Optical system for a side-viewing endoscope, and side-viewing endoscope

Abstract

An optical system having a viewing angle θ relative to a longitudinal axis including: a prism group to deflect incident light by reflection at first and second surfaces including prisms with mutually adjacent boundary surfaces arranged in pairs and separated by a gap, a total reflection of incident light from outside a field of view takes place at a boundary surface between a prism and a corresponding gap, the prism group has a cylindrical envelope (D), and an input-side prism is configured to have a wedge-shape with angle β and an optical path length α; an entry surface of the prism has a length L, which is a length of a line of intersection of the entry surface with a plane that is spanned by a central beam path; and the first prism meets the conditions: α<cos θ.Math.tan β.Math.D/2 and L<D/cos θ.

Claims

1. An optical system for a side-viewing endoscope with a central beam path that has a distal lateral viewing angle θ relative to a longitudinal axis of an endoscope shaft of the endoscope, the optical system comprising: a distal optical assembly having a prism group configured to deflect incident light from a field of view defined around the lateral viewing angle in a direction of the longitudinal axis of the endoscope shaft by means of reflection at a first reflective surface and at a second reflective surface; wherein the prism group comprises two or more prisms, mutually adjacent boundary surfaces of the two or more prisms are arranged in pairs parallel to each other and are separated by a gap in each case, wherein a total reflection of incident light from outside a field of view takes place at a boundary surface between a prism of the two or more prisms and a corresponding gap, wherein the prism group, in a cross section taken perpendicular to the longitudinal axis, has a shape of a circular segment within a cylindrical envelope with a diameter D, and an input-side first prism of the prism group is configured to have a wedge-shape with a wedge angle β and an optical path length α of the central beam path; an entry surface of the first prism has a length L, defined as a length of a line of intersection of the entry surface with a plane that is spanned by the central beam path; and the first prism meets the conditions:
α<cos θ.Math.tan β.Math.D/2 and L<D/cos θ.

2. The optical system according to claim 1, wherein the prism group comprises the first prism, a second prism and a third prism, wherein the second prism is configured to have a wedge-shape, wherein a wedge angle of the second prism borders a side of the first prism opposite the wedge angle of the first prism, and the wedge angle of the first prism borders a side of the second prism opposite the wedge angle of the second prism so that the gaps between the first, second and third prisms are angled relative to the central beam path in different directions.

3. The optical system according to claim 2, wherein the wedge angle of the second prism is 2.Math.β.

4. The optical system according to claim 1, wherein the gap is filled with a medium that has a lesser optical density than a glass used for the two or more prisms.

5. The optical system according to claim 4, wherein the medium is selected from a group consisting of a vacuum, an inert atmosphere or air.

6. The optical system according to claim 1, wherein the two or more prisms comprise at least the first prism and a second prism, at least one of the first prism and the second prism having one or more of a lower cut and an upper cut.

7. The optical system according to claim 6, wherein the lower cuts or upper cuts are formed stacked in height.

8. The optical system according to claim 1, further comprising a proximal optical assembly and at least one of an image sensor or an eyepiece disposed proximally to the proximal optical assembly.

9. The optical system according to claim 1, wherein the distal optical assembly comprises an entry lens arranged before the entry surface of the first prism in a direction of incident light.

10. A side-viewing endoscope comprising an optical system according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The embodiments are described below, without restricting the general idea of the invention, based on exemplary embodiments in reference to the drawings, whereby we expressly refer to the drawings with regard to the disclosure of all details that are not explained in greater detail in the text. In the following:

(2) FIG. 1 illustrates an optical system according to the prior art, in a schematically simplified longitudinal section,

(3) FIG. 2 illustrates an optical system in a schematically simplified longitudinal section,

(4) FIG. 3 illustrates an optical system of a stereo videoendoscope,

(5) FIGS. 4a and 4b illustrate a prism group with two prisms according to the prior art, as well as details of the first prism of the prism group,

(6) FIG. 5 illustrates an exemplary embodiment of a prism group with two prisms,

(7) FIG. 6 illustrates an exemplary embodiment of a prism group with three prisms,

(8) FIG. 7 illustrates a perspective view of the first prism of the prism group from FIG. 6, and

(9) FIGS. 8a and 8b illustrate details of an exemplary embodiment of a prism group with three prisms.

(10) In the drawings, the same or similar elements and/or parts are always provided with the same reference numbers; a reintroduction will therefore always be omitted.

DETAILED DESCRIPTION

(11) FIG. 2 shows an optical system 2 with a direct view according to the German patent application DE 10 2016 214 025.6 by the applicant, also in a simplified and schematic longitudinal section view along a vertical sectional plane. The optical system 2 comprises a distal optical assembly 10 and a proximal optical assembly 12. The distal optical assembly 10 and the proximal optical assembly 12 define a beam path 14 in the optical system 2. Light bundles 6 (of which only one is shown as an example) from the object space 4 entering the optical system 2 from within the field of view 20 are mapped on a light-sensitive surface 19 of the image sensor 18.

(12) The optical system 2 according to the depicted exemplary embodiment comprises a prism group 24 arranged in the beam path 14. The prism group 24 comprises at least one prism 30, 32, 34 and limits the field of view 20 of the optical system 2 on at least one side. Along with the prism group 24, the distal optical assembly 10 also comprises an entry lens 26 and an exit lens 28. The at least one prism 30, 32, 34 of the prism group 24 comprises a boundary surface 36, 38 on which the incident light beams 6″ entering the optical system 2 from outside the field of view 20 are reflected out of the beam path 14 with total reflection.

(13) The prism group 24 shown in FIG. 2 comprises, for example, a first prism 30, a second prism 32 and a third prism 34. The first prism 30 provides a first boundary surface 36 at which a first light bundle 40 (indicated by an arrow) is reflected out of the beam path 14. The second prism 32 provides a second boundary surface 38 at which a second light bundle 42 (also indicated by an arrow) is reflected out of the beam path 14 in another direction.

(14) The light bundles reflected out of the beam path 14 enter the optical system 2 as light bundles 6″ and 6′″ from outside the field of view 20. In FIG. 2, the incident light bundle 6′″ on the underside of the optical system 2 from outside the field of view 20 is completely reflected as a first light bundle 40 on the first boundary surface 36 and thus removed from the beam path 14. The incident light bundle 6″ entering the upper side of the optical system 2 from outside the field of view 20 is completely reflected as a second light bundle 42 on the second boundary surface 38 and thus reflected out of the beam path 14.

(15) The prism group 24 limits the field of view 20 on two mutually opposing sides, for example on a lower and an upper horizontal edge of the field of view 20. Incident light beams 6″, 6′″ entering the optical system 2, which enter from outside the field of view 20, are reflected out of the beam path 14 on these sides of the field of view 20. In the same way, by rotating the prism group 24 about the optical axis 16, a limitation, for example on the vertical edges of the field of view 20, can result as on the left or right side of the field of view 20. For this, the prism group 24 would have to be rotated by 90° about the optical axis 16; furthermore, it would have to be adapted to the required horizontal viewing angle (which is possibly larger than the vertical viewing angle). Such an adaptation takes place, for example, by a suitable choice of the inclination of the boundary surfaces 36, 38 with respect to the optical axis 16.

(16) A further prism group not depicted in FIG. 2 can also be added. With such an exemplary embodiment, a first prism group 24 would be arranged like the prism group 24 shown in FIG. 2, and a second prism group would be arranged afterward in the direction of incident light, rotated by 90° about the optical axis 16. Thus, a limitation of the field of view 20 could be achieved on both the horizontal and vertical limits of the field of view 20.

(17) FIG. 3 shows another optical system 2 according to the German patent application DE 10 2016 214 025.6 by the applicant. The optical system 2 is, for example, the optical system 2 of a stereo video endoscope with a lateral view. The optical system 2 includes, as part of the deflecting prism group 58, a prism group 24, which includes a boundary surface 36 on which the incident light bundle 6″ from outside the field of view 20 is reflected out of the beam path 14 as a first light bundle 40. The prism group 24 includes the first prism 30 and the second prism 32 for this purpose. Once again, a first air gap can be provided between the first boundary surface 36 of the first prism 30 so that total reflection takes place on the boundary surface 36. The first and second prisms 30, 32 can be configured in such a way that these replace the first deflecting prism 62 of the deflecting prism group 58; i.e. produce an equivalent optical effect (aside from the total reflection of light bundles 6″ not coming from the field of view 20). The prism group 24, which in each case is a part of the distal optical assembly 10, removes undesirable scattered light directly at the beginning of the optical system 2. This increases the imaging quality of the optical system 2.

(18) The prism group from FIG. 3 is structurally complex and large to build since it does not fit in a cylindrical envelope.

(19) FIG. 5 shows a first exemplary embodiment of a prism group 61 of an optical system 60. This is a prism group 61 with two prisms, i.e., a first prism 62 and a second prism 63, that are separated from each other by a gap 64. Also shown in FIG. 5 are the path α of the central beam path 67 through the first prism 62, the wedge angle β of the first prism 62, as well as the lateral viewing angle θ. Starting at the entrance, the central beam path 67 runs through the first prism 62, the gap 64, the second prism 63, and undergoes a reflection at the first reflective surface 65, as well as another reflection at the second reflective surface 66 where the central beam path 67 enters the central longitudinal axis 68 of the endoscope. The passage through the gap 64 ensures that light beams which enter at a larger angle from further up in FIG. 5 are reflected away by total reflection and are omitted from the beam path.

(20) FIG. 6 shows a second exemplary embodiment of a prism group 71 of an optical system 70. This prism group 71 has three prisms 72, 73 and 74 which are separated from each other by two gaps 75, 76. Also discernible are the path α of the central beam path 79 through the first prism 72, the wedge angle β of the first prism 72, and the lateral viewing angle θ of the optical system 70 which is 30° in this exemplary embodiment. Just as in the previous example, the central beam path 79 is reflected twice at a first reflective surface 77 and a second reflective surface 78 from the lateral entry direction into the direction of the endoscope shaft parallel with the axis of symmetry. It is discernible that for example the first prism 72 has a top cut 81. The other prisms 73, 74 are also cut at their top sides, or respectively bottom sides. In comparison to the known prism system according to, for example, FIGS. 4a and 4b, it is notable that there is significantly less dead glass volume toward the bottom.

(21) To a certain extent, FIG. 6 shows that the two gaps 75, 76 are arranged mirrored to each other relative to the first section of the central beam path 79 so that they cause a symmetrical expulsion by total reflection of light beams that enter from further up or further below outside of the visual field into the prism group 71.

(22) FIG. 7 shows a perspective view of the first prism 72 of the prism group 71 from FIG. 6 in which it is discernible that this prism 72 is fitted into a cylindrical envelope 85. The top cut 81 of the first prism 72 is also discernible as a transparent region 82 that is provided for the desired beam path as well as an opaquely coated edge 83 which can be coated with an anti-flare coating 84.

(23) FIG. 8a shows a cross-sectional view of the embodiment according to FIG. 6 in greater detail. The plane of the cross-sectional view corresponds to the plane of symmetry 90 of the optical system 70 that is shown in FIG. 8b.

(24) In addition to the angles β and θ which are defined as above and the length α of the section of the central beam path 79 which runs through the first prism 72, the length L of the entry surface of the first prism 72 as well as the diameter D of the envelope 85 of the prism group 71 of the optical system 70 are shown in FIG. 8a. The length L of the entry surface of the first prism 72 is the length of the entry surface in the plane of symmetry 90 of the prism group in which the entire central beam path 79 also runs. The diameter D of the envelope is the same as the diameter of the circular projection of the envelope which is shown in FIG. 8b. FIG. 8b also shows the sequence of the upper cuts 81, 81′, 81″ of the three prisms 72, 73 and 74 which form a sequence of steps that are also discernible in FIG. 8a. These form stop edges 86, 87 on the top side of the prism group 71. FIGS. 8a and 8b also show the anti-flare coating 84 of the prism group 71 as well as the lower cuts 88, 88′, 88″ of the prisms 72, 73 and 74.

(25) In FIG. 8a, it is also discernible that, after the second reflection, the central beam path 79 coincides with the central longitudinal axis 80 of the endoscope shaft. It is also discernible that the material of the prism group 71 in the bottom region does not completely fill the envelope 85; instead, a bottom empty space remains. In a completely assembled state, this is filled on the one hand by a corresponding holder which can also have space for light-conducting means such as light-conducting fibers.

(26) The geometry of the prism 73 meets the conditions:
α<cos θ.Math.tan β.Math.D/2 as well as
L<D/cos θ.

(27) Given these conditions, it is reliably possible to find compact prism groups that can be fitted in a cylindrical envelope having minimal optical dead volume with a lateral view and simultaneously total reflection of laterally entering light beams at the gap or gaps of the prism group, and that accordingly require minimal installation space.

(28) With the given lateral viewing angle θ, it is for example accordingly possible to adjust the angle at which light beams entering from outside of the planned field of view can be removed by total reflection using the wedge angle β of the first prism 72 and possibly the corresponding wedge angle of the second prism 73. The path length α can then be adjusted by shifting the first prism 72 at the boundary surface relative to the second prism 73. The diameter D can be specified corresponding to the available installation space, whereas the length L of the entrance surface of the first prism 72 then results from the combination of the selected parameters and the cuts to be selected relative to the cylindrical envelope.

(29) While there has been shown and described what is considered to be preferred embodiments, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.

LIST OF REFERENCE SIGNS

(30) 2 Optical system

(31) 4 Object space

(32) 6, 6′, 6″, 6′″ Light bundles

(33) 8 Entry window

(34) 10 Distal optical assembly

(35) 12 Proximal optical assembly

(36) 14 Beam path

(37) 16 Optical axis

(38) 18 Image sensor

(39) 19 Light-sensitive surface

(40) 20 Field of view

(41) 22 Scattering center

(42) 24 Prism group

(43) 26 Entry lens

(44) 28 Exit lens

(45) 30 First prism

(46) 32 Second prism

(47) 34 Third prism

(48) 36 First boundary surface

(49) 38 Second boundary surface

(50) 40 First light bundle

(51) 42 Second light bundle

(52) 58 Deflecting prism group

(53) 60 Optical system

(54) 61 Prism group

(55) 62 First prism

(56) 63 Second prism

(57) 64 Gap

(58) 65 First reflective surface

(59) 66 Second reflective surface

(60) 67 Central beam path

(61) 68 Longitudinal axis of the endoscope shaft

(62) 70 Optical system

(63) 71 Prism group

(64) 72 First prism

(65) 73 Second prism

(66) 74 Third prism

(67) 75 First gap

(68) 76 Second gap

(69) 77 First reflective surface

(70) 78 Second reflective surface

(71) 79 Central beam path

(72) 80 Longitudinal axis of the endoscope shaft

(73) 81, 81′, 81″Upper cut

(74) 82 Transparent region

(75) 83 Opaquely coated edge

(76) 84 Anti-flare coating

(77) 85 Cylindrical envelope

(78) 86, 87 Stop edge

(79) 88, 88′, 88″Lower cut

(80) 89 Bottom empty space

(81) 90 Plane of symmetry

(82) 100 Distal optical assembly

(83) 102 First prism

(84) 104 Second prism

(85) 106 Gap

(86) 108 First reflective surface

(87) 110 Second reflective surface

(88) 112 Central beam path

(89) 114 Optically unused glass volume