Optical system of a stereo video endoscope with a side-view direction and method for producing the same

Description

[0001] The invention relates to an optical system of a stereo video endoscope with a lateral viewing direction, comprising a sideways-viewing distal optical assembly and a proximal optical assembly, wherein the proximal optical assembly comprises a left lens system channel and a right lens system channel, which are constructed in the same way, and wherein the distal optical assembly is configured to couple incident light from an object space into the left lens system channel and the right lens system channel of the proximal optical assembly, and wherein the distal optical assembly comprises, in a light incidence direction, an entrance lens, a deflection prism group, and an exit lens, wherein the deflection prism group comprises, in a light incidence direction, a first prism and a second prism, wherein the first prism comprises a first entrance side and a first exit side inclined relative to the first entrance side,and wherein the second prism comprises a second entrance side, a reflection side and a second exit side.,

[0002] Furthermore, the invention relates to a stereo video endoscope with a lateral viewing direction and to a method for producing an optical system of a stereo video endoscope with a lateral viewing direction, wherein the stereo video endoscope comprises a sideways-viewing distal optical assembly and a proximal optical assembly, and wherein the proximal optical assembly comprises a left lens system channel and a right lens system channel that are constructed in the same way, and wherein the distal optical assembly is configured to couple light incident from an object space into the left lens system channel and the right lens system channel of the proximal optical assembly, and wherein the distal optical assembly comprises, in a light incidence direction, an entrance lens, a deflection prism group, and an exit lens, wherein the deflection prism group comprises, in a light incidence direction, a first prism and a second prism,wherein the first prism comprises a first entrance side and a first exit side inclined relative thereto, and wherein the second prism comprises a second entrance side, a reflection side and a second exit side.,

[0003] Video endoscopes, in which the light entering the distal tip of an endoscope shaft is directed by an optical system onto one or more image sensors, are available in various designs. There are endoscopes with a straight-ahead view, a so-called 0° viewing direction, endoscopes with a (fixed) lateral viewing direction, and endoscopes with an adjustable viewing direction (also known as V-DOV endoscopes).

[0004] Stereo video endoscopes are also known, which are designed to record a stereoscopic image pair and / or two stereoscopic video channels. Such instruments make it possible to create a 3D image of an object located distal to the end of the endoscope shaft in an examination or operating room.

[0005] Stereo video endoscopes with a lateral viewing direction are endoscopes that view sideways and have a fixed viewing angle that deviates from the straight-ahead view. Such endoscopes often comprise a prism arrangement consisting of several prisms that reflect the light rays entering the optical system from the object space at an angle to the longitudinal axis of the endoscope shaft twice and redirect them in the correct direction toward the endoscope shaft. Such an endoscope is known, for example, from DE 10 2014 206 513 A1 by the applicant Olympus Winter & Ibe, Hamburg.

[0006] A deflecting prism arrangement of such a stereo video endoscope typically comprises two or three prisms. The prisms are often cemented together at their common interfaces. In such a deflecting prism arrangement, the reflection of the incoming light beams takes place at two reflective interfaces of a second prism, which are inclined both to the optical axis of the entrance lens and to the longitudinal axis of the endoscope shaft. The second prism of the deflecting prism arrangement is located in the direction of light incidence behind a first prism, which is arranged directly behind the entrance lens. The inclined reflective interface of the second prism, at which the second reflection takes place, partially forms a common interface with the first prism, which the incoming light rays first pass through.

[0007] The entrance lens of the optical system of such a stereo video endoscope defines the optical axis of the optical system. The optical system includes apertures or menisci that define the field of view or the aperture angle of the optics. Light beams entering the optical system within the field of view are imaged by the optical system onto one or more image sensors. Light beams entering the optical system from outside the field of view often lead to reflections within the optical system, thus creating so-called "ghost images" or "flares."

[0008] A known deflection prism group in which such ghost images can arise comprises a first prism and a second prism that are cemented together. The first prism has an entrance side and an exit side, with the entrance side being inclined relative to the exit side. The exit side of the first prism is directly adjacent to a second entrance side of the second prism. For example, the first and second prisms are cemented together on these two sides. The second prism further comprises a reflection side and a second exit side. Light that enters the deflection prism group from the image field passes through the entrance side of the first prism and exits again at its exit side. The light then passes directly through the second entrance side into the second prism, is reflected at the reflection side within the second prism, and exits it at the exit side.

[0009] A peripheral light ray entering the optics at a large angle to the optical axis of the entrance lens passes through the entrance lens into the first prism and traverses its entrance and exit sides. At the same time as passing through the first exit side, the light ray also traverses the second entrance side of the second prism. As already mentioned, these two prism surfaces can be cemented together. The light ray is then reflected off the reflection side of the second prism and strikes the common interface between the first and second prisms at an acute angle, i.e., from the back side, the second entrance side of the second prism. There, the light ray undergoes Fresnel reflection or total internal reflection and is reflected back to the reflection side of the second prism.From there, it returns to the second entrance side of the second prism and is again reflected from the inside at this interface, for example, by total internal reflection. The light beam then enters a left or right lens system channel, where it creates a ghost image. This familiar quadruple reflection in the deflection prism group is undesirable.

[0010] DE 10 2013 215 422 A1 discloses an optical system for a stereo video endoscope with a lateral viewing direction, which has a raised negative meniscus as the entrance lens. The optical system comprises a deflection prism arrangement with boundary surfaces at which the light beams guided in the beam path are reflected. For this purpose, the boundary surfaces are mirrored.

[0011] EP 2 730 210 A1 shows an endoscope with a high-resolution image sensor. This endoscope comprises a deflection prism unit in which incident light is first reflected at a first reflection surface and then at a second reflection surface. Total internal reflection is explicitly mentioned only in connection with reflection at the second interface.

[0012] US 5,861,987 A shows a stereo endoscope with a tubular, elongated insertion part in which an optical object system is arranged. In the distal section, an oblique-viewing prism is arranged, consisting of two partial prisms that redirect incoming light in the direction of the optical axis.

[0013] JP H09288240 A shows an optical system of an endoscope configured to change the viewing direction. The system comprises a prism and an optical element. Reflection at the sides of the prism redirects incident light toward the optical element. One of the side surfaces is partially coated with a metal coating.

[0014] The object of the invention is to provide an optical system of a stereo video endoscope with a fixed lateral viewing direction, a stereo video endoscope with a fixed lateral viewing direction and a method for producing and repairing an optical system of a stereo video endoscope with a fixed lateral viewing direction, which is less sensitive to light beams incident from outside the field of view, in particular with regard to ghost images.

[0015] The object is achieved by an optical system of a stereo video endoscope with a fixed lateral viewing direction, comprising a sideways-viewing distal optical assembly and a proximal optical assembly, wherein the proximal optical assembly comprises a left lens system channel and a right lens system channel, which are constructed in the same way, and wherein the distal optical assembly is configured to couple incident light from an object space into the left lens system channel and the right lens system channel of the proximal optical assembly, and wherein the distal optical assembly comprises, in a light incidence direction, an entrance lens, a deflection prism group, and an exit lens, wherein the deflection prism group comprises, in a light incidence direction, a first prism and a second prism, wherein the first prism comprises a first entrance side and a first exit side inclined relative to the first entrance side,and wherein the second prism comprises a second entrance side, a reflection side, and a second exit side, wherein the first entrance side and the reflection side enclose an angle that is greater than a total reflection angle of the second prism, wherein a first partial surface of the reflection side of the second prism is provided with a reflective layer and a second partial surface of the reflection side is optionally uncoated or provided with an anti-reflection coating, wherein the first and second partial surfaces complement each other to form the total surface of the reflection side, wherein the optical system is further developed in that a distance between the first entrance side and the reflection side in the first partial surface is always greater than a distance between the first entrance side and the reflection side in the second partial surface.

[0016] Light beams entering the optical system from an image field in object space pass through the first entrance side of the first prism, are deflected at the interface of the prism body, and reach the first exit side of the first prism. The first exit side of the first prism is, for example, cemented to the second entrance side of the second prism. The light beams pass through this interface to the second entrance side of the second prism. They are deflected at the interface of the prism body and reach the rear reflection side of the second prism. From there, the light beams are reflected back to the second entrance side of the second prism and, within the prism body of the second prism, experience total internal reflection at this interface. The light beams are therefore reflected on an inner side of the second entrance side.From there, the light beams leave the deflection prism group through the exit side of the second prism.

[0017] In the context of this description, the "angle of total reflection" refers to the critical angle of total internal reflection. This angle is determined by the material of the first and second prisms, more precisely by the refractive index of the materials used. In particular, the first prism and the second prism are made of identical material, for example, the same type of glass.

[0018] The calculation of the total reflection angle Θc is carried out, for example, using the formula Θ C = arcsin n 1 / n 2 , where n1 = 1 for air and n2>1 is the refractive index of the prism material.

[0019] This is the refractive index as used in Snell's law of refraction. It does not use the complex refractive index, which is expressed as a complex number to account for the absorption of the wave in the medium.

[0020] It is further provided, in particular, that the left lens system channel has a left optical axis and the right lens system channel has a right optical axis. The left optical axis and the right optical axis are, in particular, aligned parallel to one another.

[0021] In the context of this description, a "lateral viewing direction" or the term "sideways viewing" is understood as follows: The stereo video endoscope has a shaft.

[0022] This shaft is either rigid or flexible. A rigid shaft has a longitudinal extension. A flexible shaft has a longitudinal extension at its distal end. The endoscope's viewing direction forms an angle with this longitudinal extension that is different from zero. This angle is constant. For example, such an angle is 30°.

[0023] In the optical system according to aspects of the invention, quadruple reflection at the interfaces of the deflection prism group, as is known per se from the prior art, is advantageously excluded. In stereo video endoscopes, the reflection surface of the second prism must be larger than in prisms of endoscopes that do not provide stereoscopic imaging. This is necessary because the largest possible stereo base should be realized for the right and left stereo channels. A large stereo base allows the creation of a large 3D effect. However, this design requirement leads to the aforementioned risk of multiple reflections, in particular the described quadruple reflection. These reflections create unwanted ghost images. By arranging the first entrance side and the reflection side at the described angle, such (multiple) reflections are effectively suppressed.

[0024] According to an advantageous embodiment, the optical system is further developed in that the optical system is arranged such that light rays incident from a field of view of the optical system strike the reflection side of the second prism at an angle which is greater than the total reflection angle.

[0025] In this context, it is particularly provided that the optical system comprises at least one aperture which limits the field of view of the optical system, wherein the angle between the first entrance side and the reflection side is set taking into account a material of the second prism which defines a refractive index and thus a total reflection angle, and taking into account a maximum viewing angle which is defined by the field of view, such that total reflection takes place on the reflection side of the second prism for all light rays incident from the field of view.

[0026] By optimizing the ratios between the angle of incidence controlled by apertures or menisci on the first entrance side of the first prism, all light beams entering the optical system from the interior of the image field are totally reflected on the reflection side of the second prism.

[0027] The optical system is further developed in that a first partial surface of the reflection side of the second prism is provided with a reflective layer and a second partial surface of the reflection side is optionally uncoated or provided with an anti-reflective coating, wherein the first and the second partial surface complement each other to form the total surface of the reflection side.

[0028] An anti-reflective coating, for example, is a coating such as that used in the coating of photographic optics. Anti-reflective coatings are used there to reduce the reflectance of the optical surfaces of lenses, objectives, prisms, or plates and increase transmission. Lenses and eyepieces with such a coating are often referred to as a coating, while eyeglasses or viewing windows are often referred to as an anti-reflective coating.

[0029] The reflective layer is applied in particular to an outer surface of the reflection side of the second prism. It is a reflective coating, for example a vapor-deposited layer of silver (Ag) or aluminum (Al). The reflective coating ensures that light rays are reflected on an inner surface, i.e. in the prism body. Light rays exit the reflection side of the second prism through the part of the reflection side with the non-reflective coating. These are the light beams that enter the optical system at large angles from outside the image field and lead to the typical quadruple reflections in conventional optical systems. In the optical system according to aspects of the invention, the formation of ghost images is advantageously prevented or suppressed.

[0030] It is further provided that the distance between the first entrance side and the reflection side in the first partial surface is always greater than the distance between the first entrance side and the reflection side in the second partial surface. The non-reflective coated second partial surface of the reflection side is thus located in a lower, narrow region of the second prism.

[0031] Furthermore, the optical system is advantageously further developed in that first light rays incident from an object space are reflected in the first partial area of ​​the reflection surface and coupled into the left lens system channel and second light rays incident from the object space are reflected in the second partial area of ​​the reflection surface and coupled into the right lens system channel.

[0032] For example, the optical axis of the entrance lens defines the position of a dividing line between the partial surfaces. This dividing line can also be located 50%, 40%, 30%, or 20% from the bottom edge, each with reference to the total height of the surface in this direction.

[0033] The object is further achieved by a stereo video endoscope with a fixed lateral viewing direction, which is further developed in that it comprises an optical system according to one or more of the aforementioned embodiments.

[0034] The stereo video endoscope offers the same or similar advantages as those already mentioned with regard to the optical system itself. The advantage of such a stereo video endoscope is that ghost images do not occur, even with light beams entering its optical system at large angles.

[0035] The object is further achieved by a method for producing an optical system of a stereo video endoscope with a fixed lateral viewing direction, wherein the stereo video endoscope comprises a sideways-viewing distal optical assembly and a proximal optical assembly, and wherein the proximal optical assembly comprises a left lens system channel and a right lens system channel, which are constructed in the same way, and wherein the distal optical assembly is configured to couple light incident from an object space into the left lens system channel and into the right lens system channel of the proximal optical assembly, and wherein the distal optical assembly comprises, in a light incidence direction, an entrance lens, a deflection prism group, and an exit lens, wherein the deflection prism group comprises, in a light incidence direction, a first prism and a second prism,wherein the first prism comprises a first entrance side and a first exit side inclined relative thereto, and wherein the second prism comprises a second entrance side, a reflection side, and a second exit side, wherein the first and second prisms are selected or arranged such that the first entrance side and the reflection side enclose an angle that is greater than a total reflection angle of the second prism, wherein a first partial surface of the reflection side of the second prism is provided with a reflective layer and a second partial surface of the reflection side is optionally left uncoated or is provided with an anti-reflective coating, wherein the first and second partial surfaces complement each other to form the total surface of the reflection side, wherein this method is further developed in thatthat a distance between the first entrance side and the reflection side in the first partial area is always greater than a distance between the first entrance side and the reflection side in the second partial area.,

[0036] The selection is made such that the optical system is configured so that light rays incident from an image field of the optical system strike the reflection side of the second prism at an angle greater than the angle of total reflection. Furthermore, the same or similar advantages apply to the method as already mentioned with regard to the optical system itself, so repetition is avoided.

[0037] The method is particularly developed in that the optical system is provided with at least one aperture which

[0038] Field of view of the optical system is limited, wherein the angle between the first entrance side and the reflection side is set taking into account a material of the second prism, which determines a refractive index and thus a total reflection angle, and taking into account a maximum viewing angle which is determined by the field of view, such that total reflection takes place for all light rays incident from the field of view on the reflection side of the second prism.

[0039] Finally, the object is achieved by a method for repairing a stereo video endoscope with a lateral viewing direction, wherein an optical system of the stereo video endoscope comprises a sideways-viewing distal optical assembly and a proximal optical assembly, and wherein the proximal optical assembly comprises a left lens system channel and a right lens system channel, which are constructed in the same way, and wherein the distal optical assembly is configured to couple incident light from an object space into the left lens system channel and the right lens system channel of the proximal optical assembly, and wherein the distal optical assembly comprises, in a light incidence direction, an entrance lens, a deflection prism group, and an exit lens, wherein the deflection prism group comprises, in a light incidence direction, a first prism and a second prism,wherein the first prism comprises a first entrance side and a first exit side inclined relative thereto, and wherein the second prism comprises a second entrance side, a reflection side, and a second exit side, wherein the deflection prism group is exchanged and replaced by a new deflection prism group in which the first and second prisms are selected or arranged such that the first entrance side and the reflection side enclose an angle that is greater than a total reflection angle of the second prism, wherein a first partial surface of the reflection side of the second prism is provided with a reflective layer and a second partial surface of the reflection side is optionally left uncoated or is provided with an anti-reflective coating, wherein the first and second partial surfaces complement each other to form the total surface of the reflection side, wherein this method is further developed in thatthat a distance between the first entrance side and the reflection side in the first partial area is always greater than a distance between the first entrance side and the reflection side in the second partial area.,

[0040] The method for repairing the stereo video endoscope advantageously creates the possibility of improving existing endoscopes with regard to their susceptibility to ghost images.

[0041] In the context of this description, a coating on the reflective side always refers to a reflective coating, for example, with silver (Ag) or aluminum (Al). Therefore, if the reflective side is uncoated or partially uncoated, the reflective side has no reflective coating or only partially has no reflective coating.

[0042] Further features of the invention will become apparent from the description of embodiments of the invention together with the claims and the accompanying drawings. Embodiments of the invention may fulfill individual features or a combination of several features.

[0043] The invention is described below, without limiting the general inventive concept, using exemplary embodiments with reference to the drawings, whereby express reference is made to the drawings for all details of the invention not explained in more detail in the text. They show: Fig. 1 shows a stereo video endoscope in a schematically simplified representation, Fig. 2 shows a schematically simplified representation of an optical system of a stereo video endoscope according to the prior art in a sectional view, Fig. 3 shows a schematically simplified representation of the optical system of a stereo video endoscope, wherein the beam path of the left lens system channel is shown, and Fig. 4 shows a schematically simplified representation of the optical system of a stereo video endoscope, wherein the beam path of the right lens system channel is shown.

[0044] In the drawings, identical or similar elements and / or parts are provided with the same reference numbers, so that a repeated presentation is omitted.

[0045] Fig. 1shows a schematically simplified perspective view of a stereo video endoscope 2, comprising a proximal handle 4, to which a rigid endoscope shaft 6 is connected. The endoscope shaft 6 can also be flexible or semi-flexible. At a distal tip 8 of the endoscope shaft 6 there is an entrance window 10, through which light from an object space 11, for example from an operating and / or observation field, is directed into a Fig. 1 enters the invisible optical system of the stereo video endoscope 2. The optical system of the stereo video endoscope 2 is arranged, for example, in a distal section 12 of the endoscope shaft 6. The optical system images objects located in the object space 11 onto image sensors. These image sensors are, for example, high-resolution ones, e.g., HD, 4K, or the following technologies.

[0046] The stereo video endoscope 2 shown is a surgical instrument. Furthermore, it is an endoscope with a fixed lateral viewing direction. The entrance window 10 is mounted at an angle in the endoscope shaft 6, so that an optical axis of the entrance lens of the optical system (not shown) forms a fixed angle with a longitudinal extension direction L of the endoscope shaft 6 of the stereo video endoscope 2. This angle is, for example, between 10° and 30°.

[0047] A change in the viewing direction around a longitudinal axis of the endoscope shaft 6 is effected by rotating the handle 4. The optical system located in the distal section 12 rotates with this rotation of the handle 4. To maintain the horizontal position of the displayed image, a rotary wheel 14 is held in place when the handle 4 is rotated. This prevents the image sensors inside the endoscope shaft 6 from following the rotational movement.

[0048] Fig. 2 shows an optical system 20 as used in stereo video endoscopes 2 according to the prior art.

[0049] The optical system 20 defines the fixed lateral viewing direction of the stereo video endoscope 2. The optical axis 22 forms a fixed angle of, for example, 30° with the longitudinal extension direction L of the endoscope shaft 6. The optical system 20 comprises a laterally viewing distal optical assembly 24 and a proximal optical assembly 26. Light entering from the object space 11 through the entrance window 10 first strikes the entrance lens 28 and then enters a deflecting prism group 30 of the distal optical assembly 24. The deflecting prism group 30 comprises, in succession in the direction of light incidence, a first prism 32 and a second prism 34.

[0050] In the direction of light incidence, the light beams leaving the entrance lens 28 first pass through a first entrance side 36 of the first prism 32. The light beams pass through the body of the first prism 32 and reach its first exit side 38. The first exit side 38 is inclined relative to the first entrance side 36. The first prism 32 and the second prism 34 are, for example, cemented together. The second prism 34 comprises a second entrance side 40 through which the light exiting the first prism 32 through its first exit side 38 enters the second prism 34. The first exit side 38 of the first prism 32 and the second entrance side 40 of the second prism 34 are cemented together in the example shown. The second prism 34 further comprises a reflection side 42 which is inclined relative to the second entrance side 40.The light beams entering the second prism 34 via the second entrance side 40 are reflected by the reflection side 42 of the second prism 34. From there, they impinge on the second entrance side 40 of the second prism 34 from the rear side. The entrance side 40 is coated with a reflective coating, for example, in an upper region where it does not border the exit side 38 of the first prism 32. Furthermore, as an alternative to cementing the first and second prisms 32, 34, a mask is arranged between the exit side 38 of the first prism 32 and the entrance side 40 of the second prism 34. This mask creates an air gap between the exit side 38 and the entrance side 40, so that the light rays reflected from the inside at the entrance side 40 are totally reflected at the glass-air interface.The light beams are reflected at the rear of the entrance side 40 at such an angle that they subsequently exit the second prism 34 at its second exit side 44. From there, the light beams continue in the direction of light incidence to an exit lens 46 of the distal optical assembly 24.

[0051] The proximal optical assembly 26 comprises a left lens system channel 48L and a right lens system channel 48R. The left and right lens system channels 48L, 48R are of similar or even identical construction. They are further arranged such that Fig. 2A left optical axis (not shown) and a right optical axis (also not shown) of the left and right lens system channels 48L, 48R are aligned parallel to one another. The left lens system channel 48L includes an imaging left lens group 50L that images the incident light onto a left image sensor 52L. Correspondingly, the right lens system channel 48R includes an imaging right lens group 50R that images the incident light onto a right image sensor 52R.

[0052] The distal optical assembly 24 is configured to couple the light beams incident from the object space 11 into both the left lens system channel 48L and the right lens system channel 48R.

[0053] In endoscopes known from the prior art, the reflection side 42 of the second prism 34 is provided with a reflective coating over its entire surface. For example, the outer surface of the second prism 34 is vapor-deposited with aluminum (Al) or silver (Ag) on ​​the reflection side 42.

[0054] The surface area of ​​the reflection side 42 of the second prism 34 is significantly larger in stereo video endoscopes than in endoscopes that do not provide stereoscopic images. This is necessary to allow the greatest possible separation between the left and right stereo channels. Such a large stereo base enables a strong 3D effect.

[0055] However, such a prism construction has the technical disadvantage that multiple reflections quickly occur, creating a so-called ghost image. Such ghost images are generated by peripheral light rays that enter the optical system 20 from the object space 11 at a large angle to the optical axis 22.

[0056] Such a peripheral light beam passes through the entrance lens 28 into the first prism 32 and from there into the second prism 34. It strikes the reflection side 42 of the second prism 34, is reflected there and strikes the interface between the first and second prisms 32, 34 at an acute angle. From there it is reflected back to the reflection side 42 of the second prism 34 and again reaches the second entrance side 38 of the second prism 34. Total reflection occurs again at this interface, so that the light beam then leaves the deflection prism group 30 via the exit side 44 and creates a ghost image in the left or right lens system channel 48L, 48R.

[0057] Fig. 3 shows an optical system 20 in a schematically simplified representation according to an embodiment. For the sake of simplicity, only the left lens system channel 48L is shown in the optical system.

[0058] Fig. 4 shows a corresponding representation of an optical system 20 according to an embodiment, wherein the right lens system channel 48R is shown in this representation.

[0059] Fig. 3 shows the ray path of light beams falling into the left lens system channel, correspondingly shows Fig. 4 the beam path of light beams falling into the right lens system channel 48R. The light rays imaged into the left lens system channel originate from a field of view of the left channel 54L, and the light rays imaged into the right lens system channel 48R originate from a field of view of the right channel 54R.

[0060] In Fig. 3, a light beam 56 is shown as an example, which enters the optical system 20 at a large angle to the optical axis 22. It enters an area of ​​the second prism 34, which shall also be referred to as the "B-down area." This B-down area 58 is typically not used by the light beams that are imaged into the left lens system channel 48L. The light rays that fall into the right lens system channel (cf. Fig. 4 ), however, are reflected in the B-down region 58 of the reflection side 42 of the second prism 34. Thus, it may happen that the light beam 56, which is reflected in the B-down region 58 of the second prism 34, enters the right lens system channel 48R and creates a ghost image there.

[0061] In order to suppress or completely eliminate this phenomenon, among other things, the optical system 20 is configured such that the first entrance side 36 of the first prism 32 and the reflection side 42 of the second prism 34 enclose an angle α which is greater than a total reflection angle θ C of the second prism 34.

[0062] The total reflection angle θ C is calculated using the well-known formula Θ C = arcsin n 1 / n 2 where n1 = 1 for air and n2>1 is the refractive index of the material of the second prism 34.

[0063] The first and second prisms 32, 34 are, in particular, made of the same or identical material. At least, materials with at least approximately the same refractive index are used for the two prisms 32, 34. For example, the two prisms 32, 34 are made of the same glass.

[0064] The refractive index of the material is the refractive index as used in Snell's law of refraction. It is not the complex refractive index.

[0065] The optical system 20 is configured such that the light rays incident into the optical system 20 from a field of view 54L, 54R strike the reflection side 42 of the second prism 34 at an angle that is greater than the angle of total reflection. Thus, it is possible for the second partial surface 64 of the reflection side 42 of the second

[0066] prism 34 can remain uncoated, i.e. it is not vapor-coated with a reflective layer such as Al or Ag. It is also provided that the second partial surface 64 of the reflection side 42 of the second

[0067] Prism 34 is provided with an anti-reflective coating, as is known, for example, from photographic optics.

[0068] It is further provided in particular that the optical system 20 comprises at least one aperture 60R, 60L, which limits the field of view 54L, 54R of the optical system 20. In the illustrated embodiment, separate apertures 60L, 60R are provided for the left and right lens system channels 48L, 48R, namely the left aperture 60L and the right aperture 60R.

[0069] The angle α between the first entrance side 36 of the first prism 32 and the reflection side 42 of the second prism 34 is set taking into account a material of the second prism 34, which determines a refractive index n2 and thus a total reflection angle θ C, and taking into account a maximum viewing angle which is determined by the field of view 54L, 54R, such that total reflection takes place at the reflection side 42 of the second prism 34 for all light rays incident from the field of view 54L, 54R.

[0070] Conversely, this means that light rays entering the optical system 20 from outside the field of view 54L, 54R, such as the light beam 56 that causes a ghost image in conventional systems, are not totally reflected at the second partial surface 64 of the reflection side 42 of the second prism 34. Such light rays leave the optical system 20, more precisely the second partial surface 64 of the reflection side 42 of the second prism 34, and are absorbed, for example, on a blackened inner side of a tube accommodating the optical system 20.

[0071] By optimizing the ratio between the angles of incidence controlled by the menisci and diaphragms 60R, 60L on the reflection side 42 of the second prism 34 for all rays incident from within the fields of view 54L, 54R, total internal reflection can be achieved on the reflection side 42. For example, an angle of incidence on the first entrance side 36 of the first prism 32 must be -7.6° (the minus sign used in the figures indicates a clockwise rotation), with the angle α being 36° and S-LAH 58 being used as the material for the prisms. In such a case, all light rays incident on the second partial surface 64 of the reflection side 42 are totally internally reflected. A coating of this surface can be omitted entirely, or the surface can be provided with an anti-reflection coating.

[0072] According to the claimed invention, it is provided that a first partial surface 62 of the reflection side 42 of the second prism 34 is provided with a reflective layer and a second partial surface 64 of the reflection side 42 is uncoated or is provided with an anti-reflective coating. The first and second partial surfaces 62, 64 are shown, for example, in Fig. 4 shown. Furthermore, the second partial surface 64 corresponds, for example, to the B-down region 58. According to the invention, the first and second partial surfaces 62, 64 complement each other to form the total surface of the reflection side 42. This advantageously creates the possibility for light rays 56, which cause ghost images in conventional systems, to leave the reflection side 42 of the second prism 34 in the B-down region 58.

[0073] According to the invention, the first and second partial surfaces 62, 64 are further arranged on the reflection side 42 of the second prism 34 such that a distance between the first entrance side 36 of the first prism 32 and the reflection side 42 of the second prism 34 in the first partial surface 62 is always greater than a corresponding distance between the first entrance side 36 and the reflection side 42 in the second partial surface 64. In other words, the second partial surface 64 is consistently closer to the first entrance side 36 than the first partial surface 62.

[0074] It is further provided in particular that the first and second partial surfaces 62, 64, unlike in Fig. 4shown, overlap. In such an embodiment, it is further provided, for example, that first light rays incident from an object space 11 are reflected in the first partial surface 62 of the reflection surface 42 and coupled into the left lens system channel 48L. Correspondingly, second light rays incident from the object space 11 are reflected in the second partial surface 64 of the reflection surface 42 and coupled into the right lens system channel 48R.

[0075] In a method for producing an optical system 20 of a stereo video endoscope 2 with a fixed lateral viewing direction, which comprises a side-viewing distal optical assembly 24 and a proximal optical assembly 26, the first and second prisms 32, 34 of the deflection prism group 30 of the distal optical assembly 24 are selected or arranged such that the first entrance side 36 of the first prism 32 and the reflection side 42 of the second prism 34 enclose an angle α which is greater than the total reflection angle θ C of the second prism 34.

[0076] This selection and arrangement includes not only the geometric design of the first and second prisms 32, 34 and their arrangement in the optical system 20, but also the selection of the materials or glasses used to manufacture these prisms 32, 34, which determine the respective refractive index of the prisms 32, 34.

[0077] A method for repairing a stereo video endoscope 2 with a lateral viewing direction follows a similar procedure. For example, the deflection prism group 30 of a conventional optical system 20 is replaced with a deflection prism group 30 that meets the above-mentioned requirements. It is also possible to replace the entire distal optical assembly 24 or even the entire optical system 20.

[0078] Within the scope of the invention, features marked with "in particular" or "preferably" are to be understood as optional features. List of reference symbols

[0079] 2Stereo video endoscope 4Handle 6Endoscope shaft 8Distal tip 10Entrance window 11Object space 12Distal section 14Rotary wheel 20Optical system 22Optical axis 24Distal optical assembly 26Proximal optical assembly 28Entrance lens 30Deflection prism group 32First prism 34Second prism 36First entrance side 38First exit side 40Second entrance side 42Reflection side 44Second exit side 46Exit lens 48Left lens system channel 48Right lens system channel 50Left lens group 50Right lens group 52Left image sensor 52Right image sensor 54Left channel field of view 54Right channel field of view 56Light beam 58B-down area 60L left aperture 60R right aperture 62 first partial area 64 second partial area L Longitudinal direction α Angle θ C Total reflection angle

Claims

1. An optical system (20) of a stereo video endoscope (2) with a fixed lateral viewing direction, comprising a laterally-viewing distal optical assembly (24) and a proximal optical assembly (26), wherein the proximal optical assembly (26) comprises a left lens system channel (48L) and a right lens system channel (48R) that are designed similarly, and wherein the distal optical assembly is configured to couple incident light from an object space (11) into the left lens system channel (48L) and into the right lens system channel (48R) of the proximal optical assembly (26), and wherein the distal optical assembly (24) sequentially comprises an entrance lens (28), a deflection prism group (30) and an exit lens (46) in a direction of incident light, wherein the deflection prism group (30) sequentially comprises a first prism (32) and a second prism (34) in the direction of incident light, wherein the first prism (32) comprises a first entrance side (36) and a first exit side (38) at an angle relative thereto, and wherein the second prism (34) comprises a second entrance side (40), a reflection side (42) and a second exit side (44), wherein the first entrance side (36) and the reflection side (42) enclose an angle (α) that is greater than a total reflection angle (θC) of the second prism (34), wherein a first partial surface (62) of the reflection side (42) of the second prism (34) is provided with a reflective coating, and a second partial surface (64) of the reflection side (42) is optionally uncoated or is provided with an anti-reflection coating, wherein the first and the second partial surfaces (62, 64) supplement each other to form the entire surface of the reflection side (42), characterized in that a distance between the first entrance side (36) and the reflection side (42) in the first partial surface (62) is always larger than the distance between the first entrance side (36) and the reflection side (42) in the second partial surface (64).

2. The optical system (20) according to claim 1, characterized in that the optical system (20) is configured such that incident light beams from a field of view (54L, 54R) of the optical system (20) contact the reflection side (42) of the second prism (34) at an angle that is greater than the total reflection angle.

3. The optical system (20) according to claim 2, characterized in that the optical system (20) comprises at least one aperture (60L, 60R) that borders the field of view (54L, 54R) of the optical system (20), wherein the angle (α) between the first entrance side (36) and the reflection side (42) is adjusted taking into account a material of the second prism (34) that establishes a refraction index (u2) and hence a total reflection angle (θC), and taking into account a maximum viewing angle that is established by the field of view (54L, 54R) such that total reflection of all incident light beams from the field of view ( 54L, 54R) occurs at the reflection side (42) of the second prism (34).

4. The optical system (20) according to one of claims 1 to 3, characterized in that incident first light beams from the object space (11) are reflected at the first partial surface (62) of the reflective surface (42) and are coupled into the left lens system channel (48L), and incident second light beams from the object space (11) are reflected at the second partial surface (64) of the reflective surface (42) and coupled into the right lens system channel (48R).

5. A stereo video endoscope (2) with a fixed lateral viewing direction, characterized by an optical system (20) according to one of claims 1 to 4.

6. A method for manufacturing of an optical system (20) of a stereo video endoscope (2) with a fixed lateral viewing direction, wherein the stereo video endoscope (2) comprises a laterally-viewing distal optical assembly (24) and a proximal optical assembly (26), and wherein the proximal optical assembly (26) comprises a left lens system channel (48L) and a right lens system channel (48R) that are designed similarly, and wherein the distal optical assembly (24) is configured to couple incident light from an object space (11) into the left lens system channel (48L) and into the right lens system channel (48R) of the proximal optical assembly (26), and wherein the distal optical assembly (24) sequentially comprises an entrance lens (28), a deflection prism group (30) and an exit lens (46) in a direction of incident light, wherein the deflection prism group (30) sequentially comprises a first prism (32) and a second prism (34) in the direction of incident light, wherein the first prism (32) comprises a first entrance side (36) and a first exit side (38) at an angle relative thereto, and wherein the second prism (34) comprises a second entrance side (40), a reflection side (42) and a second exit side (44), wherein the first and the second prism (32, 34) are selected or arranged such that the first entrance side (36) and the reflection side (42) enclose an angle (α) that is greater than a total reflection angle (θC) of the second prism (34), wherein a first partial surface (62) of the reflection side (42) of the second prism (34) is provided with a reflective coating, and a second partial surface (64) of the reflection side (42) is optionally left uncoated or is provided with an anti-reflection coating, wherein the first and the second partial surfaces (62, 64) supplement each other to form the entire surface of the reflection side (42), characterized in that a distance between the first entrance side (36) and the reflection side (42) in the first partial surface (62) is always larger than the distance between the first entrance side (36) and the reflection side (42) in the second partial surface (64).

7. The method according to claim 6, characterized in that the optical system (20) is provided with at least one aperture (60L, 60R) that borders the field of view (54L, 54R) of the optical system (20), wherein the angle (α) between the first entrance side (36) and the reflection side (42) is adjusted taking into account a material of the second prism (34) that establishes a refraction index (u2) and hence a total reflection angle (θC), and taking into account a maximum viewing angle that is set by the field of view (54L, 54R) such that total reflection of all incident light beams from the field of view ( 54L, 54R) occurs at the reflection side (42) of the second prism (34).

8. The method according to claim 7, characterized in that the reflection side (42) of the second prism (34) is optionally left uncoated, or is provided with an anti-reflection coating.

9. A method for repairing of a stereo video endoscope (2) with a lateral viewing direction, wherein an optical system (20) of the stereo video endoscope (2) comprises a laterally-viewing distal optical assembly (24) and a proximal optical assembly (26), and wherein the proximal optical assembly (26) comprises a left lens system channel (48L) and a right lens system channel (48R) that are designed similarly, and wherein the distal optical assembly (24) is configured to couple incident light from an object space (11) into the left lens system channel (48L) and into the right lens system channel (48R) of the proximal optical assembly (26), and wherein the distal optical assembly (24) sequentially comprises an entrance lens (28), a deflection prism group (30) and an exit lens (46) in a direction of incident light, wherein the deflection prism group (30) sequentially comprises a first prism (32) and a second prism (34) in the direction of incident light, wherein the first prism (32) comprises a first entrance side (36) and a first exit side (38) at an angle relative thereto, and wherein the second prism (34) comprises a second entrance side (40), a reflection side (42) and a second exit side (44), wherein the deflection prism group (30) is exchanged and replaced by a new deflection prism group (30), wherein the first and the second prism (32, 34) are selected or arranged such that the first entrance side (36) and the reflection side (42) enclose an angle (α) that is greater than a total reflection angle (θC) of the second prism (34), wherein a first partial surface (62) of the reflection side (42) of the second prism (34) is provided with a reflective coating, and a second partial surface (64) of the reflection side (42) is optionally left uncoated or is provided with an anti-reflection coating, wherein the first and the second partial surfaces (62, 64) supplement each other to form the entire surface of the reflection side (42), characterized in that a distance between the first entrance side (36) and the reflection side (42) in the first partial surface (62) is always larger than the distance between the first entrance side (36) and the reflection side (42) in the second partial surface (64).