Objective Optical System for Endoscope Focusing
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Solution Overview
Problem
Endoscope objective lenses with a large number of pixels face a narrow depth of field due to the need for smaller F-number and longer focal length, requiring a focusing function that maintains the angle of view without significant fluctuations.
Innovation Solution
An objective optical system comprising a first unit with positive refractive power, a second unit with negative refractive power, and a third unit with positive refractive power, where focusing is achieved by moving the second unit, with specific conditional expressions ensuring optimal focal lengths and lens movements to maintain image quality and depth of field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels of CCD is increased to improve image quality, then image quality is improved, but the depth of field becomes narrow
Solution Approach 1:
The patent implements a focusing mechanism that moves specific lens units (the second lens unit with negative refractive power, and optionally the third lens unit with positive refractive power) to dynamically adjust the focal position. This dynamic adjustment allows the system to maintain adequate depth of field while supporting high-pixel CCD sensors by compensating for the naturally narrower depth of field through active focusing capability.
2Length of moving object
If a focusing function is added to maintain depth of field, then depth of field is maintained, but the angle of view changes during focusing
Solution Approach 1:
The patent assigns different functional characteristics to different lens units. The second lens unit (negative refractive power) and third lens unit (positive refractive power) are designed with specific focal length relationships (|f2| < 0.5×|f1| and f3 < 2.0×f1) that allow them to contribute to focusing while minimizing angle of view change. This localized optimization of lens unit properties enables selective adjustment during focusing.
Solution Approach 2:
The patent employs specific conditional expressions that constrain the focal lengths of individual lens units relative to each other (|f2| < 0.5×|f1| and f3 < 2.0×f1). These parameter relationships ensure that when lens units are moved for focusing, the overall angle of view remains substantially constant. The parameter constraints guide the design of lens unit powers and movements.
3Measurement precision
If the F-number is made small to avoid diffraction degradation, then image quality is maintained, but the depth of field becomes narrow
Solution Approach 1:
The focusing mechanism compensates for the narrow depth of field inherent in small F-number systems. By moving the second and third lens units during focusing operations, the system maintains adequate depth of field coverage while preserving the benefits of small F-number operation for reducing diffraction effects and maintaining image quality.
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 solution provides an objective optical system with a small change in angle of view during focusing, maintaining adequate depth of field at various object distances and supporting high-pixel image pickup elements with superior performance.
Implementation Method 1
An objective optical system includes in order from an object side, a first unit having a positive refractive power, a second unit having a negative refractive power, and a third unit having a positive refractive power
Data Source
AI summary
The objective optical system includes in order from an object side, a first unit having a positive refractive power, a second unit having a negative refractive power, and a third unit having a positive refractive power, and focusing is carried out by moving the second unit, the first unit and the third unit are fixed at the time of focusing, and the first unit G1 includes in order from the object side, a negative lens L1, one of a positive lens and a cemented lens, and a positive lens, and the third unit includes a positive lens, and a cemented lens of a positive lens and a negative lens, and the objective optical system satisfies the following conditional expression (3)−20<f2/f<−5 (3)where,f2 denotes a focal length of the second unit, andf denotes a focal length of the overall objective optical system in a normal observation state.