Imaging Lens Group Segmentation for Compact Back Focus
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Solution Overview
Problem
Conventional imaging optical systems with five lenses face challenges in reducing thickness and back focus, which hinders size reduction and optical performance in interchangeable lenses for single-lens reflex cameras.
Innovation Solution
An imaging optical system with an aperture stop, an object-side lens group of negative refracting power, and an image-side lens group of positive refracting power, comprising specific lens configurations and focal length ratios to achieve reduced thickness and maintained optical performance, including a cemented doublet for aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional five-lens imaging optical system is used, then optical performance can be improved, but the thickness becomes large relative to the back focus
Solution Approach 1:
The five-lens system is segmented into two functional groups: an object-side lens group with negative refracting power and an image-side lens group with positive refracting power. This segmentation allows independent optimization of each group's function, reducing overall thickness while maintaining optical performance through specialized aberration correction in each group.
Solution Approach 2:
The patent inverts the conventional lens arrangement by placing the aperture stop between the two lens groups, with the negative-power group on the object side and positive-power group on the image side. This inverted configuration achieves better thickness-to-back-focus ratios while correcting aberrations more effectively than conventional arrangements.
2Length of moving object
If the thickness is reduced, then the size of the imaging apparatus can be reduced, but it becomes difficult to ensure brightness and optical performance
Solution Approach 1:
Each lens group is designed with specific local optical properties: the object-side group uses negative refracting power with specific meniscus lens curvatures to control light angles, while the image-side group uses positive refracting power with a cemented doublet for chromatic aberration correction. This local optimization ensures high optical performance in a compact form.
Solution Approach 2:
The image-side lens group employs a cemented doublet combining lenses with different refractive indices and Abbe numbers (specifically satisfying 0.35 < v21/v22 < 0.80), creating a composite optical structure that corrects chromatic aberrations effectively while maintaining compact dimensions and high brightness.
3Reliability
If the aperture stop is positioned to correct distortion and Petzval sum, then spherical aberrations can be corrected, but the exit pupil cannot be spaced away from the image plane
Solution Approach 1:
The aperture stop serves as an intermediary element positioned between the two lens groups, mediating the optical paths to simultaneously correct distortion and Petzval sum while allowing the exit pupil to be properly spaced from the image plane. This intermediate positioning enables multiple aberration corrections without compromise.
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 ensures a compact design with improved optical performance, reduced thickness, and enhanced back focus, while maintaining image quality and correcting various aberrations, making it suitable for single-lens reflex cameras.
Implementation Method 1
an object-side positive meniscus lens convex on its object side and having positive refracting power and an object-side negative meniscus lens convex on its object side and having negative refracting power
Implementation Method 2
an image-side negative lens, an image-side first positive lens, and an image-side second positive lens, wherein the image-side negative lens and the image-side first positive lens form together a mutually cemented doublet
Implementation Method 3
The cemented doublet of the image-side negative lens L21 and the image-side first positive lens L22 is used for the image-side lens group so that correction of chromatic aberrations, etc. can be facilitated
Implementation Method 4
an aperture stop for limiting axial light beams
Implementation Method 5
the refracting powers of the lenses in the imaging optical system are symmetrically distributed, working for correction of distortion, Petzval s sum, spherical aberrations, etc.
Data Source
AI summary
An imaging optical system includes: an object-side lens group having, in order from its object side, an object-side positive meniscus lens that is convex on its object side and has positive refracting power, and an object side negative meniscus lens that is convex on its object side and has negative refracting power; and image-side lens group having, in order from its object side, an image-side negative lens, an image-side first positive lens and an image-side second positive lens. The image-side negative lens and the image-side first positive lens adjacent thereto form together a cemented doublet.