Objective Optical System with Movable Lens Group for Endoscope
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Solution Overview
Problem
The existing objective optical systems for endoscopes with high-pixel image sensors face challenges in maintaining a suitable depth of field and image quality due to the narrow depth of field caused by increased pixel density, requiring a focusing function that is not adequately addressed by conventional designs.
Innovation Solution
An objective optical system comprising three lens groups with specific refractive powers, where focusing is achieved by moving the second group, and a planoconvex positive lens nearest to the image is affixed directly to the image pickup surface or a cover glass, satisfying conditional expressions to optimize image plane positioning and reduce manufacturing-error sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels of the image sensor is increased to improve image quality, then the image quality is improved, but the depth of field becomes narrow
Solution Approach 1:
The patent implements a focusing mechanism that moves the second lens group (negative refractive power) along the optical axis to dynamically adjust the depth of field. This allows the system to adapt between capturing close-up images and distant images, resolving the contradiction between high pixel density requiring small F-number and the need for adequate depth of field coverage
2Measurement precision
If the F-number is made small to avoid diffraction degradation, then the image quality is improved, but the depth of field becomes narrow
Solution Approach 1:
By making the second lens group movable along the optical axis, the system can dynamically adjust focusing while maintaining a small F-number for high image quality. The movement range of the second lens group compensates for the narrow depth of field inherent in small F-number systems, allowing both high image quality and adequate depth of field to be achieved
3Measurement precision
If the focal length is made large to accommodate large image sensor, then the image quality is improved, but the device size becomes large
Solution Approach 1:
The patent divides the optical system into three distinct lens groups with different refractive powers (positive, negative, positive). This segmentation allows the use of a large image sensor for high image quality while keeping the overall focal length and device size manageable through the coordinated design of multiple lens groups with opposing refractive powers
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 enhances the optical system's performance for high-definition small-size image sensors by maintaining image quality and reducing error sensitivity, allowing for effective focusing and improved image capture with a small-size camera.
Implementation Method 1
a lens nearest to image is a planoconvex positive lens having a convex surface directed toward the object side
Implementation Method 2
focusing is carried out by moving the second group
Data Source
AI summary
The objective optical system consists of order from an object side, a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power, wherein focusing is carried out by moving the second group, and a lens nearest to image is a planoconvex positive lens having a convex surface directed toward the object side, and a flat surface of the planoconvex positive lens is either affixed directly to an image pickup surface or cemented to a cover glass formed on the image pickup surface, and the objective optical system satisfies the following conditional expression (1).5<ff/f<8 (1)where,ff denotes a focal length of the planoconvex positive lens disposed nearest to image, andf denotes a focal length of the overall objective optical system at the time of normal observation.