Zoom Lens with Segmented Focus Groups for Compact Autofocus
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Solution Overview
Problem
Existing zoom lenses face challenges in achieving a compact, high-performance design with a wide angle of view, high zoom ratio, and fast autofocus while minimizing the moving amount of focus lenses, which affects size and noise during video shooting.
Innovation Solution
A zoom lens configuration comprising a first positive refractive power lens group, a second negative refractive power lens group, a third negative meniscus lens group with a concave surface, a fourth positive refractive power lens group, and a fifth positive refractive power lens group, with specific interval adjustments and lateral magnification conditions to optimize zooming and focusing, using a third lens group with low dispersion glass for aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a second lens group with negative refractive power is used as focus lens, then the zoom lens can achieve compact total length and high zoom ratio, but the large weight of the second lens group requires a large motor/actuator, increasing the maximal diameter of lens barrel and making it difficult to heighten AF operation speed
Solution Approach 1:
The patent divides the focus lens function into multiple negative lens groups (second and third lens groups) rather than using a single heavy negative lens group. This segmentation allows each group to be optimized for specific functions, reducing the weight and size of individual focus lens components while maintaining overall compactness.
Solution Approach 2:
The patent assigns different roles to different lens groups: the second lens group is optimized for zooming with specific movement characteristics, while the third lens group is designated as the focus lens with lighter weight. This local optimization allows the focus lens to be lighter without compromising the zooming performance of the second lens group.
2Weight of moving object
If a single negative lens is used as focus lens, then the lens barrel can be downsized and high speed AF operation can be achieved, but the zooming operation needs to be improved and further downsizing is required
Solution Approach 1:
The patent combines the zooming function of the second lens group with the focusing function of the third lens group. By merging these functions into a coordinated two-group system rather than relying on a single lens group for both functions, the patent achieves both compact size and improved zooming operation performance.
Solution Approach 2:
The patent implements dynamic coordination between the second and third lens groups during zooming and focusing operations. The control mechanism adjusts the movement of both groups in a coordinated manner, allowing the lighter third lens group to serve as focus lens while maintaining excellent zooming performance through the combined action of both groups.
3Speed
If the moving amount of focus lens is reduced, then autofocus speed can be heightened and noise during video shooting can be reduced, but the lens configuration and interval adjustments become more complex
Solution Approach 1:
The patent optimizes specific parameters including the focal lengths, refractive powers, and interval changes of the lens groups to enable the third lens group to achieve focusing with minimal movement. By carefully controlling parameters such as the ratio of focal lengths and the magnitude of interval changes during zooming, the patent reduces focus lens moving amount while managing the complexity through mathematical relationships between group parameters.
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
The solution enables a compact, high-performance zoom lens with a half angle of view of 36.8 degrees or more, a zoom ratio of 2.8 to 5.0, and reduced focus lens movement, enhancing autofocus speed and reducing noise, while maintaining image quality and aberration correction.
Implementation Method 1
a third lens group having a negative refractive power and comprised of a single negative meniscus lens with a concave surface on an object side, to move along an optical axis for focusing
Implementation Method 2
when zooming from a wide angle end to a telephoto end, the zoom lens is moved so that an interval between the first and second lens groups increases, an interval between the second and third lens groups increases
Data Source
AI summary
A zoom lens includes first to fifth lens groups having positive, negative, negative, positive, and positive refractive power, respectively. The third lens group includes a single negative meniscus lens with a concave surface on an object side, to move along the optical axis for focusing. When zooming from a wide angle end to a telephoto end, an interval between the first and second lens groups increases, an interval between the second and third lens groups increases, an interval between the third and fourth lens groups decreases, and an interval between the fourth and fifth lens groups decreases. The fourth and fifth lens groups are set to have a combined lateral magnification β45T to satisfy the following condition, when an object distance is infinite at a telephoto end:−0.041<β45T/Ft<−0.025where Ft is a focal length of the entire zoom lens at the telephoto end.