Ultra-Short Throw Projection Lens With Intermediate Image Aberration Control
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Solution Overview
Problem
Existing short throw projectors face challenges in maintaining projection imaging quality when the projection distance is shortened, as the shorter focal length leads to increased distortion and reduced field of view.
Innovation Solution
An ultra short throw projection lens design comprising a first and second lens group, with specific optical parameters and aspherical lenses, and an optional reflective element to change the optical axis, ensuring optimal imaging quality and field of view while minimizing aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the focal length of the projection lens is shortened to reduce projection distance, then the projection distance is reduced, but the field of view increases and distortion increases strongly
Solution Approach 1:
The projection lens is divided into multiple lens groups (first lens group with positive power and second lens group with negative power) rather than a single lens element. This segmentation allows each group to contribute differently to the overall optical function, enabling the system to achieve ultra-short throw ratio while controlling distortion through the coordinated action of multiple groups with opposite powers.
Solution Approach 2:
Different regions of the optical system are assigned different properties: the first lens group has positive optical power for convergence, the second lens group has negative optical power for divergence and field expansion, and aspherical surfaces are selectively applied to specific lens elements. This local differentiation of optical properties enables simultaneous achievement of short focal length and distortion control.
2Length of moving object
If the focal length of the projection lens is shortened to reduce projection distance, then the projection distance is reduced, but the field of view increases
Solution Approach 1:
The lens system is segmented into at least two lens groups with opposite optical powers. The second lens group with negative power specifically contributes to expanding the field of view while the first lens group with positive power maintains the ultra-short focal length, thereby resolving the contradiction between reduced projection distance and increased field of view.
Solution Approach 2:
The patent employs aspherical lens surfaces with specifically designed curvature parameters to control the field of view. The aspherical parameters are optimized to achieve a wide field of view (60°≤FOV≤155°) while maintaining the ultra-short throw ratio, changing the geometric parameters of the lens surfaces to simultaneously achieve compact size and wide viewing angle.
3Length of moving object
If the focal length of the projection lens is shortened to reduce projection distance, then the projection distance is reduced, but the imaging quality deteriorates due to stronger distortion
Solution Approach 1:
By segmenting the lens into multiple groups with different optical powers and characteristics, the patent can correct various aberrations (distortion, field curvature, chromatic aberration) through the combined effect of each group. The positive and negative lens groups work together to compensate for each other's aberrations, maintaining high imaging quality despite the ultra-short focal length.
Solution Approach 2:
The patent utilizes aspherical lens surfaces instead of simple spherical surfaces. The aspherical parameters are specifically optimized to control and correct optical aberrations including distortion and field curvature, thereby maintaining high imaging quality in the ultra-short throw projection lens system.
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 design achieves a shortened projection distance with improved imaging quality, controlled aberrations, and a larger field of view, maintaining high performance across various image heights and wavelengths.
Implementation Method 1
the first lens group includes a first aspherical lens with a concave surface facing the image source side, and a second aspherical lens with a concave surface facing the imaging side
Implementation Method 2
the ultra-short throw projection lens further includes a reflective element located between the first lens group and the second lens group for changing the direction of the optical axis
Data Source
AI summary
An ultra short throw projection lens sequentially comprising: a first lens group and a second lens group, the image source is first projected into an intermediate image by the second lens group, then the intermediate image is projected into a final image on the screen side by the first lens group, which complies with 0.23≤TR≤0.45 and 1.6≤|IMH2|/|IMH1|≤3, TR is the throw ratio of the ultra-short throw projection lens, IMH1 is the maximum image height of the image source, IMH2 is the maximum image height of the intermediate image, the second lens group includes an aperture, and the aperture has an F/# between 1.6˜3.2.