RU2031421C1 - Objective for ir region of spectrum - Google Patents

Abstract

FIELD: optics. SUBSTANCE: objective has two positive germanium lenses mounted for movement along optical axis. First one is convex-concave having first spherical and second aspherical surfaces, second one is convex-flat or convex-concave having first aspherical and second flat or spherical surfaces. Lenses are mounted for simultaneous or successive movement till interlens distance and rear focal section are set in agreement with expansions given in description of invention. Aspherical surfaces are defined by proper equations. EFFECT: improved optical characteristics of objective. 2 cl, 1 dwg

Description

 The invention relates to optical instrumentation, namely to lens lenses for the infrared region of the spectrum, and can be used in observation and identification devices that record infrared radiation in the field of transparency of germanium, from which the lens is made.

 Known lens [1], intended for use in the infrared region of the spectrum. The lens consists of two meniscus-shaped lenses, with a parallel plate mounted behind the second lens.

 The disadvantages of the lens include the fact that it consists of three optical components, which complicates the design, reduces transmittance, increases the overall and weight characteristics of the lens.

 The closest in technical essence to this invention is a lens for the infrared spectrum [2], containing two mounted with the possibility of movement along the optical axis of the germanium lenses, the first of which is convex-concave, having a first spherical and second aspherical surface, and the second convex-flat or convex-concave, having a first aspherical and a second flat or spherical surface. However, the quality of the image provided by the lens does not meet the requirements of modern infrared instrument making, which is most significantly manifested when the lens is focused at different distances to the imaged object. The focus of the Irtal-4 lens is performed by simultaneously and equally moving both lenses along the optical axis at a constant distance between the lenses, as a result of which the transverse aberrations determining the width of the scattering function of the Irtal-4 lens at a point on the axis are 0.1 mm , and at the edge of the field of view reaches 0.2 mm.

 The aim of the invention is to reduce aberrations in a fixed plane of the image in the process of focusing the lens at various distances to the imaged object throughout the field of view.

 The goal is achieved by the fact that in the known lens design for the infrared region of the spectrum, containing two mounted with the possibility of moving along the optical axis germanium lenses, the first of which is a convex-concave meniscus having a first spherical and second aspherical surface, and the second is convex-flat or a convex-concave lens having a first aspherical and a second flat or spherical surface, the lenses are mounted with the possibility of simultaneous or sequential movement before installing the lens states d and the posterior focal length S 'in accordance with the expressions below.

 The drawing shows the design of the lens for the infrared region of the spectrum.

The lens comprises a first convex-concave lens 1 from Germany having a first 1 'convex spherical and a second 1 "concave aspherical surface, a second convex-flat or convex-concave lens 2 from Germany, having a first 2' convex aspherical surface and a second 2" flat or spherical surface. Lenses 1 and 2 are installed with the possibility of simultaneous or sequential movement (indicated by arrows above lenses 1 and 2) along the optical axis 3 until the lens distance 4 (d) and the rear focal length 5 (S ') are set in accordance with the expressions d = 0.98f ^' + 7100 S ^-1.15
S '= 0.3537 + 1600 S ^-0.96 , where f' is the focal length of the lens (not shown in the drawing), equal to 49-51 mm; S is the distance 6 from the subject 7 to the first 1 'spherical surface of the first convex-concave lens 1, 8 is the fixed image plane, the second concave aspherical surface 1 "of the first lens 1 is made according to the equation
z ² + y ² = a ₁ x + a ₂ x ² + a ₃ x ³ + ... + a _n x ⁿ , where x, y, z are the coordinates (not shown) of the concave aspherical surface 1 "; x is the axial coordinate that coincides with the optical axis 3 of the lens; a ₁ , a ₂ , a ₃ ... a _n are constant coefficients that determine the shape of the second concave aspherical surface 1 ", and n> 2, and the coefficient a ₂ has the value a ₂ <-1, which characterizes the execution of a concave aspherical surface 1 "of the lens 1 in the form of a deformed ellipsoid of revolution, the first convex aspherical surface 2 'of the second lens 2 from Germany is made according to ur vneny
z ² + y ² = b ₁ x + b ₂ X ² + b ₃ x ³ + ... + b _n x ⁿ , where x, y, z are the coordinates (not shown) of the convex aspherical surface 2 '; x is the axial coordinate coinciding with the optical axis 3 of the lens; b ₁ , b ₂ , b ₃ , ..., b _n are constant coefficients that determine the shape of the concave aspherical surface 2 ', and n> 2, and the coefficient b ₂ has the value b ₂ > 1, which characterizes the implementation of the convex aspherical surface 2 'lens 2 in the form of a deformed hyperboloid of revolution.

PRI me R 1. The lens consists of lenses 1 and 2 of Germany. The first 1 'surface of the lens 1 is made convex spherical with a radius of curvature of 135, 83 mm. The second 1 "surface of the lens 1 is concave aspherical, representing a deformed ellipsoid of revolution
z ² + y ² = 416.8x - 13.842x ² - 0.2448x ³ -
- 0.0185x ⁴ - 0.000843x ⁵ ,
a ₂ = -13.842 <- 1.

The first surface 2 'of lens 2 is made convex aspherical, representing a deformed rotation hyperboloid:
z ² + y ² = 287.58x + 4.0886x ² - 1.68287x ³ +
+ 0.2215x ⁴ - 0.000787x ⁵ ,
b ₂ = 4.0886> 1
The second surface 2 "of lens 2 is made flat. The lens has the following characteristics: relative aperture 1: 0.7, angular field of view 18 °, focal length f '= 49.95 mm. When focusing the lens at various distances from subject 7 to the first spherical surface 1 'of the first convex-concave lens 1, varying from 1 to infinity, the magnitude of the inter-lens distance d and the rear focal segment S' varies from 51.50 to 49.00 mm and from 29.00 to 26.83 mm, respectively.

 Moving lenses is possible both simultaneous and sequential. The magnitude of the measured transverse aberrations, which determine the width of the distance function for the manufactured lens of the indicated design at a point on the axis, was 0.03 mm and 0.07 mm at the edge of the image field, which was more than two times less than the lens aberrations of the prototype.

 Thus, this design of the lens for the infrared region of the spectrum allows one to reduce aberrations in the fixed plane of the image both at a point on the axis and at the edge of the image field, in the process of focusing the lens at various distances to the imaged object.

Claims (2)

1. LENS FOR IR-AREA OF THE SPECTRUM, containing two positively mounted germanium lenses that can be moved, the first of which is the meniscus facing concavity to the image, and the second is a convex flat or convex lens, the lens surfaces facing each other are aspherical, characterized the fact that the concave aspherical surface of the first lens is made according to the equation
z ² + y ² = a ₁ x + a ₂ x ² + a ₃ x ^{3 _{+ ... + a n · x n}} ,
and the first convex aspherical surface of the second lens according to the equation
z ² + y ² = b ₁ x + b ₂ x ² + b ₃ x ³ + b _g x ⁿ ,
where x, y, z are the coordinates of aspherical surfaces;
x is the axial coordinate;
a ₁ , a ₂ , a ₃ , a _n , b ₁ , b ₂ , b ₃ ... b _n are constant coefficients, and a ₂ <- 1 and b ₂ > 1. 2. The lens according to claim 1, characterized in that the lenses are mounted with the possibility of simultaneous or sequential movement, and the distance between the lenses d and the magnitude of the rear focal segment S ^{1 are} determined from the relations
d = 0.98f ¹ + 7100S ^{- 1 , 1 5} ;
S ¹ = 0.53f ¹ + 1600S ^{- 0 , 9 6} ,
where f ¹ is the focal length of the lens, equal to 49 - 51 mm;
S is the distance from the subject plane to the first surface of the first lens.

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