Seven-Group Projection System Back Focal Length Extension
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Solution Overview
Problem
Existing seven-group projection systems face challenges in achieving a long enough back focal length to accommodate a light combining prism and contrast compensation elements while maintaining sufficient brightness, especially in three-panel projectors.
Innovation Solution
A seven-group projection system configuration with specific refractive power arrangements and lens group compositions, including aspheric lenses, to increase back focal length and suppress aberrations, allowing for the incorporation of additional optical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a seven-group projection system is used, then optical performance is improved, but the back focal length is insufficient to accommodate additional optical components
Solution Approach 1:
The patent applies parameter changes by carefully selecting the dispersion values (νd) of specific lenses in the seven-group configuration. The conditional expression νdR - νdF < 30 transforms the optical parameters of the system to shift the negative refractive power portion toward the magnifying side, thereby extending the back focal length without compromising optical performance
Solution Approach 2:
The patent employs composite lens designs, particularly in the sixth lens group which combines a biconcave lens and a biconvex lens bonded together to form a doublet. This composite structure allows simultaneous correction of chromatic aberrations and extension of back focal length
2Adaptability or versatility
If additional optical components are added, then functionality is improved, but device complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-configuring the seven-group lens system with specific dispersion parameter relationships that inherently create sufficient back focal length. This preliminary optimization of the projection system allows additional components like light combining prisms and contrast compensation elements to be added without requiring further complex redesign
3Adaptability or versatility
If zooming function is added, then versatility is improved, but aberration control becomes more difficult
Solution Approach 1:
The patent applies segmentation by dividing the projection system into seven distinct lens groups with specific refractive power assignments. This segmentation allows independent optimization of each group's function: the first and fourth groups with negative refractive power control zooming, while the other groups maintain image quality and correct aberrations across the zoom range
Solution Approach 2:
The patent implements multi-functionality through the sixth lens group's doublet structure, which simultaneously corrects chromatic aberrations resulting from zooming, suppresses sagittal coma, and maintains telecentricity. This single composite structure performs multiple aberration correction functions that would otherwise require separate components
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 configuration ensures a longer back focal length, enabling the placement of cross dichroic prisms and other members, while maintaining high optical performance and producing high-quality images across various zoom ranges.
Implementation Method 1
a lens closest to the enlargement side in the first lens group is an aspheric lens made of a resin
Implementation Method 2
the sixth lens group is formed of a combination of a biconcave lens and a biconvex lens bonded to each other to form a doublet
Implementation Method 3
νdR that is a dispersion value of a lens that forms the seventh lens group out of the seven lens groups and is closest to a reduction side and νdF that is a dispersion value of a lens that forms the first lens group out of the seven lens groups and is closest to the magnifying side satisfy a following conditional expression: νdR−νdF30
Implementation Method 4
the fifth lens group is formed of an aspheric lens made of glass
Implementation Method 5
spherical aberrations and coma flare can be suppressed
Data Source
AI summary
A projection system including seven lens groups sequentially arranged from an enlargement side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, a fifth lens group having positive refractive power, a sixth lens group having positive refractive power, and a seventh lens group having positive refractive power, wherein νdR that is a dispersion value of a lens that forms the seventh lens group out of the seven lens groups and is closest to a reduction side and νdF that is a dispersion value of a lens that forms the first lens group out of the seven lens groups and is closest to the enlargement side satisfy a following conditional expression: 5<νdR−νdF<30.