Projection Optical System Back Focus and Aberration Control
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Solution Overview
Problem
Existing projection optical systems face challenges in achieving a balance between long back focus and wide angle while minimizing the size and aberration correction requirements, leading to difficulties in downsizing and maintaining image quality.
Innovation Solution
A projection optical system configuration featuring a first refractive system on the reduction side, a second refractive system on the enlargement side, and a reflective optical system in between, with specific lens group arrangements and conditions (1.5 < Bf/f < 25) to optimize focal length, back focus, and aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a projection optical system uses a refractive optical system and a reflective optical system to achieve wide angle projection, then the projection angle is improved, but the back focus becomes excessively long and the system size increases
Solution Approach 1:
The patent divides the optical system into three distinct segments: a first refractive system for initial image formation, a reflective system for light direction control, and a second refractive system for final image formation. This segmentation allows each component to be optimized independently, enabling wide angle projection while controlling back focus length by distributing optical functions across multiple components rather than relying on a single long focal length element.
Solution Approach 2:
The patent introduces a reflective optical system that operates in a different spatial dimension (reflecting light at angles) compared to the refractive systems (which primarily focus along the optical axis). This dimensional change allows the system to achieve wide angle projection by redirecting light paths through reflection rather than requiring excessively long focal lengths, effectively decoupling projection angle from back focus length.
2Illumination intensity
If the back focus is extended to achieve wide angle projection, then the projection angle is improved, but the overall system size increases making downsizing difficult
Solution Approach 1:
By segmenting the optical path into separate refractive and reflective components, the patent enables compact arrangement where the reflective system can fold the optical path, reducing the linear dimensions required. The first refractive system forms an intermediate image that can be positioned closer to the image display element, while the reflective system directs light through a shorter path to the second refractive system, achieving wide angle projection in a compact form factor.
Solution Approach 2:
The patent arranges the optical components in a nested configuration where the reflective optical system is positioned within the space defined by the refractive systems. The first refractive system, reflective system, and second refractive system are layered and integrated in a compact volume, with each component utilizing space efficiently. This nesting allows the system to achieve wide angle projection without proportionally increasing overall system volume.
3Volume of stationary object
If the system is downsized to reduce volume, then the system size is reduced, but aberration correction becomes more difficult and image quality deteriorates
Solution Approach 1:
The patent assigns specific aberration correction functions to different segments of the optical system. The first refractive system corrects aberrations at the intermediate image stage, the reflective system introduces minimal aberrations due to its geometry, and the second refractive system performs final aberration correction before image formation. This segmentation of correction functions allows effective aberration management in a compact system, as each component only needs to handle a portion of the total correction burden rather than requiring all components to be perfectly corrected.
Solution Approach 2:
The first intermediate image formed by the first refractive system serves as an intermediary that allows for aberration correction before the light reaches the reflective system. By forming this intermediate image at a controlled position, the patent enables aberration correction to be performed in a manageable stage, preventing aberration accumulation that would occur in a fully compacted single-stage system. This intermediary image formation acts as a buffer that maintains image quality despite system downsizing.
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 configuration allows for a compact projection optical system with improved aberration correction, reduced size, and enhanced image quality by efficiently addressing the balance between back focus and wide angle, while simplifying the design and reducing aberration correction needs.
Implementation Method 1
the first lens group includes a plurality of lenses, by which a first intermediate image is formed with a light beam emitted from the image display element
Implementation Method 2
the second lens group includes at least one lens, by which a second intermediate image is formed with a light beam from the first intermediate image
Implementation Method 3
the reflective optical system includes a mirror that has optical power and that is configured to reflect a light beam from the second intermediate image
Implementation Method 4
the second refractive system includes a lens that has optical power and that is configured to refract a light beam reflected by the reflective optical system
Data Source
AI summary
A projection optical system includes a first refractive system, a reflective optical system, and a second refractive system, disposed in the stated order in a direction from the reduction side toward the enlargement side, to enlarge and project an image displayed on an image display element, onto a projection surface. A first lens group of the first refractive system forms a first intermediate image with a light beam from the image display element. A second lens group of the first refractive system forms a second intermediate image with a light beam from the first intermediate image. A light beam from the second intermediate image is reflected by the reflective optical system and is then refracted by the second refractive system. A condition (1): 1.5<Bf/f<25 is satisfied, in which f represents a focal length of the entire projection optical system and Bf represents a back focus obtained by air conversion.