Non-Telecentric Projection Optical System for Compact Close-Range Imaging
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Solution Overview
Problem
Conventional projection optical systems face challenges in achieving a compact design while maintaining optical quality, particularly in close-range projection applications, where increasing the angle of view requires larger lens diameters and increased system size, and telecentric systems often result in larger diameters near the image display element.
Innovation Solution
A non-telecentric projection optical system comprising a first lens group with positive refractive power, a second lens group with positive refractive power, a third lens group with negative refractive power, a fourth lens group with aspheric or free-form surfaces, and a concave mirror, arranged in order, which allows for a compact design without increasing the total system size by effectively managing light beam convergence and divergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the angle of view of a conventional projection optical system is increased to reduce the distance from the screen, then the projection distance is reduced, but the outer diameter of the lens near the screen must be increased, resulting in an increased total size of the projector
Solution Approach 1:
The projection optical system is divided into multiple lens groups (first through fourth lens groups) with different refractive powers arranged in sequence. This segmentation allows each group to contribute differently to light beam control, enabling compact design while achieving close-range projection without requiring large individual lens diameters.
Solution Approach 2:
The patent introduces a non-telecentric optical configuration where the aperture stop is positioned away from the center of the refractive optical system, creating asymmetric light beam paths in the optical dimension. This dimensional change in optical path management allows for reduced lens diameters while maintaining close-projection capability.
2Stability of the object's composition
If a telecentric projection optical system is used, then light beams are entirely condensed at a position away from the image display element, but the diameter of a lens near the image display element tends to increase
Solution Approach 1:
Instead of using a telecentric configuration where the aperture stop is at the center, the patent inverts the approach by using a non-telecentric configuration with the aperture stop positioned nearer to the image display element than the center. This inversion allows light beams to be condensed at a position away from the image display element while avoiding the penalty of increased lens diameter at that location.
3Ease of operation
If a non-telecentric projection optical system is used, then light beams leave from the image display element and spread naturally, but the diameter of a lens at a position near the concave mirror is increased
Solution Approach 1:
Different lens groups are assigned different refractive powers (positive or negative) to locally optimize their function. The fourth lens group with aspheric or free-form surfaces provides localized correction of light beam spread, enabling the system to maintain non-telecentric operation while controlling lens diameter growth near the concave mirror through localized optical quality enhancement.
4Length of moving object
If a projection optical system with throw ratio less than 0.35 is used, then projection in highly close range is achieved, but it becomes necessary to separate light beams directed to different parts of the projected image certainly and conduct different control, increasing lens diameter and mirror size
Solution Approach 1:
The fourth lens group incorporates aspheric or free-form surfaces that provide curved optical paths for light beams. This curvature capability allows the system to handle the complex light beam separation required for ultra-close projection (throw ratio < 0.35) without requiring excessively large lens diameters or mirror sizes, as the curved surfaces efficiently redirect beams to different image regions.
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 enables projection in a highly close range with improved optical properties, including reduced lens diameters and mirror sizes, while maintaining uniform illuminance distribution and correcting distortion and curvature of field aberrations.
Implementation Method 1
a projection optical system which is non-telecentric with respect to an image display element
Implementation Method 2
a first lens group configured to include at least one lens and have a positive refractive power
Data Source
AI summary
Disclosed is a projection optical system, including a first lens group configured to include at least one lens and have a positive refractive power, a second lens group configured to include at least one lens and have a positive refractive power, a third lens group configured to include at least one lens and have a negative refractive power, a fourth lens group configured to include at least one lens configured to have an aspheric surface or a free-form surface, and a concave mirror, wherein the first lens group, the second lens group, the third lens group, the fourth lens group, and the concave mirror are arranged in order and the projection optical system is a non-telecentric optical system.