EP2606392A1

EP2606392A1 - Wide open wide-angle lens

Info

Publication number: EP2606392A1
Application number: EP11745957.8A
Authority: EP
Inventors: Hildegard Ebbesmeier; Thomas Steinich
Original assignee: Jos Schneider Optische Werke GmbH
Current assignee: Jos Schneider Optische Werke GmbH
Priority date: 2010-08-20
Filing date: 2011-08-11
Publication date: 2013-06-26
Also published as: WO2012022673A1; CA2808950A1; KR20130047745A; DE102010035034B3; CN103097934A; US20130188265A1; JP2013536467A

Abstract

The invention relates to a wide open wide-angle lens for digital image acquisition, comprising five lenses, that is, as seen looking from the object side, which is from the left, a first negative meniscus lens (112), a second positive lens (118), a third positive lens (126), a fourth negative lens (130), and a fifth positive meniscus lens. A diaphragm (122) is disposed between the second lens (118) and the third lens (126). At least three surface areas in front of the diaphragm and three surface areas behind the diaphragm are designed as aspherical surfaces. However, additional surfaces can also have an aspherical design. Given the extremely compact design and the outstanding optical properties, the proposed wide open wide-angle lens is suitable as an interchangeable lens for hybrid cameras.

Description

High open wide angle lens

description

Field of the invention

The invention relates to a high open wide angle ektiv for digital image recording for photographic and industrial applications.

State of the art

In addition to digital SLR cameras, there is an increasing interest in digital cameras without mirrors, but with similar properties in terms of imaging quality and accessories, especially with regard to the possibility of using interchangeable lenses for special tasks.

The absence of the mirror brings the systems above all a size advantage over SLR cameras. The model1-sized mirrorless cameras are already approaching those of large compact cameras.

Digital cameras with interchangeable lenses, but without mirrors are often referred to as "hybrid camera". To realize various special uses of such cameras u. a. also requires interchangeable lenses as compact as possible.

A wide-angle lens for digital image acquisition is described, for example, in US Pat. No. 7,239,457 B2. This farewell The kelobjektiv is suitable for shooting with a field angle in the range between 40 ° and 50 °. It has five or six lenses, with the third and fourth lenses cemented together. One of the application proper property of the lens described is, for example, by means of a prism by 90 ° deflected beam path behind the front lens. As a result, it is not suitable as a hybrid for hybrid cameras. Furthermore, it has a very large overall length.

Classic Wide Angle Retrofocus Obj ective, such. B. US 5,631,780, consist of a plurality of spherical lenses, here z. B. 10 lenses, and have a length of about 70 to 100 mm. Aspherical surfaces are used only to a very small extent, here for example only two surfaces.

For example, US 2009/0009887 A1 describes a wide-angle lens with only five lenses, wherein, viewed from the object side, the third and fourth lenses form a doublet. In this case, at least one of the five lenses has an aspherical surface on the object side, and at least one of the five lenses has an aspherical surface on the image side. In addition, a total of at least three of the surfaces of the five lenses are aspherical.

Another document (US 2003/0174410 Al) discloses a wide-angle lens (with fixed focal length), which also includes five lenses that represent four lens groups. Again, the third and fourth lens, viewed from the object side, a doublet. All lens groups, with the exception of the doublet, are single lenses, each of the individual lenses having an aspherical surface.

task

The object of the invention is to provide a high-open Weitwin kelobjektiv, which is characterized by a very compact design and by a very good imaging quality net.

solution

This object is solved by the inventions having the features of the independent claim. Advantageous developments of the inventions are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into the content of this specification.

The invention relates to a Weitwinkelob ektiv for the digital image acquisition, which in the order given, viewed from the object side, comprising the following elements:

a) a first negative meniscus lens,

wherein the convex surface of the meniscus lens faces the object side;

b) a second positive lens,

wherein the more curved convex surface of the lens faces the object side;

c) an aperture;

d) a third positive lens,

wherein the more curved convex surface of the lens faces away from the object side;

e) a fourth negative lens;

f) wherein the third positive lens and the fourth negative lens are cemented together; and

g) a fifth positive meniscus lens, wherein the convex

Surface of the meniscus lens facing away from the object side; h) wherein the wide-angle lens has no further lenses; i) wherein the surface of the second lens facing the object has an aspheric surface;

j) wherein at least three lens surfaces are formed on the object side in front of the diaphragm and at least three lens surfaces on the image side behind the diaphragm as an aspherical surface; and k) wherein the refractive indices and Abbe numbers rid v <j of Linsenma ^¬ terialien satisfy the conditions according to the following table, all of these conditions must be met simultaneously:

, and

1) wherein the focal length of the first lens has ektivs a value in the region of the loading ^¬ -1,0fachen -1,2fachen to the total focal length of the Weitwinkelob.

The proposed Weitwinkelob ektiv is suitable for the

Use in conjunction with image sensors up to an image circle diameter of 30 mm. In particular, they can be used in the photographic field for APS-C ("Advanced Photo System Classic") sensors and Micro-Four-Third sensors.The sensor size in APS-C is about 23, 6 x 15, 8 mm (approx ei ^{¬ an} aspect ratio of 3: 2 corresponds).

The proposed lens with a focal length of 16 mm and aperture numbers of 2.8 and 2.2 is suitable for Bildkreis ^¬ diameter up to 30 mm. The lens with a focal length of 12 mm and a f-number of 2.4 is intended for image circle diameter up to 21.7 mm.

The obj ektseitige angle of the lens is greater than 80 °, in particular, it is 85 °. The significantly klei ^¬ nere image-side angle (main steel angle falling on the chip level) is at most 20 ° and is required when a ^¬ set of sensors with microlenses in order to avoid loss of brightness.

The selection of glass grades with higher refractive indices (n _d ^ 1,8) for the first four lenses favors the achievement of a extremely compact overall system while maintaining the very good correction state (which corresponds to a high imaging performance).

Due to its extremely compact design and its outstanding optical properties, the proposed high-open wide-angle lens is also particularly suitable as an interchangeable lens for the so-called "hybrid cameras".

In an advantageous development of the objective, the second positive lens and / or the third positive lens and / or the fourth negative lens of the objective is designed as a meniscus lens.

It is also advantageous that the image can be focused by displacing the entire objective along the optical axis, the distances between the lenses of the objective remaining constant, and changing only the distance between the last surface of the fifth lens and the image sensor becomes.

The focus on different distances can be done except by the said total displacement of the lens in addition by changing the first air space after the aperture, so the distance between the diaphragm and the third positive lens. The latter enables optimal imaging performance over a large magnification range.

The air distance behind the first lens should be at least 0.6x the focal length of the lens, while the focal distance behind the last lens surface in the image-wise direction should be at least 1.25 times the focal length of the lens.

It is also favorable if the fourth lens has a negative is niskuslinse, wherein the concave surface of the lens faces the object side.

It is also advantageous if the first lens has two aspherical surfaces. This is to correct distortion, astigmatism and field curvature.

It is also favorable if the fifth lens has two aspherical surfaces. This is for the correction of field-dependent aberrations and reduces the image-side

Image angle compared to the e ect-side angle of view.

Advantageously, the ektseitige surface of the second lens should be formed as an aspheric to ensure the correction of the spherical aberration. An additional aspheric surface on the image-side surface is useful to achieve higher initial openings than k = 2, 8 (eg, k = 2.2). It is also advantageous if the obj ektseitige surface of the third lens has an aspheric surface. This serves to correct pupil-dependent image errors.

In a further advantageous embodiment, it is favorable that the ratio of the Abbe number of the third lens to the Abbe number of the fourth lens is a value greater than or equal to 1.5.

Further details and features will become apparent from the following description of preferred embodiments in conjunction with the subclaims. In this case, the respective features can be implemented on their own or in combination with one another. The possibilities, the task are not limited to the embodiments. For example, area information always includes all - not mentioned - intermediate values and all imaginable subintervals.

The embodiments are shown schematically in the figures. The same reference numerals in the individual figures designate the same or functionally identical or with respect to their functions corresponding elements. 1 shows a schematic representation of an optical system with an exemplary embodiment of the lens arrangement of the highly opened wide-angle lens;

Fig. 2 is a graphical representation of the field curvature of a

Weitwinkelob ektivs of Figure 1 with a focal length of 16 mm and a f-number of k = 2.8.

Fig. 3 is a graphical representation of the distortion of a

Wide-angle lens of Figure 1 with a focal length of 16 mm and a f-number of k = 2.8.

Fig. 4 is a graphical representation of the lateral chromatic aberration of a

5 is a graphical representation of the spherical aberration of a wide-angle lens according to FIG. 1 with a focal length of 16 mm and a f-number of k = 2, 8;

6 is a graphical representation of the spherical aberration of a wide-angle lens according to FIG. 1 with a focal length of 16 mm and a f-number of k = 2.2;

7 is a graphical representation of the spherical aberration of a wide-angle lens according to FIG. 1 with a focal length of 12 mm and a f-number of k = 2, 4. The technical data of three embodiments of the Weitwinkelob ektivs shown in Figure 1 are listed in Tables 1 to 6. 1 shows a list of the radii, the thicknesses or air spacings, the refractive indices and the Abbe numbers of a wide-angle lens according to FIG. 1 with a focal length of 16 mm and a f-number of k = 2.8;

a list of the aspheric coefficients of a wide-angle lens of Figure 1 with a focal length of 16 mm and a f-number of k = 2.8.

a list of the radii, the thicknesses, the refractive indices and the Abbe numbers of a wide-angle lens of Figure 1 with a focal length of 16 mm and a f-number of k = 2.2.

a list of the aspheric coefficients of a wide-angle lens of Figure 1 with a focal length of 16 mm and a f-number of k = 2.2.

a list of radii, thicknesses, refractive indices and Abbe numbers of a wide-angle lens of Figure 1 with a focal length of 12 mm and a f-number of k = 2.4.

a list of the aspheric coefficients of a wide-angle lens of Figure 1 with a focal length of 12 mm and a f-number of k = 2.4.

The embodiment whose lens arrangement is shown in Figure 1 schematically shows the basic structure of the proposed compact open-high-angle lens. All described embodiments have the same basic structure, but differ in terms of their focal length and the f-number. In the exemplary embodiment of the optical system 100 shown schematically in FIG. 1, the objective is a high-open wide-angle lens 102 with a focal length of 16 mm and a f-number of k = 2.8. In the illustration of FIG. 1, in each case the object side 104 is located on the left and the image page 106 with the digital acquisition sensor 108 on the right.

The wide-angle lens 102 shown in FIG. 1 consists, in the order in which it is viewed from the object side 104 to the image page 106 or to the image acquisition sensor 108, ie from left to right, of the following elements:

a) a first negative meniscus lens 112,

wherein the convex surface 110 of the meniscus lens 112 faces the object side 104;

b) a second positive lens 118,

wherein the more curved convex surface 116 of the lens 118 faces the object side 104

c) an aperture 122

d) a third positive lens 126, wherein the more curved convex surface 128 of the lens 126 faces away from the object side 104;

f) a fourth negative lens 130;

g) a fifth positive meniscus lens 136, wherein the convex surface 138 of the meniscus lens 136 faces the object side 104.

The third lens 126 and the fourth lens 130 are cemented together and form a doublet.

On the image side, a glass path 142 is included behind the last lens 136 of the wide-angle lens 102. As a rule, infrared cut filters and / or optical low-pass filters as well as a sensor coverglass are used. The total thickness is depending on the manufacturer between 0, 6 mm and 3 mm. As exemplary embodiments according to the basic structure of FIG. 1, three wide-angle lenses 102 are listed with the following optical characteristics:

Embodiment 1

Focal length 16 mm

F-number k = 2, 8

Embodiment 2:

Focal length 16 mm

F-number k = 2,2

Embodiment 3

Focal length 12 mm

F-number k = 2,4

The exact details of the individual surfaces of the optical elements of the three embodiments can be found in Tab. 1 to Tab. 3 together with the respective associated reference numerals.

In Tables 1, 2 and 3 are the lists of radii, the thicknesses or air distances, the refractive indices and the Abbe numbers of the three embodiments.

Tab. 1A, 2A and 3A list the aspherical data of the aspherical lens surfaces of the three wide-angle lenses presented as embodiments.

The surface of an aspherical lens can be generally described by the following formula:

z = + a _x r ² + a ₂ r ⁴ + a ₃ r ⁶ + a ₄ r ⁸ + a ₅ r ¹⁰ + a ₆ r ¹² + K

in which z is the arrow height (in mm) in the direction of the optical axis.

c indicates the so-called vertex curvature. It is used to describe the curvature of a convex or concave lens surface and is calculated from the reciprocal of the

Radius.

r indicates the distance from the optical axis (in mm) and r is a radial coordinate.

k indicates the so-called cone constant.

- a ± _r a2 _r 3 _r 3-4, 5, and ae represents the so-called Asphärenkoeffizien ^¬ th, which are the coefficients of a polynomial expansion of the function describing the surface of the asphere.

When focusing, it is advantageous if, in addition to the displacement of the lens as a whole in addition a floating focusing is performed. With floating focusing, the first air space behind the aperture is reduced. With the floating focusing for the next close focusing (ß '= - 0, l, distance to the object = 170 mm), the following values result:

Reference air distance explanation

to the next

Element / mm

104 170, 000 The distance between object 104 and first lens surface 114 is at least 170 mm.

122 4, 86 The air gap behind the panel is reduced by 0.3 mm. That is, the rear three lenses are shifted together toward the front two lenses. For If the object is located between infinity and 170 mm, the intermediate air distance behind the diaphragm is between 4.86 and 5.16 mm (see Table 1).

138 21, 54 The image-side intercept of the

Lens extends to

1.54 mm (see Table 1).

In FIGS. 2 to 7, some characteristic characteristics of the three exemplary wide-angle lenses 102 according to the basic structure according to FIG. 1 are shown graphically.

FIG. 2 shows graphically the field curvature 200 of a wide-angle lens 102 according to FIG. 1 with a focal length of 16 mm and a f-number of k = 2.8. Curve 202 shows the course of the tangential image shell, while curve 204 shows the course of the sagittal image shell. The horizontal axis (x-axis) indicates the longitudinal defocusing along the optical axis. The vertical axis (y-axis) contains the field coordinate from 0 ° field angle to the maximum field angle.

A graphical representation of the distortion 300 of a wide-angle lens 102 according to FIG. 1 with a focal length of 16 mm and a f-number of k = 2, 8 is shown in FIG. The horizontal axis (x-axis) indicates the percentage distortion in the range of -5% to +5%, while the values of the vertical axis (y-axis) correspond to the field coordinates from 0 ° field angle to the maximum field angle. The curve 302 represents the course of the distortion over the field angle up to maximum field angle. The distortion is always less than 3%.

FIG. 4 graphically shows the transverse chromatic aberration of a wide-angle lens 102 according to FIG. 1 with the focal length of 16 mm and a f-number of k = 2, 8. The horizontal axis (X axis) indicates the deviation of the centroid beam from the reference heavy beam at λ = 546.074 nm in microns. The vertical axis (y-axis) indicates the field coordinate from 0 ° field angle to the maximum field angle. The curve 402 shows the course of the deviation of the heavy beam from the reference heavy beam for λ = 643, 8469 nm over the field coordinate, while the curve 404 shows the course of the deviation of the heavy beam from the reference heavy beam for λ = 486.1327 nm over the field coordinates.

The graphical representation of the spherical aberration 500 of a wide-angle lens 102 with a focal length of 16 mm and a f-number of k = 2, 8 is shown in FIG. 5, while FIG. 6 is a graphical representation of the spherical one

Aberration 600 of a Weitwinkelob ektivs 102 with a focal ^¬ wide of 16 mm and an F-number of k = 2.2 and in Fig. 7, the spherical aberration 700 of a wide-angle lens 102 with a focal length of 12 mm and an F-number of k = 2, 4 is shown. The horizontal axis (x-axis) of

Diagrams indicate the longitudinal defocus along the optical axis and the vertical axis (y-axis) the radius of the entrance pupil of the objective. The diagrams show, respectively, the longitudinal deviation of an axial Aper- turstrahls for different heights of incidence in the Eintrittspu ^¬ pill, the trajectories 502, 602, 702 respectively for the wavelength λ = 546.074 nm (primary color) were calculated. There are other than the already mentioned focal lengths or aperture numbers all associated dimensions, eg. As radii and air distances, basically scalable. This makes it possible to realize not only the three examples described, but also a whole series of ob ects of the same kind but with different focal lengths. The wide angle lens can therefore be used for different applications.

reference numeral

100 optical system

102 wide-angle lens

104 object page

106 image page

108 image sensor

110 first surface of the lens 112

112 first lens

114 second surface of the lens 112th

116 first surface of the lens 118

118 second lens

120 second surface of the lens 118

122 aperture

124 first surface of the lens 126th

126 third lens

128 second surface of the lens 126 / first surface of the

Lens 130

130 fourth lens

132 second surface of the lens 130th

134 first surface of the lens 136th

136 fifth lens

138 second surface of the lens 136th

140 first surface of the transparent plate 142

142 transparent plate

144 second surface of the transparent plate 142nd

200 graphical representation of the field curvature of a wide-angle lens (focal length 16 mm, f-number k = 2.8)

202 Curve course of the tangential image shell

204 Curve of the sagittal image shell

300 graphical representation of the distortion of a wide-angle lens (focal length 16 mm, f-number k = 2.8) 302 Curve course of the distortion over the field angle

400 graphical representation of the lateral chromatic aberration of a ^wide-¬ winkelob ektivs (focal length 16 mm; f-number k = 2.8) 402 curve (for the lateral chromatic aberration deviation of the

Heavy beam from the reference heavy beam for

λ = 643.8469 nm over the field coordinate)

404 Curve for the lateral chromatic aberration (deviation of the

Heavy jet to the reference heavy beam for

λ = 486.1327 nm over the field coordinate)

500 graphical representation of the spherical aberration of a

Wide - angle lenses (focal length 16 mm, f - number k =

2, 8)

502 Curve of the longitudinal deviation of an axial aperture beam for different incidence heights in the entrance pupil

600 graphical representation of the spherical aberration of a

Wide-angle lens (focal length 16 mm, f-number k = 2.2)

602 Curve of the longitudinal deviation of an axial aperture beam for different incidence heights in the entrance pupil

700 graphical representation of the spherical aberration of a

Wide-angle lens (focal length 12 mm, f-number k = 2.4)

702 Curve of the longitudinal deviation of an axial aperture ray for different incidence heights in the entrance pupil quoted literature

US 7,239,457 B2

US 5, 631, 780

US 2009/0009887 AI

US 2003/0174410 Al

Tab. 1

Focal length 16 mm / aperture k

aspheric surface Tab. 1A

Tab. 1A (continued)

Tab. 2

Focal length 16 mm / aperture k

aspheric surface

Tab. 2A

Tab. 2A (continued)

Tab. 3

Focal length 12 mm / aperture k = 2,4

aspheric surface Tab. 3A

Tab. 3A (cont'd)

Claims

claims

1. Weitwinkelob ektiv (102) for digital image recording, which in the order given, as viewed from the object side (104), comprising the following elements:

a) a first negative meniscus lens (112),

wherein the convex surface (110) of the meniscus lens (112) faces the object side (104);

b) a second positive lens (118),

wherein the more curved convex surface (116) of the lens (118) faces the object side (104)

c) an aperture (122);

d) a third positive lens (126),

wherein the more curved convex surface (128) of the lens (126) faces away from the object side (104);

e) a fourth negative lens (130);

f) wherein the third positive lens (126) and the fourth negative lens (130) are cemented together; and

g) a fifth positive meniscus lens (136), the convex surface (138) of the meniscus lens (136) facing away from the object side (104);

h) wherein the wide-angle lens (102) has no further lenses;

i) the object facing surface (116) of the second lens (118) having an aspheric surface;

1) wherein the focal length of the first lens a value in the region of the loading ^¬ -1,0fachen to -1.2 times the overall focal length of Weitwinkelob ektivs (102).

2. Weitwinkelob ective (102) according to claim 1,

characterized,

in that the second positive lens (118) and / or the third positive lens (126) and / or the fourth negative lens (130) is a meniscus lens.

3. Wide-angle lens (102) according to one of the preceding claims,

which is designed in such a way

that focusing can be effected by shifting the entire objective (102) along the optical axis; and or

that focusing can be effected by changing the distance between the diaphragm (122) and the third positive lens (126).

4. Wide-angle lens (102) according to one of the preceding claims, characterized,

that the air gap on the image side behind the first lens is at least 0, 6 times the total focal length of the Weitwinkelob ektivs (102); and

in that the cutting distance behind the last lens surface (138) in the image-side direction is at least 1.25 times the total focal length of the wide-angle lens (102).

5. wide-angle lens (102) according to any one of the preceding claims,

characterized,

that the fourth lens is a negative meniscus lens, the concave surface of the lens facing the object side.

6. Wide-angle lens (102) according to one of the preceding claims,

characterized,

the first lens (112) has two aspherical surfaces.

A wide-angle lens (102) according to any one of the preceding claims,

characterized,

the fifth lens has two aspherical surfaces.

8. Wide-angle lens (102) according to one of the preceding claims,

characterized,

in that the image-side surface of the second lens has an aspherical surface.

9. Weitwinkelob ective (102) according to any one of the preceding claims,

characterized,

that the e ect-side surface of the third lens has an aspherical surface.

10. Weitwinkelob ective (102) according to any one of the preceding claims,

characterized,

in that the ratio of the Abbe numbers of the third lens to the Abbe number of the fourth lens is a value greater than or equal to 1.5.