Six-Lens Endoscope Objective With Cemented Pairs for Wide-Angle Correction
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Solution Overview
Problem
Existing endoscope objective optical systems struggle to provide a larger angle of view while satisfactorily correcting various aberrations, including chromatic aberration.
Innovation Solution
An objective optical system for an endoscope comprising a front group with negative focal power and a rear group with positive focal power, where specific lenses are cemented together, adhering to certain focal length ratios and conditions to balance power and correct aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the angle of view is increased, then the field of observation is improved, but various aberrations including chromatic aberration become more difficult to correct
Solution Approach 1:
The objective optical system is divided into a front group with negative focal power and a rear group with positive focal power. The front group includes three lenses (first negative, second negative, third positive) and the rear group includes three lenses (fourth positive, fifth positive, sixth negative). This segmentation allows each group to independently address specific aberrations while collectively achieving a wide angle of view of 155 degrees or more with satisfactory correction of various aberrations including chromatic aberration.
Solution Approach 2:
The patent employs cemented lens combinations where the second lens and third lens are cemented together, and the fifth lens and sixth lens are cemented together. These composite lens structures use materials with different refractive indices and Abbe numbers to correct chromatic aberrations. Specifically, the cemented lenses are designed with refractive index differences (Nd4-Nd5 between 0.05-0.50 and Nd5-Nd6 between 0.05-0.45) to achieve effective chromatic aberration correction while maintaining the wide angle of view.
2Manufacturing precision
If the focal length ratio between rear group and front group is optimized, then aberration correction is improved, but the angle of view may be limited
Solution Approach 1:
The patent establishes specific parameter ranges for the focal length ratio between the rear group and front group. Conditional expression (1) specifies that the absolute value of the ratio of the focal length of the rear group to the focal length of the front group should be within a specific range. This parameter optimization ensures that the wide angle of view of 155 degrees or more is achieved while maintaining satisfactory correction of various aberrations including chromatic aberration.
3Manufacturing precision
If cemented lenses are used, then chromatic aberration correction is improved, but manufacturing complexity increases
Solution Approach 1:
The patent uses cemented lens combinations where the second lens and third lens are cemented together, and the fifth lens and sixth lens are cemented together. These composite structures are designed with controlled refractive index differences to achieve effective chromatic aberration correction. The cemented lens design, while adding manufacturing steps, provides superior optical performance by eliminating air gaps and enabling precise chromatic aberration control through material selection.
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 wider angle of view while effectively suppressing distortion, field curvature, and chromatic aberrations, enhancing image quality for medical observations.
Implementation Method 1
An objective optical system for an endoscope consists of, in order from an object side toward an image side, a front group having negative focal power, an aperture stop, and a rear group having positive focal power
Implementation Method 2
the second lens and the third lens are cemented to each other; and the fifth lens and the sixth lens are cemented to each other
Data Source
AI summary
An objective optical system for an endoscope consisting of, in order from an object side toward an image side: a front group having negative focal power; an aperture stop; and a rear group having positive focal power, wherein: the front group includes only three lenses, which consist of, in order from the object side toward the image side: a first lens having negative focal power; a second lens having negative focal power; and a third lens having positive focal power, the rear group includes only three lenses, which consist of, in order from the object side toward the image side: a fourth lens having positive focal power; a fifth lens having positive focal power; and a sixth lens having negative focal power, the second lens and the third lens are cemented to each other, and the fifth lens and the sixth lens are cemented to each other.