Compact Imaging Lens with Inverted Retrofocus Group
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Solution Overview
Problem
Existing small-size imaging lenses for large-size imaging devices face challenges in reducing size while maintaining optical performance and portability, as they often require a long back focus and are costly due to complex lens structures.
Innovation Solution
The design incorporates a first lens group with a negative meniscus lens and a positive lens, followed by a second lens group with a positive and negative lens, optimizing curvature radii and refractive indices to achieve a compact, low-cost imaging lens with reduced back focus, using conditional formulas to ensure aberration correction and size reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a retrofocus-type arrangement with a negative lens closest to the object side is used, then a long back focus is secured, but the optical total length becomes long and the lens size increases
Solution Approach 1:
The patent inverts the conventional retrofocus arrangement by placing a positive lens closest to the object side instead of a negative lens. This reversal allows the lens to achieve a long back focus while maintaining a compact optical total length, resolving the contradiction between back focus length and overall lens size.
Solution Approach 2:
The patent employs specific conditional formulas that define parameter ranges for curvature radii and focal lengths. By optimizing these parameters within defined ranges, the lens achieves both a long back focus and compact size, transforming the trade-off into a balanced design through precise parameter control.
2Reliability
If a complex lens structure with multiple lens groups is used, then optical performance is improved, but manufacturing cost and device complexity increase
Solution Approach 1:
The patent divides the lens into two functional groups: a first lens group with positive refractive power closest to the object side, and a second lens group with negative refractive power. This segmentation allows each group to be optimized for its specific function while maintaining overall compactness and cost-effectiveness.
Solution Approach 2:
The patent designs the lens structure to serve multiple functions within a compact configuration. The first lens group handles both focusing and aberration correction, while the second lens group contributes to both image formation and compactness, reducing the need for additional specialized components.
3Length of moving object
If the lens size is reduced for portability, then the overall system size decreases, but maintaining optical performance and necessary back focus becomes difficult
Solution Approach 1:
By inverting the conventional lens arrangement and placing a positive lens closest to the object side, the patent achieves compact lens size while maintaining both necessary back focus and high optical performance, resolving the contradiction between size reduction and performance maintenance.
Solution Approach 2:
The patent uses conditional formulas to define optimal parameter ranges that enable compact lens dimensions while preserving optical performance. Through precise control of curvature radii and focal lengths within these ranges, the lens achieves small size without sacrificing image quality.
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 results in a thin, low-cost imaging lens that suppresses angle of incidence on the imaging device, achieves high optical performance, and reduces the overall size of the lens system while maintaining necessary back focus and correcting various aberrations effectively.
Implementation Method 1
The first lens group substantially consists of three or less lenses including a negative lens having a meniscus shape with its convex surface facing the object side and a positive lens cemented on the negative lens
Implementation Method 2
a positive lens cemented on the negative lens in this order from the object side
Data Source
AI summary
An imaging-lens substantially consists of a first-lens-group, a stop and a second-lens-group in this order from object-side. The first-lens-group substantially consists of three or less lenses including a negative-lens having meniscus-shape with convex-surface facing object-side and a positive-lens cemented on the negative-lens in this order from object-side. The second-lens-group substantially consists of a 21st-lens-group substantially consisting of a 21-1st-lens and a 21-2nd-lens and a 22nd-lens-group substantially consisting of a positive-lens. The 21-1st-lens is a positive-lens, an image-side-lens-surface of which has convex-shape facing image-side, and the absolute-value of a curvature-radius of the image-side-lens-surface of which is less than the absolute-value of a curvature-radius of an object-side-lens-surface thereof. The 21-2nd-lens is a negative-lens, an object-side-lens-surface of which has concave-shape facing object-side, and the absolute-value of a curvature-radius of the object-side-lens-surface of which is less than the absolute-value of a curvature-radius of an image-side-lens-surface thereof. A conditional-formula about optical-total-length and maximum-image-height is satisfied.