Compact Objective Lens Assembly Using Folded Optical Path
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Solution Overview
Problem
Conventional objective lens assemblies for VNIR and LWIR cameras are too long for hand-held and helmet-mounted applications, causing forward projection issues and interfering with user movement, and are prone to chromatic aberration and manufacturing errors due to complex asymmetric free-form aspheric surfaces.
Innovation Solution
A compact objective lens assembly using two prisms that fold and rotate the optical path to conform to a helmet surface, reducing length and susceptibility to alignment errors, with rotational symmetric aspheric surfaces and asphero-diffractive elements for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional objective lens assemblies are used for VNIR and LWIR cameras, then the optical system can detect images in visible and infrared regions, but the lens assembly becomes too long causing forward projection issues and interfering with user movement
Solution Approach 1:
The patent introduces a prism element that folds the optical path at an angle, transitioning from a linear optical path to a bent three-dimensional path. This allows the light to travel through a longer effective optical path length while the physical projection along the helmet axis remains compact, resolving the contradiction between optical path length and forward projection length.
Solution Approach 2:
The prism acts as an intermediary optical element between the lens assembly and the image detector. It mediates the optical path by reflecting and redirecting light at specific angles, enabling the system to achieve the required focal length and field of view while minimizing the forward projection distance that would otherwise interfere with user movement.
2Adaptability or versatility
If conventional objective lens assemblies with complex asymmetric free-form aspheric surfaces are used, then the optical system can achieve required focal length and field of view, but manufacturing precision deteriorates due to susceptibility to alignment errors
Solution Approach 1:
The patent employs asymmetric prism geometries with specific angular relationships between the prism faces and the optical axis. These asymmetric configurations are designed to fold the optical path in a way that achieves the required focal length and field of view while providing inherent tolerance to alignment errors through the geometric relationship between the prism surfaces and the lens elements.
Solution Approach 2:
The patent modifies the optical parameters by introducing the prism element with specific refractive index and geometric angles. This changes the overall optical path length and folding configuration, allowing the system to achieve the required performance while reducing sensitivity to manufacturing tolerances and alignment errors through optimized parameter selection.
3Length of stationary object
If the optical path length is reduced for helmet-mounted applications, then the forward projection is minimized, but the optical system becomes more complex requiring prisms and folded paths
Solution Approach 1:
The patent uses a prism to introduce angular folding into the optical path, moving from a simple linear arrangement to a bent three-dimensional configuration. This allows the optical path to be shortened in the forward projection direction while maintaining the necessary optical elements and functionality, accepting increased device complexity as a trade-off for reduced forward projection.
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
The solution provides a compact, accurate, and efficient optical system that minimizes forward projection and manufacturing complexities, enabling effective use in helmet-mounted applications with reduced chromatic aberration and improved field of view.
Implementation Method 1
two prisms longitudinally separated relative to a structure (such as a helmet or other headgear), and arranged in an angular relationship to one another such that an optical path through the system is folded to conform to a surface of the structure
Data Source
AI summary
A high-performance image-forming optical objective lens made compact and thin, particularly in the object side direction, by twice folding the optical path by means of two prism lenses longitudinally separated and arranged in an angular relationship to one another. The prisms have entrance and exit faces each of which is constructed of a curved surface having optical power, as well as having a rotationally symmetric polynomial aspheric attribute. The image-forming optical objective is particularly suited to helmet-mounted applications wherein the angular means for folding the optical path provides for an optical objective configuration that closely conforms to the exterior surface contour of the helmet, while providing a minimal forward projection in object space from the helmet.