Negative-Positive-Negative Lens Group Configuration for Compact Macro Photography
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Solution Overview
Problem
Existing macro lenses face challenges in achieving a small moving amount during close-range photography while maintaining effective aberration correction, particularly due to large moving amounts of lens groups, which complicates the design of interchangeable lens systems and makes it difficult to control spherical aberration and curvature of field.
Innovation Solution
The design of an imaging lens comprising a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with negative refractive power, where at least one of the first and second lens groups move to vary the distance between them, satisfying specific conditional expressions to optimize focal lengths and moving amounts, thereby reducing the overall lens barrel length and correcting aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a large moving amount of lens groups is used for close-range photography, then shooting magnification can be increased, but the lens barrel length becomes excessively long and the structure becomes complex
Solution Approach 1:
The patent employs dynamic focusing by moving at least one lens group (G1 or G2) along the optical axis to vary object distance and achieve different shooting magnifications. This dynamic adjustment allows the lens to adapt from infinity focusing to close-range macro photography without requiring a fixed long barrel structure, resolving the contradiction between adaptability and compactness
Solution Approach 2:
The lens is divided into multiple independent lens groups (G1, G2, G3) with different refractive powers, where G1 has negative power, G2 has positive power, and G3 has negative power. This segmentation allows selective movement of specific groups to achieve focusing and magnification changes while keeping the overall structure more compact than a single-group design would require
2Length of stationary object
If the moving amount of the first lens group is reduced to downsize the lens, then spherical aberration and curvature of field variations become difficult to control
Solution Approach 1:
Different lens groups are assigned different refractive powers and movement characteristics: G1 (negative power) and G2 (positive power) can move for focusing while G3 (negative power) remains fixed. This local differentiation of optical properties and movement behavior allows compact sizing with reduced moving amounts while maintaining aberration correction through the complementary roles of each lens group
Solution Approach 2:
The patent changes the optical parameters by using a specific configuration of negative-positive-negative refractive power distribution across three lens groups. This parameter configuration, combined with controlled movement of G1 and G2, enables maintaining aberration correction reliability even with reduced moving amounts compared to conventional designs
3Adaptability or versatility
If the distance between lens groups is varied for focusing, then close-range photography capability is improved, but the lens barrel structure becomes more complex
Solution Approach 1:
The lens barrel structure is designed to dynamically adjust the distances between lens groups during focusing operations. At least one lens group (G1 or G2) moves along the optical axis to vary object distance, enabling the system to adapt from infinity focusing to close-range photography while maintaining a relatively simple barrel structure through controlled mechanical movement
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 downsized imaging lens with a small moving amount and well-corrected aberrations, suitable for applications like single-lens reflex cameras, achieving a shooting magnification of 0.5 or higher with improved optical performance across various focusing ranges.
Implementation Method 1
an imaging lens including, in order from an object side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power
Data Source
AI summary
An imaging lens SL mounted in a single lens reflex digital camera 1 is composed of, in order from an object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having negative refractive power. Upon focusing on a near-distance object from an infinitely distant object, a configuration is that at least any one of the first lens group G1 and the second lens group G2 is moved to the object side to vary a distance between the first lens group G1 and the second lens group G2. Accordingly, a downsized imaging lens having a small moving amount upon shooting a close range object, in which various aberrations are well corrected is provided.