Projection Lens with Convex Mirror for Trapezoidal Distortion Correction
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Solution Overview
Problem
Conventional projectors using oblique projection methods suffer from trapezoidal distortion, which is typically corrected using software, resulting in reduced resolution and brightness, or through hardware adjustments that increase the projector's size.
Innovation Solution
An imaging system and projection device with a projection lens that includes a lens group and a convex mirror, where at least one of the lens elements is a freeform surface lens element, configured to reduce trapezoidal distortion without software correction, maintaining image quality and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If software correction is used to reduce trapezoidal distortion, then distortion-free projection is achieved, but resolution and brightness are reduced
Solution Approach 1:
The patent replaces software correction with an optical solution using a projection lens comprising a lens group and a convex mirror. The freeform surface lens elements in the lens group optically correct the trapezoidal distortion through their specialized geometry, eliminating the need for post-processing software correction that degrades image quality.
Solution Approach 2:
The patent employs freeform surface lens elements with specifically designed refractive powers and surface geometries. By changing the optical parameters of the lens elements (refractive power, surface curvature, element spacing), the system achieves geometric correction of the projection image while maintaining full resolution and brightness.
2Shape
If hardware correction by moving the projection lens is used to reduce trapezoidal distortion, then distortion-free projection is achieved, but the projector size increases
Solution Approach 1:
The patent uses a convex mirror with a specifically designed curvature radius (R ≥ 50mm) and freeform surface lens elements with curved geometries. These curved optical surfaces enable compact folding of the optical path, allowing geometric correction without requiring a larger physical projector housing.
Solution Approach 2:
The patent integrates the convex mirror and lens group in a nested configuration where the convex mirror is positioned between the lens group and the magnification side. This nested arrangement allows multiple optical elements to occupy overlapping spatial volumes, reducing the overall projector footprint while maintaining correction functionality.
3Volume of moving object
If oblique projection is used to reduce usage space, then projector compactness is improved, but trapezoidal distortion occurs
Solution Approach 1:
The patent employs asymmetric optical design through freeform surface lens elements with different refractive powers on different sides (first side facing convex mirror, second side facing light valve). This asymmetric geometry compensates for the asymmetric oblique projection angle, correcting distortion while maintaining compact projector dimensions.
Solution Approach 2:
The patent introduces a convex mirror as an intermediary optical element between the lens group and the projection path. This intermediary component redirects and corrects the oblique projection beam, transforming the distorted oblique projection into a geometrically accurate image while preserving the compact projector form factor.
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 effectively reduces trapezoidal distortion in projectors, maintaining image resolution and brightness while minimizing the projector's size, as demonstrated by the use of freeform surface lens elements and specific optical configurations.
Implementation Method 1
The convex mirror is configured on an optical path between the lens group and the magnification side
Implementation Method 2
At least one of the third lens element and the fourth lens element is a freeform surface lens element
Data Source
AI summary
An imaging system, including a light valve and a projection lens, is provided. The projection lens has a reduction side and a magnification side, and includes a lens group and a convex mirror. The light valve is configured on the reduction side. The projection lens is configured to image the beam from the light valve on a projection surface, and the projection surface is configured on the magnification side. There is an included angle between the projection surface and a light receiving surface. The lens group is configured on an optical path between the magnification side and the reduction side, and includes first to seventh lens elements sequentially arranged from the magnification side to the reduction side. The refractive powers of the first to seventh lens elements are respectively negative, negative, positive, positive, negative, positive, and positive. The convex mirror is configured on an optical path between the lens group and the magnification side. A projection device, including the imaging system, is also provided.