The telecentric lens can be used to work with CCDs

machine visions

The telecentric lens can be used to work with CCDs. The lens contains 11 single lenses, grouped into three groups of three, one and seven lenses along the ray path: of which lenses 1, 5, 8 and 11 are menisci, convex facing the object; 2 – biconcave lens; 3, 6 and 9 are biconvex lenses, and 4, 7, 9 and 10 are menisci, concavely facing the object. The focal lengths of some groups and subgroups of lenses correspond to the ratios given in the claims. EFFECT: widening the spectral range and obtaining high quality images in a single focal plane simultaneously in three spectral ranges: Δλ1 = 0.5-0.6; Δλ2 = 0.6-0.7; Δλ3 = 0.79-0.9 μm. 1 wp f-ly, 1 dwg.

The proposed invention relates to optical devices and can be used as a lens with a telecentric beam path for operation in the spectral range of 0.5 … 0.9 μm, for example, with CCD matrices.

Known wide-angle (90 °) telecentric lens (SU No. 1117570 A1, class G 02 B 13/22, publ. 07.10.84), containing nine single lenses and menisci, namely, along the beam: positive and two negative meniscus facing the convexity of the object, the aperture diaphragm, the positive and negative menisci facing the concavity of the object, two biconvex lenses and the positive and negative menisci facing the convexity of each other. The relative aperture of the objective is 1: 5, the focal length is 10 mm, and is designed for a wavelength of 546 nm.

The closest in technical essence to the proposed one is a wide-angle telecentric lens (JP 11084232 A, class G 02 B 13/04, publ. 26.03.99), containing three groups of lenses: in the first group G 1 , along the beam, biconvex lens G 1-1 and subgroup G 1-2 from a negative meniscus facing the convexity of the object and a biconcave lens, in the second group G 2 – a positive lens, in the third group G 3 – a negative lens, a positive meniscus and a biconvex lens form a subgroup G 3-1 , and gluing of a biconvex and biconcave lenses and two biconvex lenses form a subgroup G 3-2 , while the following relations are fulfilled in the lens:

(1) 0.2 <| f 1 / f 3 | <0.8

(2) 0.01 <| f / f 2 | <0.7

(3) 0.01 <| f 1 / f 1-1 | <0.5

(4) 0.7 <| f 1-2 / f 1 | <1.0

(5) | f 3 / f 3-1 | <0.6

(6) 0.5 <| f 3 / f 3-2 | <0.95

where f … are the focal lengths of the corresponding lens or objective lens groups. The lens has a large rear section (up to 100 mm), the aperture ratio is 1: 4, it operates in the visible spectral range (0.486 … 0.656 nm).

The objective of the present invention is to create a telecentric lens with an extended spectral range from 0.5 to 0.9 μm, in particular for the subranges: 0.5 ÷ 0.6; 0.6 ÷ 0.7; 0.79 ÷ 0.9 µm in a single focal plane and high image quality throughout the field.

The technical result, due to the task, is achieved by the fact that in a telecentric lens containing three groups of lenses of three, one and seven lenses, respectively, the first group G 1 includes the second negative lens, the second group G 2 – the fourth positive lens, the third group G 3– the fifth lens – a negative meniscus, convex facing the object, the sixth positive lens, the eleventh positive lens, while, unlike the known one, the first and eighth lenses are made in the form of negative menisci, convex facing the object, the second lens is biconcave, the third, the sixth and ninth are biconvex, the fourth is the meniscus, concavely facing the object, the seventh and tenth are negative menisci, convexly facing the image, the eleventh is the meniscus, concave facing the image. It is recommended that the lens adheres to the following focal length ratios (f.r.) of lens groups and subgroups:

1.2 <| f 1 / f 3 | <2.0

1.0 <| f 1 / f 1-1 | <1.8

4.0 <| f 1-2 / f 1 | <9.0

0.6 <| f 3 / f 3-1 | <0.8

0.37 <| f 3 / f 3-2 | <0.49, where

1 – d.f. group G 1 (lenses 1, 2 and 3);

3 – d.f. group G 3 (lenses 5-11);

1-1 – d.f. the first lens;

1-2 – d.f. subgroups of 2 and 3 lenses;

3-1 – d.f. subgroups of 5, 6 and 7 lenses;

3-2 – d.f. subgroups of 8, 9, 10 and 11 lenses.

The proposed implementation of the objective makes it possible to obtain the construction of a high-quality image in a single focal plane simultaneously in three spectral ranges: Δλ1 = 0.5 ÷ 0.6; Δλ2 = 0.6 ÷ 0.7; Δλ3 = 0.79 ÷ 0.9 μm.

The optical scheme is illustrated by the drawing.

The lens consists of 11 single lenses, grouped into groups G 1 of three lenses, G 2 – one lens, aperture diaphragm (AD) and group G 3 of 7 lenses. These lenses are, in the direction of the beam: 1 – negative meniscus, convex facing the object Г 1-1 ; 2 – biconcave lens; 3 – biconvex lens; while lenses 2 and 3 form a subgroup G 1-2 ; 4 – positive meniscus, concavity facing the object (G 2 ); 5 – negative meniscus facing the convexity of the object, 6 – biconvex lens, 7 – negative meniscus facing the convexity of the image, while lenses 5, 6 and 7 form a subgroup G 3-1; 8 – negative meniscus, similar to meniscus 5; 9 – biconvex lens, 10 – negative meniscus, similar to meniscus 7, 11 – positive meniscus, concavity facing the image, while lenses 8, 9, 10 and 11 form a subgroup G 3-2 . Aperture diaphragm 12 is located between groups G 2 and G 3 .

The design parameters of the lens version are as follows:

Radius Thickness Glass brand Surface diameters
R1 = 45.08 38.5
d1 = 5.0 TK21
R2 = 22.18 31.4
d2 = 8.0
R3 = -3311.0 30.8
d3 = 5.0 TF2
R4 = 27.29 28.4
d4 = 8.7
R5 = 159.96 30.4
d5 = 8.0 TF2
R6 = -41.4 31.1
d6 = 8.3
R7 = -35.4 28.6
d7 = 8.0 OK4
R8 = 25.59 29.1
d8 = 25.0
R9 = 0.0 11.9
d9 = 13.7
R10 = 113.18 19.3
d10 = 5.0 K8
R11 = 26.06 21.2
d11 = 2.0
R12 = 30.27 23.5
d12 = 10.0 OK4
R13 = -24.77 25.0
d13 = 1.9
R14 = -22.8 25.0
d14 = 5.0 TF2
R15 = -35.08 28.0
d15 = 10.0
R16 = 218.3 31.7
d16 = 5.0 K8
R17 = 32.66 32.9
d17 = 3.0
R18 = 41.86 35.4
d18 = 12.0 OK4
R19 = -29.51 36.0
d19 = 10.1
R20 = -32.06 32.9
d20 = 5.0 TC21
R21 = -73.62 35.3
d21 = 10.0
R22 = 137.72 37.8
d22 = 8.0 K8
R23 = 610.9 38.0

The focal lengths of the lens groups and their ratios for this embodiment are as follows:

1 = -115.9 | f 1 : f 3 | = 1.53
3 = 75.07 | f 1 : f 1-1 | = 1.56
1-1 = -73.79 | f 1-2 : f 1 | = 6.1
1-2 = 709.2 | f 3 : f 3-1 | = 0.67
3-1 = 112.02 | f 3 : f 3-2 | = 0.44
3-2 = 170.14

The parameters of this version of the lens:

– working spectral range 0.5 ÷ 0.9 μm;
– focal length 40.0 mm;
– posterior focal segment 25.2 mm;
– angular field of view 54 °
– linear field in image space ⊘40 mm;
– relative aperture 1: 6.0.

The lens is designed to work with a CCD receiver. It provides an image of objects to the CCD receiver. Therefore, it is calculated taking into account the installation of a protective glass of an optoelectronic unit, a filter glass and a photodetector with a thickness of 5 mm, 3 mm and 0.4 mm, respectively, in the gap S F ‘ .

The image quality of a lens is characterized by its MTF.

So, for a frequency of N = 70 ln / mm, the image contrast is of the order of:

Range, μm
0.5 ÷ 0.6 0.6 ÷ 0.7 0.79 ÷ 0.9
Mer. Sag. Mer. Sag. Mer. Sag.
Point on axis 0.67 0.6 0.5
Middle of the field of view 0.58 0.64 0.58 0.58 0.51 0.55
Edge of the field of view 0.43 0.56 0.38 0.53 0.42 0.46

1. Telecentric lens containing three groups of lenses: three, one and seven lenses along the beam, of which the first group G 1 includes the second negative lens, the second group G 2 – the fourth positive lens, the third group G 3 – the fifth lens – negative meniscus facing the convexity of the object, the sixth positive lens, the eleventh positive lens, characterized in that the first and eighth lenses are negative meniscus facing the convexity of the object, the second is biconcave, the third, sixth and ninth are biconvex, the fourth is the meniscus, facing concave to the object, the seventh and tenth are negative menisci, convex facing the image, the eleventh is the meniscus, concave facing the image.

2. Telecentric lens according to claim 1, characterized in that the following ratios are fulfilled in it:

1.2 <| f 1 / f 3 | <1.8,

1.0 <| f 1 / f 1-1 | <2.0,

4.0 <| f 1-2 / f 1 | <8.0,

0.6 <| f 3 / f 3-1 | <0.8,

0.2 <| f 3 / f 3-2 | <0.49,

where f 1 is the focal length (f.r.) of the group G 1 (lenses 1, 2 and 3);

3 – d.f. group G 3 (lenses 5-11);

1-1 – d.f. the first lens G 1-1 ;

1-2 – d.f. subgroups G 1-2 of 2 and 3 lenses;

3-1 – d.f. subgroups G 3-1 of 5, 6 and 7 lenses;

3-2 – d.f. subgroups G 3-2 of 8, 9, 10 and 11 lenses.

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By aamritri

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