Zoom Lens Configuration for High Zoom Ratio and Compact Length
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Solution Overview
Problem
Existing zoom lenses for image pickup apparatuses face challenges in achieving high zoom ratios, high optical performance over the entire zoom range, and a short total lens length, with difficulties in focusing due to limited space for lens movement and high refractive powers of certain lens units.
Innovation Solution
A zoom lens configuration comprising multiple lens units with specific refractive powers, where the first lens unit moves towards the object side during zooming, and the N minus second lens unit moves during focusing, with conditional expressions to optimize lens length, backfocus, and refractive power distribution, allowing for a high zoom ratio and reduced lens diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the distance between the fourth lens unit and the fifth lens unit at telephoto end is short, then the total lens length is shortened, but the space for moving the fourth lens unit during focusing becomes insufficient
Solution Approach 1:
The zoom lens is divided into multiple lens units (first through sixth lens units) with different functions. The fourth lens unit is designated specifically for focusing operations, while other lens units handle zooming and image formation. This segmentation allows the fourth lens unit to be optimized for focusing movement without compromising overall lens length.
Solution Approach 2:
The lens units are designed with dynamic movement capabilities during focusing. Specifically, the fourth lens unit moves during focusing to adjust focus from infinity to close distances, while maintaining a compact configuration at the telephoto end. This dynamic design enables sufficient focusing range within a short total lens length.
2Adaptability or versatility
If both the last lens unit and the lens unit next to it have high refractive powers, then the zoom ratio is increased, but the optical performance deteriorates
Solution Approach 1:
Different lens units are assigned different refractive power characteristics based on their specific functions. The fourth lens unit has a relatively low refractive power optimized for focusing, while other lens units have refractive powers optimized for their respective roles in zooming and image formation. This local optimization of refractive power distribution maintains high optical performance across the entire zoom range.
Solution Approach 2:
The refractive powers of individual lens units are carefully controlled within specific ranges. The fourth lens unit's refractive power is constrained to provide adequate focusing capability without excessive strength, while maintaining overall high zoom ratio. This parameter control ensures balanced optical performance throughout the zoom range.
3Ease of operation
If the backfocus is long, then the focusing capability is improved, but the total lens length increases
Solution Approach 1:
The focusing function is segmented to the fourth lens unit, which is positioned to provide adequate backfocus space specifically for focusing operations. This segmentation allows the backfocus to be optimized for focusing capability without unnecessarily increasing the overall lens length, as other lens units are configured to minimize total length.
Solution Approach 2:
The lens units are arranged in a multi-dimensional configuration along the optical axis, with the fourth lens unit positioned to provide necessary backfocus space. This spatial arrangement in the optical axis dimension enables adequate focusing capability while maintaining compact overall lens length through optimized positioning of all lens units.
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 high zoom ratio with high optical performance and a short total lens length, facilitating quick focusing and reducing mechanical complexity, while maintaining high image quality across the zoom range.
Implementation Method 1
a first lens unit having a positive refractive power, a second lens unit having a negative refractive power
Implementation Method 2
an N minus second lens unit having a negative refractive power, and an Nth lens unit having a positive refractive power
Data Source
AI summary
A zoom lens includes, in order from an object side to an image side, a positive first lens unit, a negative second lens unit, a middle lens group including at least one lens unit, a negative N minus second lens unit, a negative N minus first lens unit, and a positive Nth lens unit, where N is an integer of six or more, in which distances between the adjacent lens units change during zooming, the first lens unit moves toward the object side during zooming from a wide-angle end to a telephoto end, the N minus second lens unit moves during focusing, and a total lens length at the wide-angle end, a backfocus at the wide-angle end, and a lateral magnification of a combined system of the N minus first lens unit and the Nth lens unit at the wide-angle end are set appropriately.