Endoscope Objective Optical System Compact Design
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Solution Overview
Problem
Conventional endoscope objective optical systems face challenges in achieving a compact size while maintaining image quality and preventing flare, particularly in ultrasmall-diameter endoscopes, due to difficulties in processing and assembling lenses with small diameters and complex frame structures.
Innovation Solution
The proposed endoscope objective optical system consists of an aperture stop, a front group with positive refractive power, and a rear group with positive refractive power, where the rear group is formed by joining a single lens with positive and negative refractive power and is joined to an imaging device, satisfying specific conditional expressions to reduce size and inhibit flare.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a retrofocus-type optical system with a concave lens is used to achieve a wider angle, then the angle of view is improved, but the lens thickness and outer diameter increase
Solution Approach 1:
The optical system is divided into multiple lens groups (first lens group with positive refractive power, second lens group with negative refractive power, third lens group with positive refractive power) instead of using a single concave lens. This segmentation allows achieving a wide angle of view while keeping individual lens elements smaller and thinner, resolving the contradiction between wide angle and compact size.
2Volume of moving object
If lens diameter is reduced to 1 mm or smaller for ultrasmall-diameter endoscopes, then the endoscope diameter is reduced, but lens processing becomes more difficult and requires higher precision
Solution Approach 1:
Instead of using a single small-diameter lens, the system uses multiple lens groups with different refractive powers. This allows distributing the optical function across several elements, making each individual lens easier to manufacture with standard precision while achieving the required small overall diameter through compact arrangement.
Solution Approach 2:
Each lens group is designed with specific refractive power characteristics (positive, negative, positive) to optimize local optical performance. This allows tailoring each lens element's properties to its specific function, making manufacturing more feasible while maintaining overall system performance in the ultrasmall diameter configuration.
3Length of stationary object
If lenses are disposed away from the imaging device to reduce air spaces, then the optical system length is reduced, but distortion effect decreases and wider angle becomes difficult to realize
Solution Approach 1:
The optical system is segmented into three lens groups with alternating refractive powers arranged in sequence between the object and imaging device. This segmentation allows the rear group (third lens group with positive refractive power) to be positioned close to the imaging device, maintaining short length while the front groups provide the necessary distortion control for wide angle capability.
4Length of stationary object
If the rear group with positive refractive power is disposed near the imaging device to achieve wide angle and compact size, then the optical system length and diameter are reduced, but processing ease and edge thickness may deteriorate
Solution Approach 1:
The rear positive lens group is segmented into three lens elements with alternating refractive powers. This segmentation allows the group to be positioned close to the imaging device for compactness while distributing the optical stress across multiple elements, maintaining adequate edge thickness and processing feasibility for each individual element.
Solution Approach 2:
Each lens element in the rear group is designed with specific refractive power and curvature characteristics optimized for its position and function. This local optimization allows the rear group to achieve wide angle correction near the imaging device while each element maintains manufacturable dimensions and edge thickness.
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 allows for a compact, wide-angle optical system with reduced flare by optimizing the refractive power distribution and lens configuration, ensuring ease of processing and assembly while maintaining image quality.
Implementation Method 1
an aperture stop; a front group having positive refractive power; and a rear group having positive refractive power
Implementation Method 2
a front group having positive refractive power; and a rear group having positive refractive power
Data Source
AI summary
Provided is an endoscope objective optical system including, in order from an object side, an aperture stop, a front group having positive refractive power, and a rear group having positive refractive power, in which the rear group is formed by joining a single lens having positive refractive power and a single lens having negative refractive power and is joined to an imaging device; a joining surface between the single lenses has positive refractive power; and the endoscope objective optical system satisfies following Conditional Expression (1):0.15<fF/fR<0.5, (1)where fF indicates a focal length of the front group, and fR indicates a focal length of the rear group.