Four-Lens Imaging System with Retrofocus Design for Wide Angle and Long Back Focus
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing imaging lenses face challenges in achieving a balance between compactness, wide angle of view, long back focus, and high optical performance, particularly in terms of brightness, distortion, and aberration correction, while maintaining telecentricity and appropriateness for downsizing.
Innovation Solution
A four-lens imaging lens system comprising a meniscus-shaped first lens with negative refractive power, a biconvex second lens with positive refractive power, a concave third lens with negative refractive power, and a convex fourth lens with positive power, arranged to satisfy specific conditional expressions for optimal performance, including the use of aspherical surfaces and resin materials for the third and fourth lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the focal length is shortened to broaden the angle of view, then the angle of view is broadened, but the back focus is reduced
Solution Approach 1:
The imaging lens is divided into four distinct lens groups (first lens with negative power, second lens with positive power, third lens with negative power, fourth lens with positive power). This segmentation allows each group to contribute differently to the overall optical performance, enabling the system to achieve both a broad angle of view and sufficient back focus by distributing the optical functions across multiple elements rather than relying on a single focal length adjustment.
Solution Approach 2:
The patent employs a retrofocus type lens system that inverts the conventional arrangement by placing a negative power lens group at the object side followed by positive power lens groups. This inverted configuration (negative-positive-positive power sequence) is characteristic of retrofocus designs, which specifically address the contradiction by expanding the angle of view while maintaining an extended back focus distance, opposite to the typical behavior of simple focal length reduction.
2Volume of moving object
If the distance from the exit pupil to the image plane is reduced to downsize the device, then the device size is reduced, but telecentricity is compromised and uneven illuminance increases
Solution Approach 1:
The patent carefully controls and optimizes specific optical parameters including the distance L12 between the first and second lenses, the focal lengths and refractive powers of each lens group, and the positions of the exit pupil and image plane. By adjusting these parameters within specific ranges and satisfying conditional expressions, the design achieves telecentricity (where the exit pupil is at infinity) while maintaining a compact overall size, thus resolving the contradiction between downsizing and maintaining telecentric properties.
3Device complexity
If a simple lens structure is used to reduce complexity, then the structure is simplified, but aberration correction and optical performance are degraded
Solution Approach 1:
The patent incorporates aspherical surfaces on one or both surfaces of at least one lens element. These asymmetrical surfaces deviate from traditional spherical geometry, allowing for superior correction of spherical aberration and other optical imperfections. The aspherical design enables the lens system to achieve high optical performance with only four lens elements, maintaining relative structural simplicity while dramatically improving aberration correction compared to conventional spherical lens designs.
Solution Approach 2:
The patent specifies different refractive indices and Abbe numbers for each lens element (first lens: nd=1.589, νd=36.1; second lens: nd=1.755, νd=50.5; third lens: nd=1.634, νd=23.6; fourth lens: nd=1.534, νd=56.0). This composite approach using materials with varying optical properties allows for effective chromatic aberration correction and optimized overall performance. By combining materials with different dispersion characteristics, the system achieves superior color correction and image quality without requiring a more complex multi-element design.
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 enables a compact, bright imaging lens with a wide angle of view and long back focus, achieving improved optical performance by effectively correcting various aberrations and maintaining telecentricity, thus addressing the limitations of existing lenses.
Implementation Method 1
a first lens having a meniscus shape with a convex surface on the object side and a negative refractive power
Implementation Method 2
a second lens having a biconvex shape and a positive refractive power
Implementation Method 3
a third lens having a concave surface on the image side and a negative refractive power
Implementation Method 4
a fourth lens having a convex surface on the object side and a positive power
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
[Problems to be Solved] In imaging lenses, to realize a compact and bright lens system having a wide angle of view and a long back focus. [Means for Solving the Problems] An imaging lens which includes a first lens (L1) having a meniscus shape with a convex surface of the object side and a negative refractive power, a second lens (L2) having a biconvex shape and a positive refractive power, a third lens (L3) having a concave surface on the image side and a negative refractive power, and a fourth lens (L4) having a convex surface on the object side and a positive refractive power arranged in order from the object side, and being configured to satisfy a conditional expressions (1) L12/f<0.82 and (2) :2.3<L12×R2F2/f2 <10.0 simultaneously, where L12: is the distance between the first lens (L1) and the second lens (L2) on the optical axis, f is the focal length of the entire lens system, and R2F is the radius of curvature of the object side lens surface of the second lens (L2).