Wide-Angle Optical System Layout for Low-Shading Focusing
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Solution Overview
Problem
Existing wide angle lenses face challenges in achieving a small size, light weight, and high optical performance while minimizing aberrations and shading due to oblique incident light, particularly during focusing.
Innovation Solution
An optical system with a front lens unit having a positive refractive power and a rear lens unit with at least one positive lens, where the interval between these units changes during focusing, adhering to specific conditional expressions to optimize lens shapes and reduce aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a lens having a negative refractive power is arranged at the most image side to downsize the total lens length, then the total lens length is reduced, but the exit pupil becomes shorter and the incident angle of off-axial beam to the image pickup element becomes larger, causing shading and deterioration of optical performance
Solution Approach 1:
Instead of placing the negative refractive power lens at the image side (conventional approach), this patent inverts the arrangement by placing it at the object side. This inversion maintains the retrofocus wide angle structure while avoiding the exit pupil shortening problem that occurs when negative power lenses are positioned near the image plane, thereby preventing shading and optical performance deterioration.
Solution Approach 2:
The patent optimizes specific parameter ranges including the focal length ratio between front and rear lens units (0.3 < |f1/f2| < 1.0), the shape parameter of the image-side lens (0.1 < (G1R1+G1R2)/(G1R1-G1R2) < 0.5), and the interval changes during focusing. These parameter optimizations enable downsizing while maintaining adequate exit pupil length and controlling off-axial beam incident angles to prevent shading.
2Power
If the radius of curvature of the object side surface is smaller than that of the image side surface in the lens closest to the image side to achieve stronger positive refractive power, then the total lens system refractive power increases, but the curvature of field deteriorates mainly due to off-axial beam
Solution Approach 1:
The patent applies different shape characteristics to different lenses within the optical system. Specifically, the lens closest to the image side is designed with a controlled shape parameter (0.1 < (G1R1+G1R2)/(G1R1-G1R2) < 0.5) that balances refractive power with curvature of field correction, while other lenses have optimized shapes suited to their specific functions. This local optimization prevents the curvature of field deterioration that would result from uniformly applying strong positive power design.
Solution Approach 2:
The patent optimizes the shape parameter (G1R1+G1R2)/(G1R1-G1R2) of the image-side lens within a specific range (0.1 to 0.5) and controls the focal length ratio between lens units (0.3 < |f1/f2| < 1.0). These parameter optimizations enable the system to achieve sufficient refractive power while maintaining acceptable curvature of field, preventing deterioration caused by excessive off-axial beam convergence.
3Shape
If the height of off-axial beam becomes higher to achieve wide angle of view, then the wide angle performance is improved, but the deviations of curvature of field and distortion during focusing become larger
Solution Approach 1:
The patent divides the optical system into two functional segments: a front lens unit with negative refractive power handling off-axial beam convergence for wide angle performance, and a rear lens unit with positive refractive power maintaining image quality. This segmentation allows each unit to be optimized for its specific function, enabling wide angle of view while controlling curvature of field and distortion deviations during focusing.
Solution Approach 2:
The patent controls the interval LB between lens units during focusing within a specific range (0.05 < LB/LD < 0.30) and optimizes the focal length ratio (0.3 < |f1/f2| < 1.0). These parameter changes enable the system to maintain wide angle performance with adequate off-axial beam height while minimizing curvature of field and distortion deviations that would otherwise increase with higher off-axial beam paths.
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 wide angle lens with small size, light weight, and high optical performance by minimizing aberrations and shading, while allowing for effective focusing without increasing the total lens length.
Implementation Method 1
an optical system having a negative refractive power in the object side and an optical system having a positive refractive power in the image side
Data Source
AI summary
An optical system includes in order from an object side to an image side: a front lens unit having a positive refractive power; and a rear lens unit including a lens having a positive refractive power, in which the front lens unit includes a lens arranged closest to the object side has a negative refractive power, an interval between the front lens unit and the rear lens unit changes for focusing, a radius of curvature of an object-side surface of the lens having the positive refractive power arranged closest to the image side a radius of curvature on an object-side surface of the lens having the positive refractive power arranged closest to the image side are appropriately set.