Zoom Lens Refractive Power Distribution for Compact Autofocus
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Solution Overview
Problem
Existing zoom lenses face challenges in achieving a wide angle of view, small size, high-speed autofocusing, and minimal aberration variations while maintaining high optical performance, particularly in image pickup apparatuses like digital cameras, due to the trade-offs between lens unit configuration, refractive powers, and movement amounts.
Innovation Solution
A zoom lens configuration with specific refractive power distributions and movement patterns, including a first lens unit with negative power, a second with positive power, a third with negative power, and a fourth with negative power, where the third lens unit moves during focusing and the rear lens group has positive power over the entire zoom range, satisfying conditional expressions to optimize focal lengths and movement amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If the number of constituent lenses of the focus lens unit is reduced to make it smaller in size and weight, then the lens unit becomes more compact and lighter, but residual aberrations increase and aberration variations during focusing become larger
Solution Approach 1:
The patent changes the refractive power distribution parameter by setting the absolute value of the refractive power of the focus lens unit to be 0.05 times or more but 0.30 times or less of the focal length of the zoom lens. This parameter optimization allows the focus lens unit to achieve effective focusing with reduced constituent lenses while controlling aberration variations within acceptable ranges.
Solution Approach 2:
The patent applies local quality by assigning different refractive power characteristics to different lens units. Specifically, the focus lens unit is designed with a particular refractive power range relative to the overall zoom lens, while other lens units have different refractive power characteristics. This localized optimization of refractive power distribution enables the focus lens unit to maintain compact size with controlled aberrations.
2Manufacturing precision
If the power of the focus lens unit is reduced to decrease aberration variations during focusing, then aberration control improves, but the movement amount during focusing increases and the total length of the zoom lens increases
Solution Approach 1:
The patent optimizes the refractive power parameter of the focus lens unit to a specific range (0.05-0.30 times the focal length of the zoom lens) that balances two competing requirements: keeping aberration variations small while limiting the movement amount during focusing. This parameter optimization prevents the focus lens unit from needing to move excessively long distances while still maintaining good aberration control.
3Volume of moving object
If a zoom lens with wide angle of view and small size is designed, then the system becomes more compact and has wider viewing capability, but it becomes difficult to achieve high-speed autofocusing with minimal drive sound
Solution Approach 1:
The patent optimizes the refractive power parameter of the focus lens unit to enable high-speed focusing within a compact form factor. By setting the refractive power to 0.05-0.30 times the focal length of the zoom lens, the design achieves a balance where the focus lens unit can move sufficiently fast for high-speed autofocusing while the overall lens system remains compact for wide angle of view and small size requirements.
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, high-performance zoom lens with reduced aberration variations and improved focusing speed, achieving a balance between lens size, weight, and optical performance across the entire zoom range.
Implementation Method 1
the third lens unit is configured to move in an optical axis direction during focusing
Data Source
AI summary
Provided is a zoom lens, including, in order from an object side to an image side: a first lens unit to a fourth lens unit having negative, positive, negative, and negative refractive powers; and a rear lens group. In the zoom lens, an interval between each pair of adjacent lens units is changed during zooming, the rear lens group has a positive refractive power over an entire zoom range, the third lens unit is configured to move in an optical axis direction during focusing, and each of a focal length of the zoom lens at a wide angle end (fw), and a focal length of the third lens unit (f3) is appropriately set.