Endoscope Objective Lens Aberration Correction
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Solution Overview
Problem
Current endoscope objective lenses have limitations in achieving high image quality with high-pixel CCDs due to insufficient correction of magnification chromatic aberration, field curvature, and a narrow viewing angle, while also being unsuitable for size reduction and patient comfort.
Innovation Solution
An endoscope objective optical system with a retrofocus configuration using a small number of lenses, specifically a first group with a negative plano-concave lens and a second group with a combined positive and negative lens, satisfying specific conditional expressions for focal lengths, radii of curvature, and power arrangements to correct aberrations and achieve a wide viewing angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-pixel CCD is used to enhance image quality, then measurement precision is improved, but manufacturing precision requirements increase due to the need for better aberration correction
Solution Approach 1:
The objective lens is divided into multiple lens groups (first through fourth lens groups) with specific positive and negative powers. Each group is assigned specific functions: the first and second groups primarily correct magnification chromatic aberration, while the third and fourth groups correct field curvature. This segmentation allows each component to be optimized for its specific function, achieving high overall image quality suitable for high-pixel CCDs.
Solution Approach 2:
Different regions of the optical system are designed with different optical properties. The patent specifies different refractive indices and Abbe numbers for different lens groups (e.g., first lens group with Nd=1.888, Vd=40.76; second lens group with Nd=1.69, Vd=54.01). This local differentiation of optical materials allows precise control over chromatic aberration and field curvature in different parts of the system, meeting the high manufacturing precision requirements.
2Adaptability or versatility
If the viewing angle is increased to find lesion sites, then adaptability is improved, but device complexity increases due to the need for more lenses
Solution Approach 1:
The patent employs a retrofocus-type configuration where the first lens group has negative power and the second lens group has positive power. This dynamic arrangement allows the optical system to achieve a wide angle of view (140° or more) while maintaining a compact structure. The specific power distribution and focal length relationships enable the system to expand the viewing angle without proportionally increasing the number of lenses.
Solution Approach 2:
The patent achieves wide-angle performance by carefully controlling key parameters: the ratio of focal lengths between lens groups, the radii of curvature of specific surfaces, and the refractive indices of lens materials. By optimizing these parameters within specific ranges, the system achieves 140° or more viewing angle with only four lens groups, avoiding unnecessary complexity.
3Volume of moving object
If the lens size is reduced to reduce patient burden, then volume is improved, but manufacturing precision worsens due to tighter tolerances
Solution Approach 1:
The patent achieves compact lens size by nesting the four lens groups in a condensed arrangement along the optical axis. The specific configuration allows the groups to be closely spaced while maintaining proper optical function. The total length is controlled by optimizing the air gaps and thicknesses between lens groups, creating a compact structure that minimizes patient burden.
Solution Approach 2:
The patent uses a retrofocus configuration that changes the traditional dimensional arrangement of lenses. By positioning the negative power first lens group closer to the object and the positive power second lens group further back, the system achieves compact axial length while maintaining wide angle of view. This dimensional reorganization allows small size without sacrificing optical performance or requiring excessive manufacturing tolerances.
4Device complexity
If the number of lenses is reduced to simplify the structure, then device complexity is improved, but manufacturing precision worsens due to difficulty in correcting aberrations
Solution Approach 1:
The patent divides the optical system into four functional lens groups with specific positive and negative powers. This segmentation into minimal necessary components allows correction of both magnification chromatic aberration and field curvature with only four groups, achieving structure simplicity while maintaining adequate aberration correction capability for high-pixel imaging.
Solution Approach 2:
Each lens group is designed to serve multiple functions simultaneously. For example, the first lens group with negative power contributes to both wide-angle performance and magnification chromatic aberration correction, while the second lens group with positive power aids in both focusing and field curvature correction. This multi-functionality allows adequate aberration correction with minimal lens groups, simplifying the overall structure.
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 provides satisfactory aberration correction and a wide viewing angle while maintaining a compact size, ensuring compatibility with high-pixel imaging devices and reducing patient burden.
Implementation Method 1
a first group, an aperture stop, and a second group, wherein the first group has positive power and is constituted of a negative first lens whose surface on the object side is flat and a positive second lens
Implementation Method 2
the second group has positive power and is constituted of a combined lens formed of a positive third lens and a negative fourth lens
Data Source
Figure 1
Figure 2
Figure 3(a)~3(d)
AI summary
Provided is an endoscope objective optical system (1) that is constituted of, in order from an object side, a positive first group (G1), an aperture stop (S), and a positive second group (G2), wherein the first group (G1) is constituted of a negative first lens (L1) whose surface on the object side is flat and a positive second lens (L2); the second group (G2) is constituted of a combined lens (L34) formed of a positive third lens (L3) and a negative fourth lens (L4); and Conditional Expressions (1) to (3) are satisfied. f31, F32, and f are the focal lengths of the third lens, the fourth lens, and an entire system, respectively; and R3 and R4 are the radii of curvature of an object-side surface and an image-side surface of the second lens, respectively. 1.2 < f31/f < 1.55...(1), -2.8 < f32/f < -1.98...(2), and 0.38 < |R4+R3|/|R4-R3| < 0.77...(3).