Zoom Lens Four-Group Configuration for Constant F-Number
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Solution Overview
Problem
Existing zoom lenses for electronic cameras, particularly those used in broadcasting and movie production, face challenges in maintaining a constant F-number during magnification changes, achieving a compact and lightweight design, and correcting aberrations effectively while supporting high-definition imaging.
Innovation Solution
A zoom lens configuration comprising a first lens group with positive refractive power fixed during magnification, a second lens group with negative refractive power moving from the object side to the image side, a third lens group with negative refractive power that corrects image plane movement, and a fourth lens group with positive refractive power including a stop, where the distance between the second lens groups changes, and the third lens group moves to provide a wide movement range, ensuring a constant F-number and reduced aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the first lens group size is reduced to achieve a compact and lightweight design, then the lens weight and size are reduced, but the F-number becomes non-constant during magnification change
Solution Approach 1:
The lens system is divided into four distinct lens groups with specific refractive power assignments. The first lens group (positive refractive power) is fixed during magnification change, while the second lens group (negative refractive power) moves from object side toward image side. This segmentation allows independent optimization of each group's function, enabling constant F-number while reducing overall lens size and weight.
Solution Approach 2:
The second lens group is designed to move dynamically from the object side toward the image side during magnification change from wide angle to telephoto end. This dynamic movement enables the lens system to maintain constant F-number across different magnification levels while keeping the overall lens structure compact and lightweight.
2Weight of moving object
If the lens structure is simplified to reduce weight and size, then the lens becomes more portable, but aberration correction performance deteriorates
Solution Approach 1:
Each lens group is assigned specific local functions: the first lens group (positive refractive power) handles light entry and initial focusing, the second lens group (negative refractive power) manages magnification change and F-number constantness, the third lens group (negative refractive power) corrects image plane movement and aberrations, and the fourth lens group (positive refractive power) includes the stop and provides final image formation. This local quality assignment enables effective aberration correction in a compact structure.
Solution Approach 2:
The lens system employs a composite structure of four lens groups with different refractive power characteristics. By combining positive and negative refractive power groups in specific arrangements, the lens achieves both weight reduction and effective aberration correction, satisfying the requirements for portable high-performance imaging.
3Object-affected harmful factors
If the third lens group moves with a wide movement range to correct image plane movement, then aberration correction is improved, but the lens structure becomes more complex
Solution Approach 1:
The lens system is segmented into four functional groups where the third lens group (negative refractive power) is specifically assigned to correct image plane movement and aberrations. This segmentation allows the third group to have a wide movement range for effective correction while the overall structure remains organized and manageable through clear functional division.
Solution Approach 2:
The third lens group acts as an intermediary element between the second lens group (which performs magnification change) and the fourth lens group (which includes the stop). This intermediary position enables the third group to correct image plane movement and aberrations effectively while maintaining a relatively simple overall structure through its mediating role.
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 allows for a constant F-number during magnification changes, reduces the lens weight and size, and effectively corrects aberrations, enabling high-quality imaging with a compact and lightweight design suitable for portable applications.
Implementation Method 1
a first lens group having positive refractive power, and which is fixed during magnification change
Implementation Method 2
a second lens group having negative refractive power, and which moves from an object side toward an image side while magnification is changed
Implementation Method 3
a third lens group having negative refractive power, and which corrects movement of an image plane during magnification change
Implementation Method 4
a fourth lens group having positive refractive power, and which is fixed during magnification change and includes a stop
Data Source
AI summary
A zoom-lens consists of a positive-first-lens-group, fixed during magnification-change, a negative-second-lens-group, which moves from object-side toward image-side during magnification change from wide-angle-end to telephoto-end, a negative-third-lens-group, which corrects movement of an image-plane during magnification-change, and a positive-fourth-lens-group, which is fixed during magnification-change and includes a stop, in this order from object-side. The first-lens-group consists of a negative-1a-th-lens-group, fixed during focusing, a positive-1b-th-lens-group, which moves during focusing, and a positive-1c-th-lens-group, fixed during focusing, in this order from object-side. The second-lens-group consists of a negative-2a-th-lens-group and a positive-2b-th-lens-group, and a distance therebetween is changed during magnification-change. The third-lens-group moves in such a manner that a distance from the fourth-lens-group at telephoto-end is narrower than a distance from the fourth-lens-group at wide-angle-end. Predetermined conditional-formulas about a length from a most-object-side surface in the first-lens-group to the stop, a focal-length at wide-angle-end and a focal-length of the 1b-th-lens-group are satisfied.