Zoom Lens Inner Focus Aberration Control
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Solution Overview
Problem
Existing zoom lenses using the inner focus system face challenges in achieving high optical characteristics over an entire object distance while maintaining a high zoom ratio and downsizing the lens system, as they tend to generate larger aberration variations, particularly at close distances.
Innovation Solution
A zoom lens configuration with a first lens unit having positive refractive power, a second lens unit with negative refractive power, and a rear unit with multiple lens units of positive refractive power, where the interval between adjacent lens units changes during zooming, and the focus unit moves during focusing, adhering to specific conditional expressions to minimize aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the inner focus system is used with multiple lens units moved during zooming, then the beam effective diameter of the first lens unit is reduced and the lens system is downsized, but the aberration variations increase particularly at close distances
Solution Approach 1:
The zoom lens is divided into multiple lens units (first lens unit L1, second lens unit L2, third lens unit L3, fourth lens unit L4, fifth lens unit L5) with different functions. The first lens unit handles focusing, while the second through fifth lens units handle zooming. This segmentation allows each unit to be optimized for its specific function, reducing overall aberration variations while maintaining compact size.
Solution Approach 2:
Different lens units are assigned different refractive powers and movement characteristics tailored to their specific functions. The first lens unit has positive refractive power for focusing, while the second has negative refractive power for zooming. This localized optimization of optical properties minimizes aberration variations at close distances while maintaining the downsized structure.
2Reliability
If the first lens unit is moved for focusing (front lens focus system), then the optical characteristic is maintained, but the beam effective diameter increases and the lens system becomes larger
Solution Approach 1:
The focusing function is separated from the first lens unit and assigned to a dedicated focus unit (fourth lens unit L4) within the inner focus system. This allows the first lens unit to maintain a smaller beam effective diameter while the focus unit handles the focusing operation, preserving optical characteristics without increasing overall system size.
Solution Approach 2:
The fourth lens unit acts as an intermediary focus unit that performs focusing operations without requiring the first lens unit to move. This intermediary structure enables inner focus operation with maintained optical characteristics and reduced system size compared to front lens focus systems.
3Speed
If a lens unit is moved for focusing in the inner focus system, then the focusing speed increases, but the refractive power configuration becomes critical and complex
Solution Approach 1:
The fourth lens unit is specifically configured with positive refractive power and designated as the focus unit, while other lens units have different refractive powers optimized for zooming. This localized assignment of optical properties simplifies the overall configuration by clearly defining which unit performs which function, reducing the complexity of refractive power management while enabling fast focusing.
Solution Approach 2:
The refractive powers of the lens units are specifically optimized to satisfy certain conditional expressions, ensuring that the focus unit (fourth lens unit) can move efficiently for focusing while maintaining optical performance. This parameter optimization enables fast focusing without excessive complexity in the overall configuration.
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 achieves high optical characteristics over the entire zoom range and object distance, reducing aberration variations, especially at the telephoto end, while enabling fast and precise focusing.
Implementation Method 1
a first lens unit L1 having a positive refractive power; a second lens unit L2 having a negative refractive power; and a rear unit LB including a plurality of lens units and having a positive refractive power as a whole
Data Source
AI summary
Provided is a zoom lens, including, in order from an object side to an image side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; and a rear unit including a plurality of lens units and having a positive refractive power as a whole, in which an interval between adjacent lens units is changed during zooming. The rear unit includes a focus unit having a positive refractive power, which is configured to move during focusing. An optical system arranged on the image side of the focus unit has a negative refractive power at a telephoto end. A focal length (ft) of the zoom lens at the telephoto end and a combined focal length (fpt) of an optical system arranged on the object side of the focus unit are each appropriately set.