Inner-Focus Lens System Aberration Control
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Solution Overview
Problem
Existing inner-focus large-aperture medium-telephoto lens systems face challenges in achieving lightweight focusing while maintaining satisfactory imaging performance and proper residual spherical aberration, particularly in reducing off-axial aberrations and front lens diameter.
Innovation Solution
The system consists of a first and third lens group with positive refractive power, and a second lens group that moves toward the object side, comprising a single negative lens element and at least two positive lens elements, with specific curvature and focal length ratios to optimize aberration correction and weight, including a cemented lens element for controlled spherical aberration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the second lens group has a negative refractive power to reduce focusing weight, then the focusing group becomes lightweight, but the front lens diameter increases and off-axial aberrations vary greatly during focusing
Solution Approach 1:
The patent applies parameter changes by carefully controlling the refractive powers and focal lengths of lens elements within the second lens group. Specifically, it sets the focal length of the second lens group (f2) relative to the entire system (f) within 0.3<f2/f<0.7, and configures the lens elements with specific refractive powers to achieve both weight reduction and aberration control without increasing front lens diameter
2Weight of moving object
If the second lens group has a negative refractive power to reduce focusing weight, then the focusing group becomes lightweight, but focusing-induced variation in off-axial aberrations increases
Solution Approach 1:
The patent controls off-axial aberration variation through precise parameter setting of lens elements. It specifies that the second lens group should include lens elements with particular refractive powers and focal lengths, and positions the aperture stop at specific locations, to minimize the variation of off-axial aberrations during focusing while maintaining lightweight construction
Solution Approach 2:
The patent introduces an aperture stop as an intermediary element within the second lens group. By strategically positioning the aperture stop, it mediates the ray paths and reduces the variation of off-axial aberrations during focusing, allowing the negative-powered second lens group to remain lightweight without sacrificing aberration control
3Manufacturing precision
If the second lens group has a positive refractive power with multiple lens elements to reduce off-axial aberrations, then aberration control improves, but the focusing group weight increases
Solution Approach 1:
The patent achieves lightweight construction with good aberration control by optimizing the parameters of lens elements in the second lens group. It specifies particular ranges for focal lengths and refractive powers, and carefully selects the number and arrangement of lens elements, to minimize weight while maintaining adequate off-axial aberration control
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
This configuration results in a lightweight focusing group with desired residual spherical aberration and optical performance from infinity to close distances, enabling compact, high-performance digital appliances with minimal size increase.
Implementation Method 1
a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group in order from the object side
Data Source
AI summary
The disclosed internal focusing large-aperture medium telephoto lens has as lens groups a positive first lens group, a positive second lens group, and a third lens group, in that order from the object side. When focusing on nearby objects, the first lens group and the third lens group have a fixed position relative to the image surface, and the second lens group displaces toward the object side. The second lens group has only one negative lens, and, in order from the object side, has at least a positive lens, a negative lens, and a positive lens. The following expression is fulfilled: −0.5<(R1+R2)(R1−R2)<−0.1 (wherein, R1: radius of curvature of the object side surface of the negative lens in the second lens group; R2: radius of curvature of the image side surface of the negative lens in the second lens group).