Zoom Lens with Intermediate Cemented Group for Compact High-Aperture Design
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Solution Overview
Problem
Current zoom lenses with large aperture ratios face challenges in achieving both high optical performance and miniaturization, as well as optimal focus group placement for smooth image magnification during live view and tracking AF, leading to discomfort and difficulty in quick focusing.
Innovation Solution
A zoom lens configuration comprising a first positive refractive power group, a second negative refractive power group, an intermediate group with cemented diverging surfaces, and a rear negative refractive power group, where the intermediate group includes at least two cemented diverging surfaces, and the lens group F moves on the optical axis for focusing, satisfying specific conditional expressions for refractive power and F value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a lens group with strong positive refractive power is disposed at the rear of the entire system to achieve a small F value, then the aperture ratio is improved, but the overall optical length increases and telephoto tendency is reduced
Solution Approach 1:
The optical system is divided into five distinct lens groups (G1-G5) with alternating positive and negative refractive powers. The intermediate group M is further segmented into multiple lens elements including cemented lenses. This segmentation allows distribution of refractive power across multiple groups, enabling strong positive power in the intermediate group without requiring a strong positive group at the rear, thus maintaining compact length while achieving small F value.
Solution Approach 2:
Different regions of the optical system are assigned different refractive power characteristics. The intermediate group M is given strong positive refractive power with specific local quality through cemented diverging surfaces, while the rear group R is designed with negative refractive power to provide telephoto tendency. This local differentiation allows the system to achieve small F value through the intermediate group while the rear group compensates to maintain compact overall length.
2Ease of operation
If the focus group is disposed on the object side of the optical system to enable contrast AF and tracking AF, then live view imaging is improved, but the change in image magnification increases causing discomfort
Solution Approach 1:
The patent changes the positional parameter of the focus group from the object side to the image side of the optical system. This parameter change fundamentally alters the magnification characteristics during focusing operation. By placing the focus group (G5) on the image side with negative refractive power, the system achieves minimal image magnification change during focus adjustment, eliminating the discomfort associated with large magnification variations while still supporting contrast AF and tracking AF functions.
3Adaptability or versatility
If the second lens group with strong negative refractive power is used in a positive-lead type configuration to achieve high variable magnification, then zoom capability is improved, but the telephoto tendency becomes too strong making it difficult to shorten overall length
Solution Approach 1:
The patent inverts the conventional positive-lead configuration by making the first lens group G1 have positive refractive power instead of negative. This inversion changes the telephoto tendency characteristics of the system. Combined with the intermediate group M having strong positive power and the rear group R having negative power, this inversion allows achieving high variable magnification ratio without excessive telephoto tendency, enabling compact overall length while maintaining zoom capability.
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 results in a compact zoom lens with excellent optical performance and a large aperture ratio, reducing image magnification variation and enabling high-speed autofocus, suitable for live view and tracking AF applications.
Implementation Method 1
the intermediate group M includes at least two lens surfaces Si each of which is a cemented surface and is a diverging surface
Implementation Method 2
the lens group F moves on an optical axis in focusing
Data Source
AI summary
Provided are: a zoom lens including, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, an Intermediate group having one or more lens groups and having positive refractive power as a whole, a lens group having negative refractive power, and a rear group having one or more lens groups, wherein the intermediate group includes at least two lens surfaces each of which is a cemented surface and is a diverging surface, a space between adjacent lens groups changes in zooming, the lens group moves on an optical axis in focusing, and the zoom lens satisfies the predetermined conditional expression; and an imaging apparatus including the zoom lens.