Projection Lens Device with Reflection Mirror for Back Focal Length
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Solution Overview
Problem
Existing projection lens devices for rear projection display apparatuses face challenges in achieving a long back focal length, wide angle of view, and high projection performance while minimizing manufacturing costs, particularly due to the use of prisms which increase costs and do not allow for miniaturization.
Innovation Solution
A projection lens device configuration with a first lens group having negative refractive power and a second lens group with positive refractive power, utilizing a maximum air space and an inexpensive reflection mirror to deflect the optical path, and incorporating aspheric surfaces and cemented lenses to correct aberrations and achieve telecentricity on the reduction side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a prism is used as a reflective element to deflect the optical path, then the optical path can be deflected, but the manufacturing cost increases
Solution Approach 1:
The patent replaces expensive prisms with inexpensive reflection mirrors to deflect the optical path. This substitution directly addresses the technical contradiction by using a cheaper reflective element (reflection mirror) that can achieve the same optical path deflection function, thereby reducing manufacturing cost while maintaining the required optical functionality.
2Volume of moving object
If the projection lens device is miniaturized, then the display apparatus size decreases, but the back focal length becomes shorter
Solution Approach 1:
The patent uses a reflection mirror to deflect the optical path at an angle, effectively utilizing spatial dimensions differently. By introducing an optical path deflection mechanism, the patent can achieve a longer back focal length within a more compact form factor, as the light travels a longer path through the lens groups while the physical device dimensions remain smaller.
Solution Approach 2:
The patent employs a movable reflection mirror that can be positioned at different locations within the maximum air space between the first and second lens groups. This dynamic positioning capability allows for adjustment of the optical path length and back focal length while maintaining miniaturization, enabling the device to adapt its optical characteristics within a compact form factor.
3Reliability
If the angle of view is increased to 105 degrees or more, then the projection performance improves, but the lens design becomes more complex
Solution Approach 1:
The patent divides the projection lens device into two distinct lens groups: a first lens group with negative refractive power and a second lens group with positive refractive power. This segmentation allows each group to be optimized for specific functions, with the first group handling wide-angle light rays and the second group focusing the image, thereby achieving a wide angle of view (105 degrees or more) while managing design complexity through functional division.
Solution Approach 2:
The patent applies aspheric surfaces specifically to certain lens elements within the lens groups to correct aberrations that arise from the wide angle of view. By locally applying aspheric geometry where needed rather than to all surfaces, the patent achieves high projection performance with a wide angle of view while controlling overall design complexity through targeted application of complex surface geometries.
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 secures a long back focal length, wide angle of view, and high projection performance while reducing manufacturing costs by using a reflection mirror instead of prisms, allowing for miniaturization and effective aberration correction.
Implementation Method 1
inserting a reflective element into the projection lens device... employing an inexpensive reflection mirror as a reflective element for deflecting an optical path
Implementation Method 2
The first lens group has at least one aspheric surface... well correcting various aberrations
Data Source
AI summary
A projection lens device includes, in order from a magnification side, a first lens group G1 having a negative refractive power, and a second lens group G2 having a positive refractive power. The projection lens device is substantially telecentric on a reduction side thereof. The second lens group G2 includes a three-element cemented lens L10 to L12 formed by cementing three lens elements. A space between the first lens group G1 and the second lens group G2 is set as the maximum inter-lens space (the maximum air space) so that a reflection mirror 4 can be inserted. Also, the projection lens device satisfies eight conditional expressions.