objects with increasing γ ₁ ;

γ ₂ is the angular magnification of the telescope at the positions of the lenses corresponding to the scheme in figb (wide field of view);

2ω ₂ - the angular field in the space of objects with increasing γ ₂ ,

D ′ is the diameter of the exit pupil of the telescope.

The relative optical power of the telescope lenses and the distances along the optical axis between the lenses are indicated on the basis of the following normalization: the equivalent focal length f of the telescope system with a narrow field of view, equipped with an additional lens having a focal length of 25 mm, mounted after the lens so that its entrance pupil coincides with the exit pupil of the telescope is equal to minus 1.

As follows from table 1, in a specific example of the implementation of the infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications, the distance from the last lens to the exit pupil of the telescope is 0.095 | f |, the distance to the entrance pupil in a telescope with a narrow field is 0 , i.e. the entrance pupil in this position coincides with the first lens of the telescope. Wherein

which satisfies condition (2), and the ratio of the radii of curvature of the second surface of the fourth meniscus and the first surface of the first positive meniscus in absolute value is 0.29, which is more than 0.2. The total length along the optical axis from the first surface to the exit pupil of the telescope is 0.92 | f |. The angular magnifications of the telescope at the positions of the lenses corresponding to figa and 1b differ by 3 times.

Exact values of optical forces, radii of refractive surfaces and thicknesses along the optical axis for specific values of refractive indices and specific values of the angular magnifications of the infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications that differ in size by at least two times, having the position of the exit pupil, unchanged when changing the magnification, behind the telescope eyepiece and the entrance pupil, combined at higher magnification with the first lens of the telescope, are installed Artney optimization by the least squares method, which is a part of all modern software for optical design.

Image quality analysis of an example implementation of an infrared telescope for the far infrared region with a remote exit pupil and two magnifications was carried out in the Zemax program for the following values: γ ₁ = 8.54 ^x ; 2ω ₁ = 3 ° 49 ^// (narrow field); γ ₂ = 2.83 ^x ; 2ω ₂ = 10 ° 30 ^/ (wide field); D ′ = 10.2 mm, together with an ideal lens having a focal length of 25 mm, mounted behind the telescope. The frequency response curves for the indicated implementation example are shown in table 2, in FIG. 2a (for a narrow field) and in table 3, in FIG. 2b (for a wide field).

table 2 The frequency response curve of an example implementation of an infrared telescope for the far infrared region with a remote exit pupil and two magnifications (narrow field - γ ₁ = 8.54 ^x ; 2ω ₁ = 3 ° 49 ^// ; D ′ = 10.2 mm) Frequency, mm ^-1 Differ. Point on axis ω = 1 ° ω = 1 ° 55 ^/ / m s m s 10.0 0.716 0.692 0.673 0.695 0.672 0.658 20,0 0.446 0.414 0.389 0.426 0.362 0.380 30,0 0.212 0.186 0.169 0.196 0.151 0.188 40,0 0,053 0,049 0,047 0,052 0,041 0,048 50,0 0.002 0.002 0.002 0.002 0.002 0.002

Table 3 The frequency response curve of an example implementation of an infrared telescope for the far infrared spectrum with a remote exit pupil and two magnifications (wide field - γ ₂ = 2.83 ^x ; 2ω ₂ = 10 ° 30 ^// ; D ′ = 10.2 mm) Frequency, mm ^-1 Differ. Point on axis ω = 3 ° 30 ^/ / ω = 5 ° 15 ^/ m s m s 10.0 0.716 0.614 0.593 0.644 0.582 0.662 20,0 0.447 0.328 0,305 0.370 0.298 0.409 30,0 0.214 0.189 0.178 0,200 0.170 0.196 40,0 0,054 0,054 0,052 0,053 0,050 0,047 50,0 0.002 0.002 0.002 0.002 0.002 0.002

In tables 2 and 3, the values of the contrast transfer coefficients are given for a point on the axis and for two values of the angles ω corresponding to the edge of the field of view and zone, both for the meridional (m) and sagittal (s) sections. Contrast transmission coefficients are indicated in relative units for spatial frequencies in the range from 0 to 50 mm ^-1 , assigned to the focal plane of an ideal lens with a focal length of 25 mm, located along the rays behind the exit pupil of the infrared telescope.

On figa and 2b along the abscissa axis the indicated values of spatial frequencies are plotted, in mm ^-1 ; along the ordinate axis - the values of the contrast transfer coefficients, rel. units The frequency response graphs are presented for a point on the axis (designation “O”) and for points on the edge of the field of view (designation “ω ₁ ” or “ω ₂ ”) for both meridional (m) and sagittal sections (s). For the remaining points of the field, the frequency response values are located between the corresponding values for the points on the axis and on the edge of the field and the graphs of such frequency response curves are not shown in Figures 2a and 2. For comparison, Figures 2a and 2b also show the frequency response of the non-aberrational lens (the designation is “Diphr. )

As follows from tables 2, 3 and FIGS. 2a and 2b, the optical system of the infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications in each of the fixed positions of the lenses provides image quality close to diffraction.

Tables 4, 5 show the relative distortion values of an example implementation of an infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications, and Figures 3a and 3b show the corresponding distortion graphs. The angles ω, rel. units, and on the abscissa axis - relative distortion,%.

Table 4 Distortion of an example implementation of an infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications (narrow field - γ ₁ = 8.54 ^x ; 2ω ₁ = 3 ° 49 ^// ; D ′ = 10.2 mm) ω, rel. units Relative distortion,% 0.2 0.13 0.4 0.54 0.6 1.23 0.8 2.25 1,0 3.65

Table 5 Distortion of an example implementation of an infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications (wide field - γ ₂ = 2.83 ^x ; 2ω ₂ = 10 ° 30 ^// ; D ′ = 10.2 mm) ω, rel. units Relative distortion,% 0.2 -0.19 0.4 -0.78 0.6 -1.75 0.8 -3.12 1,0 -4.89

The distortion value in the example of the implementation of the infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications both in the position corresponding to the narrow field and in the position corresponding to the wide field does not exceed 5%, which is acceptable for using the proposed telescope in optical systems of thermal imagers containing scanning elements installed in the exit pupil of the telescopic system.

A comparative assessment of the quality of eliminating the effect of Narcissus in the proposed system and in the prototype can most simply be carried out according to the criterion "YNI", the calculation results of which are shown in table 6.

Table 6 The value of the criterion "YNI" Prototype An example implementation of an infrared telescope for the far infrared region with a remote exit pupil and two magnifications Surface number along the rays Yni Surface number along the rays Yni one 17.20516 one 16.30602 2 -6.66010 2 -9.67674 3 -11.65486 3 -12.56690 four -9.55891 four -9.69975 5 -3.73375 5 -4.52050 6 -1.31146 6 -1.43445 7 1.25610 7 0.49304 8 -0.24876 8 -0.14683 9 -0.82552 9 1.19910 10 -0.49799 10 0.52096 eleven 1.09779 12 0.81448 Sum of absolute values 54.8 Sum of absolute values 56.6

A greater value of the criterion "YNI" with fewer refracting surfaces indicates a decrease in the effect of the Narcissus effect in the implementation example compared to the prototype.

Thus, the proposed infrared telescope for the far infrared spectrum with a remote exit pupil and two magnifications, having a combination of these distinctive features, in comparison with the prototype allows to provide the following technical advantages: simplified design, lower cost, higher transmittance by reducing the number of lenses in the system, reducing internal background noise and reducing the effect of the Narcissus effect.

Implementation of the technical advantages of the present invention allows its use in optical systems of thermal imagers, including those containing scanning elements installed in the exit pupil of the telescopic system.

Literature

1. EPO No. 0278777, 1988, Dual magnification infra-red telescope.

Claims (1)

Infrared telescope for the far infrared region of the spectrum with a remote exit pupil and two magnifications that differ by at least two times the size, having the position of the exit pupil behind the telescope’s eyepiece and the entrance pupil unchanged when the magnification changes, combined with a larger magnification with the first telescope lens, containing a positive lens, including located at a small distance relative to each other along the rays of the first positive, second negative and third negative menisci facing concave surfaces to the plane of the exit pupil, and the eyepiece including the fourth lens along the rays of the telescope and the fifth stationary component, while the third negative meniscus and the fourth lens for changing magnification have two fixed positions on the optical axis, in which the distances between the corresponding vertices of the refracting the surfaces of the third negative meniscus and the fourth lens differ from each other, as well as small movements along the optical axis in these fixed positions, the second negative meniscus is executed ene of a material with larger size dispersion than the material of the first positive meniscus all refracting surfaces are spherical, the ratio of the radii of curvature of the second surface of the fourth lens and the first surface of the first positive meniscus absolute value is not less than 0.2, and the following relation

where f ₁ f ₂ - the optical forces, respectively, of the first positive and second negative menisci,
characterized in that the fourth lens is made in the form of a positive meniscus facing a convex surface to the plane of the exit pupil, the fifth fixed component is made in the form of a single lens having the shape of a positive meniscus facing a concave surface to the plane of the exit pupil, the eyepiece lenses are made of the same brand of material, the following relations hold:

where Ф ₄ , Ф ₅ are the optical forces of the fourth and fifth positive menisci, respectively;
R ₉ , R ₁₀ - the radii of the first and second along the rays of the refracting surfaces of the fifth positive meniscus;

- removal of the exit pupil from the last surface of the telescope.

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