Wide Angle Lens Back Focus Reduction via Asymmetric Cemented Groups
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Solution Overview
Problem
Conventional wide angle lenses for single-lens reflex cameras have a long back focus, leading to increased size and difficulty in correcting lateral chromatic aberration, while those for mirror-less cameras lack sufficient correction and require a small angle of incidence on the image plane, necessitating a reduction in overall lens system length and improved chromatic aberration correction.
Innovation Solution
A wide angle lens design comprising a first negative lens group, a second positive lens group with cemented lenses, and a third lens group with cemented lenses and aspherical surfaces, optimized to satisfy specific focal length and Abbe number conditions, allowing for reduced back focus and effective chromatic aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If retrofocus type lens system is used to secure sufficient back focus, then back focus is increased, but overall lens length is increased and lateral chromatic aberration correction becomes difficult
Solution Approach 1:
The lens system is divided into three distinct lens groups (first negative, second positive, third positive) with specific configurations. The first lens group includes a negative meniscus lens and other lenses, the second lens group includes cemented lenses, and the third lens group includes cemented lenses and aspherical surfaces. This segmentation allows each group to contribute differently to the overall optical performance, enabling sufficient back focus while controlling overall length.
Solution Approach 2:
The patent employs asymmetric lens configurations within each group. The first lens group has a negative meniscus lens with specific curvature relationships, the second and third groups have cemented lenses with asymmetric arrangements. This asymmetry allows optimization of light path control to achieve adequate back focus without proportionally increasing overall lens length.
2Reliability
If retrofocus type lens system is used, then back focus is secured, but lateral chromatic aberration correction becomes insufficient due to low symmetry with respect to the stop
Solution Approach 1:
The patent introduces asymmetric lens configurations within each group to improve symmetry with respect to the stop. The first lens group includes a negative meniscus lens with specific curvature relationships, the second and third groups have cemented lenses with asymmetric arrangements. This controlled asymmetry optimizes light path control to achieve adequate back focus while improving lateral chromatic aberration correction.
Solution Approach 2:
Different lens groups are assigned specific local qualities and functions. The first lens group focuses on negative refractive power with specific meniscus lens characteristics, the second lens group provides positive refractive power with cemented lenses, and the third lens group includes aspherical surfaces for aberration correction. This local optimization of each group's properties enables simultaneous achievement of back focus and chromatic aberration correction.
3Length of moving object
If negative-leading lens type is used for mirror-less cameras, then overall length is reduced, but lateral chromatic aberration correction remains insufficient
Solution Approach 1:
The patent employs composite lens structures with cemented lenses in the second and third lens groups. These cemented lenses combine different glass types with specific Abbe numbers to correct chromatic aberrations. The composite structure of multiple lens materials working together enables effective lateral chromatic aberration correction in a compact negative-leading lens configuration suitable for mirror-less cameras.
Solution Approach 2:
The patent incorporates aspherical surfaces in the third lens group to correct aberrations. The aspherical surfaces provide curved optical paths that spherical surfaces cannot achieve, enabling improved correction of lateral chromatic aberration while maintaining the compact negative-leading lens configuration required for mirror-less cameras.
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 design achieves a compact lens system with excellent optical performance, including well-corrected lateral chromatic aberration and reduced back focus, suitable for small imaging devices with a wide angle of view, such as mirror-less cameras.
Implementation Method 1
a third lens group having a positive refractive power, in order from the object side... the third lens group includes two pairs of cemented lenses and at least one aspherical surface
Implementation Method 2
the second lens group includes one pair of cemented lenses, and the third lens group includes two pairs of cemented lenses... favorable lateral chromatic aberration correction is required
Data Source
AI summary
A wide angle lens consists of a negative first lens group, a positive second lens group, a stop, and a positive third lens group in order from the object side. The first lens group includes two negative meniscus lenses, each with a convex surface on the object side. The second lens group includes one pair of cemented lenses. The third lens group includes two pairs of cemented lenses and at least one aspherical surface.