Endoscope Objective Optical System with Movable Lens Group
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Solution Overview
Problem
Endoscope objective optical systems face challenges in maintaining image quality due to increased pixel density, requiring a smaller F-number which narrows the depth of field, and achieving a long back focus while minimizing aberrations.
Innovation Solution
The objective optical system is designed with a configuration of a first group having negative refractive power, a second group with positive refractive power that moves along the optical axis, and a third group with positive refractive power, including a positive cemented lens and a positive lens, to satisfy specific conditional expressions that balance back focus and focal length, allowing for a long back focus and reduced aberration fluctuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels of the image pickup element is increased, then the image resolution is improved, but the F-number must be made smaller which narrows the depth of field
Solution Approach 1:
The patent applies the dynamics principle by making the second lens group movable along the optical axis to provide a focusing function. This dynamic adjustment allows the system to maintain sharp focus across varying object distances, effectively addressing the depth of field limitation caused by the small F-number required for high-resolution imaging with increased pixel density.
2Length of stationary object
If a long back focus is required to accommodate optical members such as prisms, then the optical path length is increased, but the overall system length becomes longer
Solution Approach 1:
The patent applies parameter changes by carefully designing the focal lengths and refractive powers of the lens groups to satisfy specific conditional expressions. The system achieves a back focus of FB/f = 4-7 by optimizing the optical parameters of each lens group, allowing adequate space for optical members while controlling the overall system length through precise parameter selection.
3Reliability
If the F-number is made small to prevent image quality degradation, then the aperture is enlarged, but the depth of field becomes narrow
Solution Approach 1:
The movable second lens group provides dynamic focusing capability that compensates for the narrow depth of field inherent in small F-number systems. By adjusting the position of the second lens group, the system can maintain acceptable focus across a range of object distances, effectively extending the usable depth of field while preserving the benefits of the small F-number for image quality.
4Adaptability or versatility
If a focusing function is added to the optical system to secure depth of field, then the observation range is extended, but the aberration fluctuation increases
Solution Approach 1:
The patent applies parameter changes by designing the lens groups with specific refractive powers and focal lengths that satisfy conditional expressions. The first lens group has negative refractive power, the second has positive refractive power, and the third has positive refractive power. This careful parameter selection ensures that aberration fluctuation during focusing remains within acceptable limits while maintaining the extended depth of field provided by the focusing function.
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-quality endoscopic images with a long back focus and minimal aberration fluctuation, maintaining image quality across varying observation states with a lesser number of lenses.
Implementation Method 1
a positive cemented lens and a positive lens, and observation from a normal observation state up to a close observation state is possible by moving the second group along an optical axis, and the first group includes a cemented lens
Implementation Method 2
the cemented lens is a negative cemented lens
Data Source
AI summary
There is provided an objective optical system for endoscope with a lesser number of lenses and high-performance optical characteristics, equipped with a long back focus and a focusing function, and in which the aberration fluctuation accompanied by focusing is small.The objective optical system for endoscope includes in order from an object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power, wherein the third group includes in order from the object side, a positive cemented lens and a positive lens, and observation from a normal observation state up to a close observation state is possible by moving the second group along an optical axis and the first group includes a cemented lens, and the first group includes in order from the object side, a negative lens having a concave surface directed toward an image side, and the cemented lens, and the cemented lens is a negative cemented lens, and the second group includes a positive meniscus lens having a convex surface directed toward the object side, and the objective optical system for endoscope satisfies the following conditional expression (1).4≦FB/f≦7 (1)where,FB denotes a hack focus of the objective optical system for endoscope, andf denotes a focal length of the overall objective optical system for endoscope in the normal observation state.