Projection Lens Design for Compact Front Display
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing projection lenses for front type projection display devices are limited by large size and inability to achieve compactification and wider viewing angles due to the need for long optical axis length and thermal issues, which are not addressed by current wide-angle lenses designed for rear type devices.
Innovation Solution
A projection lens design featuring a first lens group with negative refractive power and a second lens group with positive refractive power, including aspheric lenses and cemented lenses, optimized with specific conditional expressions to ensure telecentricity, suitable back focal length, and aberration correction, allowing for compactification and wider viewing angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a prism or mirror for turning back optical axis is arranged in the lens system to reduce cabinet thickness in rear type devices, then the back focal length is extended, but the spatial size of the device increases
Solution Approach 1:
The patent inverts the conventional lens arrangement by placing the first lens group with negative refractive power at the object side and the second lens group with positive refractive power at the image side, opposite to the traditional configuration. This inversion enables the lens to achieve telecentricity on the reduction side with a shorter optical axis length, eliminating the need for additional space-consuming optical elements while maintaining the required back focal length for thermal management and color synthesis.
2Volume of moving object
If the optical axis length is shortened for compactification in front type devices, then the viewing angle is limited, but the device size is reduced
Solution Approach 1:
The patent changes the refractive power distribution parameters by assigning negative refractive power to the first lens group and positive refractive power to the second lens group, with specific conditional expressions controlling the ratio of their focal lengths. This parameter optimization enables the lens to achieve a wide viewing angle of 100 degrees or more while maintaining a compact optical axis length suitable for front type projection devices.
3Reliability
If telecentricity is achieved with entrance pupil located far enough on the reduction side, then spectral characteristic stability is improved, but the back focal length increases
Solution Approach 1:
The patent segments the lens system into two distinct lens groups with different refractive power characteristics. The first lens group with negative refractive power and the second lens group with positive refractive power work together to achieve telecentricity on the reduction side while controlling the back focal length. This segmentation allows independent optimization of telecentricity and back focal length parameters.
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 high-resolution, compact projection lens system with improved aberration correction and wider viewing angles, suitable for front type projection display devices, while avoiding thermal issues and maintaining optical performance throughout the focusing range.
Implementation Method 1
An aspheric lens is arranged on the most magnification side of the first lens group
Implementation Method 2
a first lens group having negative refractive power and a second lens group having positive refractive power
Data Source
AI summary
A projection lens includes, in order form a magnification side: a first lens group having negative refractive power; and a second lens group having positive refractive power. An aspheric lens is arranged on the most magnification side of the first lens group. The conditional expressions 3<Bf/f and 0.4<H/L are satisfied, where f denotes a focal length of the projection lens, Bf denotes an air-converted back focal length, H denotes a height of a principal ray at the maximum angle of view on a plane which is orthogonal to an optical axis and which passes through point A, and L denotes a length from the point A to a vertex of a lens surface on the most reduction side on the optical axis. Here, the point A is a vertex of a lens surface on the most magnification side on the optical axis.