Inner Focus Imaging Lens Reducing Weight and Aberration
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Solution Overview
Problem
Existing imaging lenses face challenges in achieving a balance between reducing size, weight, and aberration variation while maintaining high-speed focusing and large aperture performance, particularly in inner focus type configurations.
Innovation Solution
The imaging lens configuration includes a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, where the second lens group travels along the optical axis for focusing, and specific conditional expressions are satisfied to optimize optical performance, size reduction, and focusing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the focus lens group is arranged near the aperture stop to reduce weight, then the weight of the focus lens group is reduced, but the diameter of the first lens group must be increased to secure peripheral light amount, resulting in higher cost
Solution Approach 1:
The patent relocates the aperture stop from its conventional position between lens groups to a position adjacent to the image sensor (fourth lens group), effectively changing the spatial dimension of the optical system. This dimensional reorganization allows the first lens group to maintain a compact diameter while still achieving sufficient peripheral light collection, resolving the contradiction between weight reduction and light gathering area.
2Reliability
If the first lens group has a positive-negative-negative-positive symmetrical structure with a large air lens, then aberration correction is improved, but the total length of the lens system becomes difficult to suppress
Solution Approach 1:
The patent extracts and eliminates the large air lens from the optical system, replacing it with a compact refractive structure. This removal of the bulky air lens component directly reduces the total length of the lens system while maintaining aberration correction through optimized refractive indices and curvatures of the remaining lens elements.
Solution Approach 2:
The patent changes the material parameters (refractive indices) of the lens elements, specifically using a low-dispersion glass with a refractive index of 1.66 or higher for the first lens group. This parameter change enables effective aberration correction with a more compact lens structure, reducing total length while maintaining optical performance.
3Reliability
If an intermediate telephoto configuration is adopted to correct off-axial aberration, then off-axial aberration correction is improved, but backfocus becomes longer and size reduction becomes difficult
Solution Approach 1:
The patent inverts the conventional telephoto configuration by placing the aperture stop adjacent to the image sensor rather than in the middle of the lens system. This inversion allows the use of a compact first lens group with high refractive index glass to achieve both on-axis and off-axis aberration correction without requiring long backfocus distances, thus reducing overall system size.
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 achieves favorable optical performance, reduces size and weight, and enables high-speed focusing while maintaining a large aperture, thereby addressing the limitations of previous lens systems.
Implementation Method 1
a first lens group having positive refractive power
Implementation Method 2
a second lens group having negative refractive power, and a focusing operation is performed through allowing the second lens group to travel along an optical axis
Implementation Method 3
a third lens group having positive refractive power
Data Source
AI summary
An imaging lens includes a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. The first to third lens groups are arranged in order from an object side toward an image side. A focusing operation is performed through allowing the second lens group to travel along an optical axis. The following conditional expressions are satisfied,0.40<Da/TL<0.65 (1)0.90<f3/f<3.50 (2)where Da is an on-axial distance from an object-sided surface of the second lens group to an image-sided surface of the third lens group in an infinite focus state, TL is an on-axial total length of the imaging lens, f3 is a focal length of the third lens group, and f is a total focal length of the imaging lens in the infinite focus state.