Zoom Lens with Cemented Diffraction Element for Chromatic Aberration Control
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Solution Overview
Problem
Existing zoom lenses face challenges in achieving both compactness and high performance, particularly in the super-telephoto area, while maintaining good image forming performance and minimizing issues like color shifting and flares.
Innovation Solution
A zoom lens configuration with three lens groups of positive, negative, and positive refractive power, incorporating a diffraction optical element with a refractive index difference of 0.45 or less, and a diffraction optical surface with diffraction grating grooves, satisfying specific conditional expressions for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional zoom lens designs are used, then basic zoom functionality is achieved, but image forming performance deteriorates in the super-telephoto area with increased color shifting and flares
Solution Approach 1:
The patent applies parameter changes by carefully selecting and controlling the refractive index difference between optical materials in the diffraction optical element, specifying that the refractive index difference at the d-line should be 0.45 or less. This parameter optimization enables effective chromatic aberration correction while maintaining good image forming performance in the super-telephoto area, directly addressing the color shifting issue.
Solution Approach 2:
The patent employs composite materials by combining optical elements with different refractive index characteristics in a cemented configuration within the diffraction optical element. This composite structure allows the system to leverage the complementary optical properties of different materials to correct chromatic aberrations and reduce flares, thereby improving overall image forming performance.
2Reliability
If zoom lens complexity is increased to improve image forming performance, then chromatic aberration correction improves, but device size increases
Solution Approach 1:
The patent merges multiple functions into a single diffraction optical element by combining chromatic aberration correction and diffraction-based focusing capabilities in one component. The cemented optical elements with controlled refractive index differences are integrated into a unified structure that performs multiple optical corrections simultaneously, avoiding the need for separate correction lenses and thereby controlling overall lens size.
Solution Approach 2:
The patent uses parameter changes by optimizing the refractive index difference to be 0.45 or less, which enables effective chromatic aberration correction with a more compact element design. This parameter optimization allows the diffraction optical element to achieve high correction performance without requiring increased element size or additional lens groups.
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 and high-performance zoom lens that achieves excellent image forming performance in the super-telephoto area, effectively correcting chromatic aberrations and minimizing flares, thereby enhancing image quality.
Implementation Method 1
a diffraction optical element in which two optical elements, constituted by optical materials of which refractive index difference at the d-line is 0.45 or less, are cemented, and a diffraction optical surface on which diffraction grating grooves are formed exists on the interface of the two optical elements
Data Source
AI summary
Provided is a zoom lens having, in order from an object: a first lens group (G1) having positive refractive power; a second lens group (G2) having negative refractive power; and a third lens group (G3) having positive refractive power. The first lens group (G1) and the third lens group (G3) respectively move toward the object upon zooming from the wide-angle end state to the telephoto end state. The first lens group (G1) includes a diffraction optical element (DOE) in which two optical elements, constituted by optical materials of which refractive index difference at the d-line is 0.45 or less, are cemented and a diffraction optical surface (corresponding to the optical surface with the radius of curvature R8 in FIG. 1) on which diffraction grating grooves are formed, exists on the interface of the two optical elements. The zoom lens satisfies the following conditional expressions: 0.05<φ1/ft<1.00, and 3.0<φd/y<10.0, where φ1 denotes an effective diameter of a surface closest to the object in the first lens group (G1), ft denotes a focal length of the zoom lens (ZL) in the telephoto end state, φd denotes an effective diameter of the diffraction optical surface, and y denotes a maximum image height of the zoom lens (ZL).