Aspheric Projection Lens Design for Compact Portable Projectors
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Solution Overview
Problem
Existing projection lenses for portable projectors have limitations such as a small angle of view, insufficient back focus for color composition and separation of illumination light, and inadequate consideration for aspherizing, which affects their compactness, lightweight design, and telecentric characteristics.
Innovation Solution
A projection lens system comprising a first aspheric positive lens, a second concave negative lens, a third convex positive lens, and a fourth positive lens, arranged telecentrically on the reduction side, with specific refractive index and Abbe number constraints to ensure compactness, low cost, and high optical performance, along with an aperture to restrict light rays and improve telecentricity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the number of lenses is reduced for portability, then device complexity and weight are reduced, but optical performance and telecentric characteristics deteriorate
Solution Approach 1:
The patent applies aspheric surfaces to lens elements, changing the geometric parameters from spherical to aspheric profiles. This allows a reduced number of lenses to achieve the same optical performance, enabling telecentric characteristics and proper back focus with fewer components while maintaining image quality
Solution Approach 2:
The patent specifically uses aspheric lens surfaces instead of traditional spherical surfaces. The aspheric profiles enable better control of light rays with fewer lens elements, achieving telecentric reduction side characteristics and adequate back focus while reducing overall device complexity and weight for portable applications
2Area of stationary object
If the angle of view is increased for larger projection images, then projection size is improved, but lens size and complexity increase
Solution Approach 1:
The patent employs aspheric surfaces on lens elements to change the geometric parameters of the optical system. This enables a compact lens design that achieves a wide angle of view (25-30 degrees) and large projection image size without proportionally increasing lens diameter or complexity
Solution Approach 2:
The patent divides the optical function across strategically positioned lens elements with specific aspheric profiles. The first lens element with aspheric surface handles initial light convergence, while subsequent elements manage field curvature and distortion, enabling wide-angle projection with controlled overall size
3Reliability
If back focus is increased for color composition and separation, then optical performance is improved, but device length increases
Solution Approach 1:
The patent uses aspheric lens surfaces to change the focal parameters and light convergence characteristics. This enables adequate back focus distance (0.06 to 0.12 times the focal length) for color composition and separation while keeping the overall device length compact for portable projectors
Solution Approach 2:
The patent positions the aperture stop as an intermediary element between the first lens element and subsequent elements. This intermediary structure helps control chief ray angles and enables adequate back focus for color optics while maintaining compact overall device length through optimized light path management
4Length of moving object
If aspherizing is applied to the first lens for downsizing and brightening, then compactness is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies aspheric surfaces selectively to specific lens elements (particularly the first lens element) rather than all elements. This local application achieves downsizing and brightening benefits where most needed while limiting the number of expensive aspheric surfaces, thereby controlling manufacturing cost
Solution Approach 2:
The patent uses aspheric profiles on the first lens element to enable compact lens size and improved brightness. The aspheric curvature allows better light gathering and convergence in a smaller package. The patent balances this manufacturing complexity by limiting aspheric surfaces to only the most critical elements
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 results in a compact, lightweight, and cost-effective projection lens that secures sufficient back focus for illumination separation and color composition, while maintaining high optical performance and telecentric characteristics, enabling the creation of portable and efficient projection-type display apparatus.
Implementation Method 1
a first lens having a positive power and at least one surface that is an aspheric surface
Implementation Method 2
enlarges and projects images formed on a conjugation surface on a reduction side onto a conjugation surface on a magnification side
Data Source
AI summary
To provide a projection lens that is compact, lightweight, low-cost, and readily portable, a first lens having a positive power and at least one surface that is an aspheric surface; a second lens having a negative power and having a concave surface on the magnification side; a third lens having a positive power and having a convex surface on the reduction side; and a fourth lens having a positive power are arranged in order from the magnification side. In addition to arranging the lenses telecentrically on the reduction side, the following formulas are satisfied simultaneously, and images formed on the conjugation surface on the reduction side are enlarged and projected on the conjugation surface on the magnification side: formula (A) 0.8<Bf/f; formula (B) 1.1<f1/f<1.6; formula (C) Nd1<1.7, formula (D) vd1<35.