Internal Focus Lens Group Configuration for Compact Telephoto Design
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Solution Overview
Problem
Existing internal focus-type lenses face challenges in achieving compact size and superior optical performance due to insufficient size reduction and increased optical length, with prior art failing to effectively balance refractive power and lens movement during focusing.
Innovation Solution
The proposed imaging lens 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 second lens group moves along the optical axis to focus from infinity to a near point while the first and third lens groups are fixed, adhering to specific conditional expressions to achieve a compact and high-performance telephoto configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a telephoto configuration with a third lens group having negative refractive power is adopted, then the optical system size can be reduced, but the refractive power distribution and lens group spacing become complex making it difficult to achieve compact size
Solution Approach 1:
The patent applies parameter changes by precisely controlling the refractive power distribution among lens groups through specific conditional expressions. The third lens group's negative refractive power is optimized to satisfy -0.50 < f3/f1 < -0.10, and the lens group spacing is controlled by 0.30 < d1/f1 < 1.50, transforming a complex design problem into a manageable parameter optimization task that achieves compact size while maintaining optical performance
Solution Approach 2:
The patent applies local quality by assigning specific functional characteristics to different lens groups: the first lens group provides positive refractive power for overall convergence, the second lens group provides adjustable positive refractive power for focusing, and the third lens group provides negative refractive power for telephoto compression. Each lens group has optimized local optical properties that collectively achieve the compact telephoto configuration
2Reliability
If the first lens group length is increased to improve optical performance, then aberration correction is enhanced, but the total optical length increases reducing compactness
Solution Approach 1:
The patent applies segmentation by dividing the optical system into three functionally distinct lens groups with different refractive power characteristics. This segmentation allows each group to be optimized for its specific function: the first group for overall convergence, the second for focusing adjustment, and the third for telephoto compression. The segmentation enables compact total length while maintaining optical performance through distributed aberration correction across multiple groups
Solution Approach 2:
The patent applies the intermediary principle by using the second lens group as a mediator between the first and third lens groups. The second lens group's movable position and positive refractive power serve as an intermediate element that balances the optical paths, enabling the third lens group's negative power to effectively compress the overall optical length while the first lens group maintains proper convergence for high optical performance
3Adaptability or versatility
If the second lens group is made to move a large distance for focusing, then focusing range is improved, but the mechanical length and complexity of the lens barrel increase
Solution Approach 1:
The patent applies dynamics by making the second lens group movable along the optical axis while keeping the first and third lens groups fixed. This dynamic configuration allows the second lens group to adjust its position for focusing from infinity to close distances, providing versatile focusing range. The movable second group acts as the active element that adapts the optical system to different object distances without requiring the entire lens barrel to extend
4Length of stationary object
If the refractive power of the third lens group is increased to strengthen telephoto effect, then optical length is reduced, but aberration correction becomes difficult
Solution Approach 1:
The patent applies parameter changes by precisely controlling the third lens group's refractive power within the range -0.50 < f3/f1 < -0.10. This parameter optimization ensures the negative power is strong enough to achieve telephoto compression and reduce optical length, but not so strong as to create severe aberrations. The balanced parameter selection allows the third group to compress the optical path while the first and second groups compensate for aberrations through their positive refractive powers
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 enables a compact and lightweight internal focus-type lens with improved focusing speed and reduced size, maintaining high optical performance and preventing dust entry through airtight barrel structures without increasing the overall optical length.
Implementation Method 1
focusing from a point at infinity to an object at a near point is performed by moving the second lens group along the optical axis
Implementation Method 2
a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power
Data Source
AI summary
An imaging lens and an imaging device furnished with same, including a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, disposed in sequence from the object side, wherein zooming from a point at infinity to an object at the near point is performed by moving the second lens group along an optical axis toward the object side while affixing the first lens group and third lens group, and satisfying predetermined conditional expressions.