Zoom Lens Aspherical Front Unit Aberration Correction
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Solution Overview
Problem
Existing zoom lenses with wide angles face challenges in correcting offaxial aberrations such as distortion, field curvature, and astigmatism due to large entrance heights of offaxial light rays, which are exacerbated by the need for a reduced front lens effective aperture to maintain compactness and high optical performance.
Innovation Solution
A zoom lens configuration featuring a front unit with a negative refractive power lens having an aspherical shape, where the positive refractive power increases towards the edge, combined with a rear unit including an aperture stop and multiple lens units, allowing for adjustable intervals between lens units during zooming to manage aberrations and maintain a small front lens effective aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the refractive power of the first lens unit is increased to decrease the front lens effective aperture, then the compactness is improved, but offaxial aberrations increase
Solution Approach 1:
The patent applies an aspherical surface to the negative lens in the first lens unit. The aspherical shape allows the lens to correct offaxial aberrations (distortion, field curvature, astigmatism) while maintaining the increased refractive power needed for compactness. The specific aspherical profile compensates for the aberrations introduced by the high refractive power configuration.
Solution Approach 2:
The patent introduces a positive lens with specific refractive index and Abbe number characteristics into the first lens unit. This local optimization of lens material properties allows the system to maintain compactness while controlling offaxial aberrations through the combined effect of the positive and negative lenses.
2Adaptability or versatility
If a negative lead type zoom lens with retrofocus type arrangement is adopted to widen the angle of field, then the angle of field is improved, but offaxial aberrations increase at wide angle end
Solution Approach 1:
The aspherical surface on the negative lens corrects the offaxial aberrations (distortion, field curvature, astigmatism) that are inherently increased by the retrofocus type arrangement at wide angle. The aspherical profile provides the necessary correction while maintaining the wide angle capability.
Solution Approach 2:
The patent specifies particular ranges for the refractive index (1.80-2.00) and Abbe number (35-55) of the positive lens, and the focal length ratio (0.40-0.70) to optimize the balance between wide angle performance and aberration correction.
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 effectively corrects various aberrations across the wide angle range, achieving a high image formation performance with a wide angle of field exceeding 100° and a small front lens effective aperture, while maintaining a compact design.
Implementation Method 1
a lens surface of the negative lens G11 on the image side has an aspherical shape by which the positive refractive power increases from a center to an edge
Data Source
AI summary
A zoom lens includes a front unit including one lens unit having a negative refractive power, and a rear unit including an aperture stop and one or more lens units and having a positive refractive power as a whole, and an interval between adjacent lens units changes during zooming such that an interval between the front unit and rear unit decreases at a telephoto end when compared to a wide angle end. The front unit includes a negative lens G11 in a position closest to the object side, and a lens surface of the negative lens G11 on the image side has an aspherical shape by which the positive refractive power increases from a center to an edge. Various parameters for the zoom lens according to the present invention are properly set.