Stereo-Video Endoscope Prism Angle Design Suppresses Ghost Images
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Solution Overview
Problem
Stereo video endoscopes with a fixed lateral viewing direction are prone to ghost images due to quadruple reflections in the deflection prism group, which are caused by light beams entering at large angles to the optical axis.
Innovation Solution
The optical system is designed with a deflection prism group comprising prisms where the first entrance side and reflection side of the second prism form an angle greater than the total reflection angle, and the reflection side has a partial surface with a reflective layer and another partial surface that is uncoated or anti-reflective, optimizing the distance and angle to prevent multiple reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a deflection prism group with cemented prisms is used to redirect light at an angle to the longitudinal axis, then the lateral viewing direction is achieved, but ghost images are generated due to quadruple reflections of peripheral light rays
Solution Approach 1:
The reflection side of the second prism is divided into different zones with different optical properties: a first zone with a reflective coating for total internal reflection of field-of-view light rays, and a second zone without coating or with anti-reflective coating for allowing peripheral light rays to exit without reflection. This local differentiation eliminates ghost images while maintaining the lateral viewing function.
Solution Approach 2:
The reflection side surface is segmented into multiple functional areas: a first partial surface with reflective coating and a second partial surface without or with anti-reflective coating. This segmentation allows different light rays to be treated differently, preventing the quadruple reflection pathway that causes ghost images.
2Reliability
If the first entrance side and reflection side form an angle greater than the total reflection angle, then total internal reflection is achieved for light rays within the field of view, but the design complexity of the prism increases
Solution Approach 1:
The angle between the first entrance side and the reflection side is specifically designed to be greater than the total reflection angle (critical angle) for the prism material. This parameter change ensures that light rays within the field of view undergo total internal reflection at the reflection side, improving reliability while the angle constraint is managed through precise geometric design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses ghost images by ensuring total internal reflection for light rays within the field of view while allowing peripheral rays to exit without creating unwanted reflections, thereby enhancing the 3D imaging quality.
Implementation Method 1
the first entrance side and the reflection side enclose an angle that is greater than a total reflection angle of the second prism
Implementation Method 2
a first partial surface of the reflection side of the second prism is provided with a reflective layer
Implementation Method 3
a second partial surface of the reflection side is optionally uncoated or provided with an anti-reflective coating
Data Source
Figure 1
Figure 2
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AI summary
The invention relates to an optical system (20) of a stereo-video endoscope (2) having a fixed lateral viewing direction. The optical system (20) comprises a distal optical assembly (24) and a proximal optical assembly (26), wherein the latter comprises a left and a right lens system channel (48L, 48R). Light incident from an object space (11) is coupled into the left and right lens system channels (48L, 48R) of the proximal optical assembly (26), wherein the distal optical assembly (24) configured for this purpose comprises an entrance lens (28), a deflection prism group (30) and an exit lens (46) successively in the light incidence direction. The deflection prism group (30) comprises a first and a second prism (32, 34). The first prism comprises a first entrance side (36), and the second prism (34) comprises a reflection side (42). The entrance side (36) and the reflection side (42) form an angle (α) that is greater than the total internal reflection angle (θc) of the second prism (34).