Inner Focus Lens Compactness and Stabilization via Inverted Third Group
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Solution Overview
Problem
Conventional inner focus lenses struggle to achieve compact size and high imaging performance, especially for video filming, due to limitations in diameter reduction and stabilization correction, and fail to accommodate wide angle views effectively.
Innovation Solution
The inner focus lens configuration includes a first positive lens group, a second negative lens group moved along the optical axis for focusing, and a third negative lens group with a sub-lens configuration to reduce diameter and enhance telecentricity, satisfying specific conditional expressions for stabilization correction and focal length ratios to achieve compactness and high imaging performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a positive lens element is disposed farthest on the image side to assure telecentricity, then imaging performance is improved, but the diameter of the third lens group cannot be sufficiently reduced
Solution Approach 1:
The patent inverts the conventional arrangement by placing a negative lens element farthest on the image side instead of a positive lens element. This reversal allows the third lens group diameter to be reduced while still achieving acceptable imaging performance through alternative optical design approaches.
Solution Approach 2:
The patent changes the refractive power parameter of the third lens group from positive to negative, which fundamentally alters the optical path and allows for diameter reduction. This parameter change enables the lens group to function differently, achieving compactness while maintaining imaging capabilities through the overall optical system design.
2Area of stationary object
If the third lens group diameter is reduced for compactness, then device size is reduced, but stabilization correction performance deteriorates
Solution Approach 1:
The patent employs asymmetric lens element configurations within the third lens group, where lens elements have different shapes, sizes, and positions. This asymmetry allows for optimized light path control that maintains stabilization correction performance despite the reduced overall diameter of the lens group.
Solution Approach 2:
The patent addresses the stabilization correction challenge by optimizing the axial (depth) dimension rather than relying solely on lateral diameter. Through careful control of lens element positions along the optical axis and their curvature radii, the patent achieves effective stabilization correction within a compact radial footprint.
3Area of stationary object
If a negative lens element is disposed farthest on the image side to reduce diameter, then compactness is improved, but telecentricity and light incidence quality deteriorate
Solution Approach 1:
The patent uses the second lens group (focusing group) as an intermediary to compensate for the oblique light incidence caused by the negative lens element at the image side. By coordinating the movement and positioning of the second lens group, the system maintains adequate light incidence quality on the image sensor despite the unconventional negative lens termination.
Solution Approach 2:
The second lens group serves multiple functions: it acts as the focusing group for autofocus operations, compensates for light incidence angles caused by the terminal negative lens, and contributes to overall aberration correction. This multi-functionality allows the system to achieve compactness without sacrificing light incidence quality.
4Productivity
If the focusing group is made small and light-weight for rapid wobble, then video filming performance is improved, but focusing precision may deteriorate
Solution Approach 1:
The patent merges the stabilization function and focusing function into a coordinated system. The third lens group provides stabilization correction while the second lens group performs focusing, with both groups working in concert. This merging allows the compact focusing group to achieve both rapid autofocus response and adequate focusing precision through the combined optical effects of multiple lens groups.
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 enables a compact inner focus lens with improved stabilization correction performance, reduced size and weight, and high imaging quality suitable for video filming, while accommodating wide angles and standard angles of view, facilitating size reductions in optical systems.
Implementation Method 1
a second lens group having a negative refractive power; and the second lens group is moved along an optical axis, whereby focusing from a focus state for an object at infinity to a focus state for a minimum object distance is performed
Implementation Method 2
A lens group configured by a lens other than a lens that is disposed farthest on the object side is moved in a direction orthogonal to the optical axis to shift an image
Data Source
AI summary
An inner focus lens includes sequentially from an object side, a first lens group having a positive refractive power; a second lens group having a negative refractive power; and a third lens group having a negative refractive power. The second lens group is moved along an optical axis, whereby focusing from a focus state for an object at infinity to a focus state for a minimum object distance is performed. A lens group configured by a lens other than a lens that is disposed farthest on the object side is moved in a direction orthogonal to the optical axis to shift an image. The inner focus lens satisfies a conditional expression (1) 0.15≦(1−βp)×βr≦4.50, where βp is transverse magnification of the orthogonally moved lens group and βr is composite transverse magnification of a lens group disposed farther on an image side than the orthogonally moved lens group.