Reduction Optical System Back Focus Optimization
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Solution Overview
Problem
Existing reduction optical systems for image pickup apparatuses face challenges in achieving a small size, sufficient back focus, and high optical performance, with prior systems either having insufficient back focus or large lens diameters due to the placement and refractive power of negative lenses.
Innovation Solution
A reduction optical system is designed with a positive lens element closest to the object side and another positive lens element closest to the image side, accompanied by a negative lens in between, which satisfies specific conditional expressions for refractive power ratios and indices to optimize size and optical performance, including the placement of the rear principal point for sufficient back focus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a negative lens with the strongest refractive power is disposed closest to the image side, then the reduction optical system can achieve high optical performance, but the back focus length becomes insufficient
Solution Approach 1:
The patent inverts the conventional arrangement by placing the negative lens closest to the object side instead of the image side. This inversion allows the rear principal point to be positioned on the image side, thereby achieving sufficient back focus length while maintaining high optical performance through proper refractive power distribution.
Solution Approach 2:
The patent changes the refractive power parameters by specifying that the negative lens closest to the object side has a refractive power satisfying specific conditional expressions. This parameter optimization enables the system to achieve both compact size and sufficient back focus by carefully controlling the strength and position of each lens element.
2Volume of moving object
If a negative lens is placed on the object side, then the system can achieve a compact design, but the diameter of lenses on the image side becomes large
Solution Approach 1:
The patent applies local quality by giving different refractive power characteristics to different lens elements. The negative lens on the object side has specifically controlled refractive power to manage beam expansion, while positive lenses on the image side have optimized powers to control beam convergence, thereby reducing lens diameters locally where needed.
Solution Approach 2:
The patent changes the refractive power parameters of individual lens elements to optimize the beam path. By controlling the refractive power of the negative lens and the subsequent positive lenses, the system achieves compact overall size while keeping individual lens diameters small through proper parameter selection.
3Volume of moving object
If the reduction optical system is designed for small size, then mobility is improved, but achieving sufficient back focus and high optical performance becomes difficult
Solution Approach 1:
The patent segments the reduction optical system into distinct functional groups: a negative lens on the object side for beam divergence control, and positive lenses on the image side for beam convergence and focus. This segmentation allows each element to be optimized for its specific function, achieving compact size while maintaining high optical performance through coordinated design of the segmented components.
Solution Approach 2:
The patent inverts the conventional lens arrangement to place the negative lens on the object side, which enables the rear principal point to fall on the image side. This inversion is key to achieving sufficient back focus in a compact system, as it allows the optical design to meet both the small size requirement and the back focus requirement simultaneously.
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 reduction optical system that achieves a balance of small size, sufficient back focus, and high optical performance by controlling refractive power and curvature, reducing aberrations such as chromatic and spherical aberrations, while ensuring the rear principal point is positioned correctly on the image side.
Implementation Method 1
a reduction optical system including a first lens element (single lens or cemented lens) disposed closest to an object side and having positive refractive power, a second lens element (single lens or cemented lens) disposed closest to an image side and having positive refractive power, a positive lens... and a negative lens... between the first lens element and the second lens element
Data Source
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AI summary
A reduction optical system disposed on an image side of a main optical system, a composite focal length of the main optical system and the reduction optical system being shorter than a focal length of the main optical system, includes a first lens element disposed closest to an object side and having a positive refractive power, a second lens element disposed closest to an image side and having a positive refractive power, and a positive lens and a negative lens disposed between the first lens element and the second lens element.