Variable Magnification Optical System Compact Barrel Autofocus
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Solution Overview
Problem
Conventional variable magnification optical systems face challenges in achieving high-speed auto focusing and quiet operation while maintaining a compact barrel size, due to a focusing lens group that is insufficiently lightweight, leading to increased motor or actuator size and aberration variations during zooming and focusing.
Innovation Solution
A variable magnification optical system comprising specific lens groups with varying distances and refractive powers, where the third lens group moves along the optical axis, and conditional expressions are satisfied to optimize focal lengths and aberration correction, allowing for a downsized and lighter focusing lens group.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the focusing lens group is made lighter to achieve high-speed auto focusing, then the auto focusing speed is improved, but the barrel size increases due to larger motor or actuator requirements
Solution Approach 1:
The optical system is divided into multiple lens groups (first through fifth lens groups) with different functions. The third lens group is specifically designated as the focusing lens group and is separated from other lens groups, allowing independent optimization of its weight and focusing mechanism without affecting the entire optical system structure.
Solution Approach 2:
The patent applies specific conditional expressions (0.30 < f3/fw < 0.50 and 0.60 < f4/fw < 0.90) to control the focal length ratios of the lens groups. By optimizing these optical parameters, the focusing lens group weight is reduced to enable high-speed autofocus while maintaining compact barrel dimensions through proper optical design.
2Object-affected harmful factors
If the focusing lens group weight is reduced to improve quietness during auto focusing, then the noise level is decreased, but the aberration correction becomes more difficult
Solution Approach 1:
Different lens groups are assigned different refractive powers and optical characteristics. The third lens group (focusing group) has positive refractive power with specific focal length ratio, while the fourth lens group has negative refractive power. This local optimization of optical properties allows the lightweight focusing group to maintain good aberration correction capability.
Solution Approach 2:
The patent optimizes the refractive power distribution across lens groups by controlling the focal length ratios (f3/fw and f4/fw). This parameter optimization ensures that even with a reduced-weight focusing lens group, the overall aberration correction remains effective through proper optical design.
3Length of stationary object
If the barrel size is reduced to make the system more compact, then the portability is improved, but the focusing lens group cannot be sufficiently lightweighted
Solution Approach 1:
By segmenting the optical system into five distinct lens groups with specific functional assignments, the patent isolates the focusing function to the third lens group. This segmentation allows the focusing group to be optimized for minimal weight independently of the overall barrel size constraints.
Solution Approach 2:
The patent uses conditional expressions to control the focal length ratios of the lens groups relative to the overall system focal length (fw). By optimizing these parameters, the design achieves a balance where the focusing lens group is sufficiently lightweight for high-speed autofocus while the entire system maintains a compact barrel configuration.
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
Enables high-speed auto focusing with good quietness and suppresses aberration variations during zooming and focusing without increasing the barrel size, while maintaining effective aberration correction across different focal lengths.
Implementation Method 1
a third lens group having positive refractive power... upon focusing from an infinite distance object to a close distance object, the third lens group being moved along an optical axis
Implementation Method 2
a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; a fourth lens group... the following conditional expression being satisfied: 0.60 < f3/f4
Data Source
AI summary
A variable magnification optical system is provided which includes, in order from an object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4, and a subsequent lens group GR. Upon zooming, each of distances between the first lens group G1 and the second lens group G2, between the second lens group G2 and the third lens group G3, between the third lens group G3 and the fourth lens group G4, between the fourth lens group G4 and the subsequent lens group GR is varied, and upon focusing, the third lens group G3 is moved along an optical axis. A predetermined condition is satisfied. Consequently, the optical system enables a focusing lens group to be downsized and made light and also enables high speed auto focusing and quietness upon auto focusing to be realized without increasing the size of a barrel. Variation in aberration upon zooming from a wide-angle end state to a telephoto end state and variation in aberration upon focusing from an infinite distance object to a close distance object are well suppressed. Also, an optical apparatus and a method for manufacturing the variable magnification optical system are provided.