Imaging Lens Inner Focus Aberration Control
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Solution Overview
Problem
Conventional telephoto-type imaging lenses with an inner focus system and small F-number face challenges in maintaining good optical performance across a wide range of object distances due to significant aberration fluctuations, and increasing the number of lenses leads to size increases, which is undesirable.
Innovation Solution
The imaging lens configuration includes a first lens group with at least three positive and two negative lenses, a second lens group with a negative lens, and a third lens group with at least three positive and two negative lenses, where only the second lens group moves during focusing, satisfying specific condition expressions to correct aberrations while minimizing size increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of lenses is increased to maintain good optical performance for a wide range of object distance, then optical performance is improved, but the size of the lens system increases
Solution Approach 1:
The lens system is divided into three lens groups (first lens group with positive refractive power, second lens group with negative refractive power, and third lens group with positive refractive power) with specific lens configurations. The first and third lens groups each contain at least three positive lenses and at least two negative lenses, while the second lens group contains a negative lens. This segmentation allows for effective aberration correction without requiring an excessive total number of lenses, thus maintaining optical performance while controlling system size.
Solution Approach 2:
Different lens groups are assigned specific functions and configurations to correct different types of aberrations at different locations in the optical path. The first lens group corrects aberrations for distant objects, the second lens group (which moves during focusing) corrects aberrations for close-up objects, and the third lens group refines the overall image quality. This local optimization allows each lens group to be designed with minimal lenses for its specific purpose, reducing the total system size.
2Speed
If a telephoto-type imaging lens with small F-number and inner focus system is designed, then focusing speed is improved, but aberration fluctuation increases making it difficult to maintain good optical performance
Solution Approach 1:
The second lens group, which has a negative refractive power and contains a negative lens, is designed to move along the optical axis during focusing operations. This dynamic configuration allows the lens system to quickly adjust focus from infinity to close-up distances without moving the entire lens assembly, maintaining fast focusing speed. The specific configuration of this movable group ensures that aberrations remain well-corrected throughout the focusing range.
Solution Approach 2:
The patent specifies precise parameter ranges for the lens configuration, including the condition that the first lens group comprises at least three positive lenses and at least two negative lenses, the second lens group comprises a negative lens, and the third lens group comprises at least three positive lenses and at least two negative lenses. These parameter specifications ensure that the lens system maintains optimal optical performance across the entire focusing range while enabling fast inner focus operation.
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 maintains high optical performance with reduced aberration fluctuations and size increase, achieving a small F-number and effective correction of spherical and chromatic aberrations across a wide range of object distances.
Implementation Method 1
an imaging lens consists of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a stop, and a third lens group having a positive refractive power
Data Source
AI summary
An imaging lens consists essentially of, in order from the object side, a positive first lens group, a negative second lens group, a stop, and a positive third lens group. Focusing is effected by moving only the second lens group along the optical axis direction. Each of the first lens group and the third lens group includes at least three positive lenses and at least two negative lenses. The imaging lens satisfies the condition expression (1) below:0.53<−f2/f<0.9 (1),where f2 is a focal length of the second lens group, and f is a focal length of the entire system when the imaging lens is focused on an object at infinity.