Compact Imaging Lens with Aspherical Second Group
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Solution Overview
Problem
Existing imaging lenses with retrofocus power arrangements face challenges in achieving both long back focus and high optical performance, which can lead to increased optical length, making them unsuitable for downsizing, especially in compact and portable imaging devices with large image sensors.
Innovation Solution
A compact imaging lens configuration comprising a first lens group with positive refractive power, an aperture stop, a second lens group with negative refractive power, and a third lens group with positive refractive power, where the second lens group includes at least one aspherical surface, allowing for focus adjustment by moving the first and second lens groups, and satisfying specific conditional expressions for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a retrofocus power arrangement is used to achieve long back focus, then the back focus length is improved, but the optical length is extended and the lens becomes larger
Solution Approach 1:
The patent makes the first and second lens groups movable to enable focus adjustment. By moving these lens groups, the system dynamically adjusts focus while maintaining a compact overall structure, resolving the contradiction between achieving adequate back focus and keeping the optical length short.
Solution Approach 2:
The patent introduces aspherical surfaces in the second lens group and specifies particular focal length ratios (f/f2 between -0.51 and -0.09) to optimize the optical parameters. This allows the system to achieve long back focus with reduced optical length by changing the geometric parameters of the lens surfaces.
2Length of moving object
If the optical length is extended to ensure long back focus, then the back focus requirement is met, but the imaging device cannot be downsized
Solution Approach 1:
By making lens groups movable, the system achieves focus adjustment without requiring a long fixed optical path. This dynamic approach allows compact device volume while maintaining adequate back focus through active focus control.
Solution Approach 2:
The aspherical surfaces in the second lens group enable more efficient light path control, allowing the system to achieve the required back focus length with a shorter overall optical path, thus reducing device volume.
3Length of stationary object
If a compact lens configuration is used to reduce optical length, then the device size is reduced, but achieving high optical performance becomes difficult
Solution Approach 1:
The aspherical surfaces in the second lens group correct spherical aberration and other optical distortions that typically arise in compact lens designs. This maintains high optical performance despite the reduced optical length.
Solution Approach 2:
By optimizing the focal length ratio (f/f2) and other parameters, the patent achieves high optical performance in a compact configuration. The specific parameter ranges specified ensure aberration control while maintaining short optical length.
4Reliability
If more lenses are added to improve optical performance, then the optical performance is improved, but the optical length and device complexity increase
Solution Approach 1:
The aspherical surfaces provide superior aberration correction compared to multiple spherical lenses, achieving high optical performance with fewer lens elements and shorter optical length.
Solution Approach 2:
The combination of spherical and aspherical lens surfaces creates a composite optical system that achieves high performance with optimized lens count, avoiding the need for additional lenses that would increase optical length.
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 configuration results in a compact imaging lens that maintains satisfactory optical performance compatible with large image sensors, effectively correcting various aberrations while reducing the overall optical length, making it suitable for use in portable devices.
Implementation Method 1
the second lens group is composed of three lenses or less, includes one negative lens and one positive lens, and has at least one aspherical surface
Data Source
AI summary
An imaging lens composed of a positive first lens group, an aperture stop, a negative second lens group, and a positive third lens group disposed in order from the object side. The first lens group includes one negative lens and one positive lens disposed in order from the object side. The second lens group includes one negative lens and one positive lens, has at least one aspherical surface, and is composed of three lenses or less, in which the most object side surface and the most image side surface of the second lens group are concave and convex surfaces respectively. The third lens group is composed of a negative lens with a concave surface on the object side and one or more positive lenses disposed in order from the object side.