Magnified Projection Optical System with Long Back Focus
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Solution Overview
Problem
There is a trade-off relationship between achieving a wider angle and longer back focus in projection optical systems, making it difficult to implement systems with both high performance and reduced chromatic aberration, and existing solutions do not adequately address the correction of aberration.
Innovation Solution
A magnified-projection optical system is designed with a specific configuration that includes a projection optical system and relay optical system, where the negative group is positioned closest to the screen, and a positive group is placed after the negative group to correct lateral chromatic aberration, allowing for a long back focus and reduced chromatic aberration despite a short focal distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the projection optical system is designed with a wider angle to project images at a short distance, then the projection distance is reduced, but the back focus becomes insufficient
Solution Approach 1:
The projection optical system is divided into multiple lens groups (first through fifth lens groups) with different optical powers arranged in sequence. This segmentation allows each group to contribute differently to the overall optical performance, enabling wide-angle projection while maintaining sufficient back focus distance.
Solution Approach 2:
Different lens groups are assigned specific functions: negative-powered lens groups are positioned to extend back focus, while positive-powered groups provide focusing capability. The fifth lens group specifically addresses lateral chromatic aberration, creating local optical quality improvements throughout the system.
2Area of stationary object
If the projection optical system uses a short focal distance to achieve wide angle, then the projection coverage is improved, but chromatic aberration increases
Solution Approach 1:
The fifth lens group is specifically designed with positive optical power and positioned to correct lateral chromatic aberration caused by the wide-angle first lens group. This localized correction maintains high image quality across the entire projection coverage area.
Solution Approach 2:
The optical system uses multiple lens materials with different Abbe numbers (dispersion properties) to correct chromatic aberration. By combining lenses with varying dispersive characteristics, the system achieves color accuracy across the wide projection angle.
3Measurement precision
If the projection optical system is designed for high resolution to match close-packed display elements, then image clarity is improved, but the system complexity increases
Solution Approach 1:
The optical system is divided into five functional lens groups, each contributing to different aspects of image quality. This modular segmentation allows for systematic correction of various aberrations while maintaining manageable system complexity.
Solution Approach 2:
The system optimizes multiple parameters including focal lengths, spacing between lens groups, and refractive indices to achieve high resolution. By carefully controlling these parameters, the system delivers sharp images matching close-packed display elements without excessive complexity.
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 system achieves a high-performance magnified-projection optical system with a long back focus and reduced chromatic aberration, enabling clear image projection over a wide angle with improved MTF performance.
Implementation Method 1
a relay optical system and a projection optical system which are arranged in this order as viewed from the screen
Implementation Method 2
projection optical system having a very long back focus... a magnified-projection optical system... wider angle (shorter focusing)
Implementation Method 3
a positive group is placed after the negative group to correct lateral chromatic aberration
Data Source
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AI summary
Provided is a magnified-projection optical system, which can retain a considerably long back focus although a focal length is short and which has a small chromatic aberration. The optical system comprises a projecting optical system, a relay optical system and a display element, which are sequentially arrayed from a screen side along the optical axis. The projecting optical system enlarges and projects the image, which has been linearly focused by the relay optical system, on the screen, and includes a negative group and a positive group arrayed sequentially from the screen side and having a negative optical power and a positive optical power, respectively. The optical system satisfies the following conditional relations of |Fb/F| > 10 and 0.5 < |F/Fp| < 2.0, wherein Fb: the back focus of the whole optical system including the projecting optical system and the relay optical system, F: the focal length of the whole optical system, and FP: the focal length of the projecting optical system