Imaging Lens with Antireflection Coating for Back Focus
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Solution Overview
Problem
Macro lenses face challenges in maintaining sufficient back focus while reducing total lens length and moving amount, and in minimizing ghost images and flare, particularly due to the negative refractive power of the third lens group causing image plane deviation and requiring complex lens barrel mechanisms.
Innovation Solution
The configuration includes a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with negative refractive power, where the first and second lens groups move together with a varying distance between them upon focusing, and at least one optical surface is coated with an antireflection coating using a wet process to reduce reflections and simplify the lens barrel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the third lens group has negative refractive power to downsize the overall length, then the total lens length is reduced, but the image plane deviates in the object-sided direction and sufficient back focus cannot be ensured
Solution Approach 1:
The patent applies parameter changes by precisely controlling the refractive power of the third lens group within a specific range (−0.30 < f3/f < −0.05) and setting conditional expressions for focal length ratios (0.10 < f2/f1 < 0.40 and 0.50 < f3/f2 < 2.00). These parameter optimizations allow the negative third lens group to reduce overall length while maintaining sufficient back focus by balancing the diverging effect with the positive power of earlier lens groups.
Solution Approach 2:
The patent implements dynamics by allowing the first and second lens groups to move relative to each other during focusing operations. This dynamic adjustment enables the system to maintain proper image plane positioning across different focus distances while keeping the third lens group fixed, thereby preserving back focus requirements even with the compact negative power configuration.
2Device complexity
If the third lens group is formed as a fixed lens group to simplify the lens barrel mechanism, then the device complexity is reduced, but focusing requires shifting each lens group toward the object side increasing the moving amount
Solution Approach 1:
The patent applies segmentation by dividing the lens system into distinct functional groups: the first lens group (positive power) and second lens group (positive power) that move together for focusing, and the third lens group (negative power) that remains fixed. This segmentation simplifies the lens barrel mechanism by eliminating the need to move the third group while maintaining effective focusing capability through the coordinated movement of the first two groups.
3Object-affected harmful factors
If conventional antireflection coating techniques are used, then ghost images and flare are reduced, but the coating complexity increases with multiple layers requiring advanced growth techniques
Solution Approach 1:
The patent applies parameter changes by optimizing the refractive index and thickness parameters of the antireflection coating layers. By carefully selecting these parameters, the patent achieves effective reduction of ghost images and flare with a multi-layer coating structure, balancing performance improvement with manufacturing feasibility through established coating techniques.
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 effectively reduces the total lens length and moving amount, minimizes ghost images and flare, and maintains a sufficient back focus while ensuring an ample angle of view, thereby simplifying the lens barrel mechanism and enhancing optical performance.
Implementation Method 1
at least one optical surfaces of said first lens group is provided with an antireflection coating, and said antireflection coating includes at least, one layer formed by use of a wet process
Data Source
AI summary
An optical system includes, in order from an object side: a first lens group G1 having negative refractive power; and a second lens group G2 having positive refractive power; upon zooming from a wide-angle end state W to a telephoto end state T, a distance between the first lens group G1 and the second lens group G2 varying, and the second lens group G2 moving, and the second lens group G2 including a focusing lens group Gf that carries out focusing from an infinity object to a close object, and a decentering lens group Gs that is movable in a direction having a component perpendicular to an optical axis, thereby providing an optical system capable of establishing both of internal focusing and a decentering lens group with obtaining compactness and excellent optical performance, an optical apparatus equipped with the optical system, and a method for manufacturing the optical system.