Imaging Optical System Retro-Focus Lens Aberration Control
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Solution Overview
Problem
Imaging optical systems with large angles of view and high aperture ratios face challenges in achieving high-speed focusing and sufficient back focus while minimizing aberrations, particularly spherical and coma aberrations, which degrade image quality.
Innovation Solution
The imaging optical system includes a first lens unit with positive refractive power, a second lens unit with negative refractive power that moves during focusing, and a third lens unit with a retro-focus-type structure featuring concave surfaces and a positive lens, satisfying specific conditional expressions to control refractive powers and reduce aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the aperture ratio is increased to improve shutter speed and suppress camera shake, then the optical performance and low-light capability are improved, but the thickness of each lens is increased and the back focus is reduced
Solution Approach 1:
The imaging optical system is divided into multiple lens units (first lens unit with positive refractive power, second lens unit with negative refractive power, and third lens unit with positive refractive power). This segmentation allows each unit to be optimized independently, enabling the third lens unit to have a retro-focus structure that increases back focus while maintaining high aperture ratio and optical performance.
2Speed
If the inner focus system is used to perform focusing by moving the second lens unit, then the amount of movement is reduced and focusing speed is improved, but large variations in spherical aberration and coma aberration occur
Solution Approach 1:
The third lens unit is designed with specific local characteristics (retro-focus structure with concave surfaces facing each other with a largest air gap) to correct the aberrations that occur during focusing. This local optimization in the third lens unit compensates for the aberration variations caused by moving the second lens unit during inner focus operation.
Solution Approach 2:
The patent specifies particular parameter ranges for the lens units, including the conditional expression 0.70 < |f2/f| < 2.50 where f2 is the focal length of the second lens unit and f is the focal length of the entire system. These parameter constraints ensure that aberration variations remain within acceptable ranges during focusing while maintaining high focusing speed.
3Area of stationary object
If the imaging angle of view is increased to about 40° to 60° to achieve wide-angle imaging, then the field of view is expanded, but the back focus is reduced and aberration correction becomes more difficult
Solution Approach 1:
The third lens unit employs a retro-focus structure where the arrangement of lenses is inverted or reversed compared to a conventional telephoto structure. This inversion allows the back focus to be increased while maintaining a large angle of view, as the retro-focus configuration naturally provides a longer back focal length for wide-angle applications.
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 enables high-speed focusing, increased back focus, and reduced aberrations, thereby improving the optical performance and image quality of the imaging optical system with a large angle of view and high aperture ratio.
Implementation Method 1
an imaging optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, an aperture stop, and a third lens unit having a positive refractive power
Data Source
AI summary
An imaging optical system includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, an aperture stop, and a third lens unit having a positive refractive power. The second lens unit moves toward the image side during focusing from a far object to a near object. The third lens unit includes, in order from the object side to the image side, two lenses having concave surfaces that face each other with a largest air gap in the third lens unit provided therebetween, and a positive lens. A focal length of the entire imaging optical system and a focal length of the second lens unit are appropriately set.