Projection Zoom Lens Aberration Correction via Multi-Group Segmentation
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Solution Overview
Problem
Current projection-type zoom lenses fail to adequately meet the demands for high zoom ratio, wide angle of view, and sufficient back focus, leading to inadequate correction of aberrations such as spherical aberration and field curvature.
Innovation Solution
A zoom lens configuration comprising multiple lens groups with specific refractive powers and movements, including a negative fourth lens group with a concave surface and a fifth lens group with a combination of positive and negative lenses, arranged to satisfy specific focal length and Abbe number conditions, ensuring telecentricity and effective aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the zoom ratio is increased to meet the demand for high zoom ratio, then the image size change capability is improved, but the back focus length becomes insufficient for inserting a prism
Solution Approach 1:
The zoom lens is divided into six lens groups (G1-G6) with different refractive powers and movement characteristics. The first lens group (G1) with negative refractive power and the sixth lens group (G6) with positive refractive power are fixed during zooming, while the intermediate lens groups (G2-G5) move to change magnification. This segmentation allows the front and back focal points to be independently controlled, maintaining sufficient back focus even with high zoom ratio.
2Adaptability or versatility
If the angle of view is widened to meet the demand for wide angle of view, then the field of view is improved, but the aberration correction becomes more difficult
Solution Approach 1:
The fifth lens group (G5) is specifically designed with a combination of positive and negative lenses having different Abbe numbers to address local aberration issues. The positive lenses have Abbe numbers of 50 or more, while negative lenses have Abbe numbers of 30 or less, creating local optical compensation zones that correct chromatic and spherical aberrations across the wide field of view.
Solution Approach 2:
The fifth lens group uses composite lens structures combining materials with different Abbe numbers (dispersion characteristics). This composite approach allows simultaneous correction of multiple types of aberrations (chromatic, spherical, field curvature) that become more pronounced with wide angle of view, achieving excellent image quality across the entire field.
3Illumination intensity
If multiple light bulbs are used to combine various colors, then the color reproduction is improved, but the back focus length increases
Solution Approach 1:
The optical system is designed with the prism positioned at a predetermined location within the back focus region, and the lens groups are configured to maintain the necessary back focus length from the outset. The fixed sixth lens group (G6) with positive refractive power helps control the back focus distance, ensuring there is always sufficient space for the color-combining prism regardless of the zoom setting.
4Manufacturing precision
If a complex lens structure is used to correct aberrations, then the image quality is improved, but the device complexity increases
Solution Approach 1:
The fifth lens group (G5) is designed as a multi-functional unit that simultaneously corrects multiple types of aberrations (spherical, chromatic, field curvature) through its combination of positive and negative lenses. This single lens group performs what would otherwise require multiple separate correction elements, reducing overall system complexity while maintaining excellent aberration correction across the wide angle of view and high zoom ratio.
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 provides a zoom lens with a high zoom ratio, wide angle of view, and sufficient back focus, effectively correcting spherical aberration and field curvature, while maintaining a compact design and improving image quality.
Implementation Method 1
a first lens group having a negative refractive power; a second lens group having a positive refractive power; a third lens group having a positive refractive power; a fourth lens group having a negative refractive power; a fifth lens group having a positive refractive power; and a sixth lens group having a positive refractive power
Data Source
AI summary
A zoom lens for projection includes negative first group G1, positive second group G2, positive third group G3, negative fourth group G4, positive fifth group G5, and positive sixth group G6, arranged from the magnification side of the zoom lens. The reduction side of the zoom lens is telecentric. When the magnification is changed, the first group G1 and the sixth group G6 are fixed, and the second through fifth groups G2 through G5 move. The fourth group G4 is a negative lens having a concave surface facing the magnification side, and the fifth group G5 includes at least two positive lenses and at least two negative lenses. Further, the following formula (1) is satisfied:−5.0≦f4/fw≦−1.2 (1),where f4: the focal length of the fourth group; andfw: the focal length of the entire system of the zoom lens at a wide angle end.