Angled Connecting Surface Porro Prism Beam Offset Reduction
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Solution Overview
Problem
Porro prisms exhibit significant beam offset between incoming and outgoing beams, leading to a bulky design in binoculars and telescopes due to the quadruple beam deflection, which results in a z-shaped appearance and potential vignetting issues.
Innovation Solution
The connecting surface of the Porro prism is angled relative to the optical axes of the beam path sections passing through the exposed entry and exit surfaces, reducing beam offset by narrowing the beam cross-section towards the center while maintaining light entry and exit cross-sections on the outer surfaces, and allowing for further reduction through parallel shifting of inverting prisms and adjusting inclined surfaces to bring optical axes closer together.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional Porro prism design with perpendicular connecting surface is used, then easy manufacturing and simple structure are achieved, but beam offset is large causing bulky design
Solution Approach 1:
The patent changes the geometric parameter of the connecting surface from perpendicular to inclined at a specific angle relative to the optical axes. This parameter modification allows the beam path to be compressed, reducing beam offset while maintaining the necessary image inversion function, thereby resolving the contradiction between structural simplicity and compactness.
2Length of moving object
If beam cross section is narrowed towards center to reduce beam offset, then beam offset is reduced, but vignetting occurs reducing brightness
Solution Approach 1:
The patent applies different geometric characteristics to different regions of the beam path. The connecting surface is designed with specific angular relationships that create a gradual narrowing of the beam cross-section rather than a abrupt reduction. This local geometric optimization allows beam offset reduction while minimizing vignetting effects, as the beam transitions smoothly through the prism structure.
3Length of moving object
If inverting prisms are parallel-shifted to bring optical axes closer, then beam offset is further reduced, but prism length increases
Solution Approach 1:
The patent utilizes the angular dimension of the connecting surface to achieve beam compression. By introducing the angular parameter of the connecting surface relative to the optical axes, the system can reduce beam offset without requiring excessive parallel shifting of prisms, thus avoiding excessive length increase while achieving compactness through multi-dimensional geometric optimization.
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 achieves a small beam offset without significant disadvantages, such as vignetting, and enables the possibility of coupling light in or out of the beam path for additional applications like measuring devices, while maintaining exact image rotation.
Implementation Method 1
the connecting surface can therefore also be used to couple a portion of light out of the beam path and/or into it by making it partially reflective
Implementation Method 2
Porro prisms have extremely low losses due to the small number of reflections and can be produced inexpensively by using, in particular, totally reflecting inclined surfaces instead of mirror layers
Data Source
Figure 1a~1d
Figure 2a~2d
Figure 3a~3d
AI summary
Porro prism (1', 1", 1'') of the second kind, consisting of at least two interconnected reversing prisms (4, 5), each providing two reflective inclined surfaces (6-9) for the beam path (2, 15, 17, 16, 3) between an entrance and an exit surface (10-13), wherein the exit surface (11, 12) of one and the entrance surface (12, 11) of the other reversing prism (4, 5) form their connecting surface (14), characterized in that the connecting surface (14) lies inclined to the optical axes (2, 3) of those sections of the beam path (2, 15, 17, 16, 3) which pass through the exposed entrance and exit surfaces (10, 13) of the reversing prisms (4, 5).