Zoom Lens Rear Group Segmentation for Fast Autofocus
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Solution Overview
Problem
Existing zoom lens systems face challenges in achieving fast autofocus speeds due to the weight and moving amount of the focusing lens group, which is exacerbated by the need to move multiple lenses for focusing, leading to inefficiencies in focusing speed and accuracy.
Innovation Solution
A zoom lens system comprising a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, where the first lens group is divided into a front and rear lens group, and focusing is achieved by moving only the rear lens group, optimizing the refractive power and moving amounts to reduce weight and increase focusing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple lenses are moved for focusing, then focusing coverage is improved, but focusing speed deteriorates due to increased weight
Solution Approach 1:
The first lens group is divided into a front lens group (G1a) and a rear lens group (G1b), where only the rear lens group is moved for focusing. This segmentation allows the system to maintain effective focusing coverage while reducing the weight and moving amount of the focusing lens group, thereby improving focusing speed.
2Speed
If the rear lens group is made lighter, then focusing speed is improved, but focusing precision may deteriorate
Solution Approach 1:
The patent optimizes specific parameters of the rear lens group including its focal length (f1b), refractive index (n1b), and Abbe number (ν1b) to maintain focusing precision while reducing weight. The conditional expressions ensure that the rear lens group has sufficient optical power and appropriate dispersion characteristics to achieve accurate focusing despite its reduced mass.
3Speed
If the moving amount of the rear lens group is reduced, then focusing speed is improved, but focusing range may deteriorate
Solution Approach 1:
The patent assigns specific optical properties to the rear lens group, including its focal length ratio (0.35≤f1b/f1<0.65) and refractive characteristics, to maximize focusing efficiency within a limited moving range. The local optimization of the rear lens group's optical quality enables it to achieve adequate focusing range despite minimal displacement.
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 results in a lighter focusing lens system that enables faster autofocus speeds by minimizing the moving amount of the rear lens group, improving focusing accuracy, and maintaining effective aberration correction across various focal lengths.
Implementation Method 1
a rear lens group having positive refractive power... Focusing from infinity to a close object is carried out by moving only the rear lens group to the object
Implementation Method 2
a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power
Implementation Method 3
When a state of lens group positions varies from a wide-angle end state to a telephoto end state
Data Source
AI summary
Providing a zoom lens system that satisfies making the focusing lens light and reducing a moving amount for focusing, simultaneously. The zoom lens system includes a first lens group having positive power, a second lens group having negative power and a third lens group having positive power. When zooming from a wide-angle end state to a telephoto end state, at least the first and third lens groups are moved such that a distance between the first and second lens groups increases, and a distance between the second and third lens groups decreases. The first lens group is composed of a front lens group with positive power having at least one negative lens and at least one positive lens, and a rear lens group with positive power having one positive lens. Focusing from infinity to a close object is carried out by moving only the rear lens group to the object.