Zoom Lens Fourth-B Group Inversion for Compact Back Focus
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Solution Overview
Problem
Conventional zoom lenses with a four-group configuration require a large space between lens groups, limiting miniaturization and resulting in insufficient back focus at the wide angle end, especially when used in single-lens reflex cameras, and have a relatively low zoom ratio of approximately 10.
Innovation Solution
A zoom lens configuration comprising a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive and negative refractive powers, where only the fourth-b lens group moves toward the image side during focusing, allowing for a more compact design and longer back focus while achieving a high zoom ratio exceeding 12.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fourth-b lens group is moved toward the object side for focusing, then focusing from infinity to close distance is achieved, but a large space is required between the fourth-a lens group and the fourth-b lens group, preventing miniaturization
Solution Approach 1:
The patent inverts the conventional focusing direction by moving the fourth-b lens group toward the image side instead of the object side. This reversal allows the lens group to achieve focusing from infinity to close distance while reducing the space requirement between the fourth-a and fourth-b lens groups, enabling miniaturization of the optical system.
2Reliability
If the fourth-b lens group is moved toward the object side for focusing, then focusing is achieved, but back focus at the wide angle end becomes short, preventing space for mirrors and filters in single-lens reflex cameras
Solution Approach 1:
By reversing the focusing direction to move the fourth-b lens group toward the image side, the patent achieves focusing functionality while simultaneously extending the back focus length at the wide angle end, thereby providing sufficient space for mirrors and filters in single-lens reflex camera applications.
3Reliability
If conventional four group configuration is used, then focusing functionality is achieved, but zoom ratio is limited to approximately 10, which is not sufficiently high
Solution Approach 1:
The patent implements dynamic movement of multiple lens groups including the first, second, third, and fourth lens groups to achieve zooming, while the fourth-b lens group dynamically moves for focusing. This dynamic configuration enables a zoom ratio exceeding 12 while maintaining full focusing functionality across the zoom range.
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 the miniaturization of the optical system, secures space for camera components like mirrors and filters, and maintains appropriate image movement sensitivity, achieving high-performance zoom lenses with a small size and long back focus.
Implementation Method 1
a fourth-b lens group having negative refractive power... only the fourth-b lens group is moved toward the image side while focusing from an infinity to a close distance
Data Source
AI summary
A zoom lens substantially consists of a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group in this order from the object side, wherein the distance between the first lens group and the second lens group increases and the distance between the second lens group and the third lens group decreases, and the distance between the third lens group and the fourth lens group decreases while changing magnification. The fourth lens group substantially consists of a positive fourth-a lens group composed of a biconvex-shape lens, a negative meniscus-shape lens, and a biconvex-shape lens and a negative fourth-b lens group composed of a positive meniscus-shape lens and a biconcave-shape lens in this order from the object side, and only the fourth-b lens group is moved toward the image side while focusing.