Objective Optical System with Moving Lens Group for Endoscope Focusing
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Solution Overview
Problem
Existing endoscope objective lenses lack sufficient water resistance, are prone to scratches, and experience significant image plane fluctuations and angle of view changes during focusing, especially when using high-pixel-count CCDs, which degrades image quality and observation depth.
Innovation Solution
An objective optical system comprising a first group with a plano-concave lens and a meniscus lens, a second group with a positive meniscus lens that moves for focusing, and a third group with a positive lens and a joined positive and negative lens, optimized to maintain a constant angle of view and correct distortion, satisfying specific conditional expressions to enhance depth and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel count of CCD is increased to improve diagnostic accuracy, then image quality is improved, but observation depth is decreased due to the need to decrease Fno and increase focal length
Solution Approach 1:
The objective lens is divided into three distinct groups (first group with negative power, second group with positive power, third group with positive power) that can move independently. This segmentation allows the second group to be moved for focusing while maintaining the overall optical parameters needed for both high image quality and sufficient observation depth.
Solution Approach 2:
The second group of the objective lens is designed to move along the optical axis for focusing, transforming a static optical system into a dynamic one. This dynamic adjustment enables the system to maintain optimal performance across different object distances while preserving both image quality and observation depth.
2Length of stationary object
If a meniscus lens is used to increase observation depth, then observation depth is improved, but the lens protrudes at the distal end causing insufficient water break and frequent scratches
Solution Approach 1:
Instead of using a conventional meniscus lens shape that protrudes outward, the first group employs a plano-concave lens with a flat outer surface. This inverted approach achieves the desired optical effect of increased observation depth while eliminating the protrusion that causes water break issues and scratches.
Solution Approach 2:
The optical system uses different lens shapes in different groups: the first group uses a plano-concave lens with a flat surface for water resistance, while the second and third groups use meniscus lenses to provide the necessary optical power and depth. This local differentiation allows each lens to optimize for its specific function.
3Length of stationary object
If existing objective lenses are used to maintain wide observation depth, then observation depth is preserved, but significant image plane fluctuations occur during focusing
Solution Approach 1:
The system carefully controls the power ratio between the first and second groups within a specific range (0.3 < |f1/f2| < 1.5) and sets the focal length ratio of the meniscus lens to satisfy conditional expressions. These parameter optimizations ensure that when the second group moves for focusing, the image plane remains stable with minimal fluctuation.
Solution Approach 2:
Instead of using complex mechanical focusing mechanisms that cause large image plane shifts, the patent employs an optical design where the movement of the second group is precisely controlled within specific distance ranges, substituting mechanical precision with optical parameter optimization.
4Ease of operation
If existing objective lenses are used for near observation, then near focusing is achieved, but the angle of view changes significantly from wide to extremely narrow
Solution Approach 1:
The dynamic movement of the second group is designed to move within a controlled range that maintains angle of view consistency. The power ratio between groups and the focal length parameters are optimized to ensure that focusing from far to near objects does not cause extreme changes in the angle of view.
Solution Approach 2:
The optical parameters are carefully selected to satisfy conditional expressions that limit the change in angle of view during focusing. The power ratio and focal length relationships are optimized to maintain adaptability across different observation distances.
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 system achieves a high-performance objective optical system with reduced distortion and image plane fluctuations, enabling effective focusing from far to near object points while maintaining image quality and depth, compatible with high-pixel-count image acquisition devices.
Implementation Method 1
the second group includes a positive meniscus lens whose convex surface is towards the object side and moves in a direction of an optical axis to perform focusing
Data Source
AI summary
Provided is a high-performance objective optical system which is compatible with a high-pixel-count image acquisition device, in which focusing can be achieved according to a change in object point distance and which has sufficient depth of field at the individual object point distances. Provided is an objective optical system (1) including, in order from an object side, a first group (G1), a second group (G2), and a third group (G3), in which the first group (G1) includes, in order from the object side, a plano-concave lens (L1) and a meniscus lens (L2) whose convex surface is towards an image side and in which the second group (G2) includes a positive meniscus lens whose convex surface is towards the object side and moves in the direction of an optical axis to perform focusing.