Endoscope Optical System Shading Reduction
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Solution Overview
Problem
Electronic endoscopes with megapixel image pick-up devices face significant shading issues due to large incident angles, leading to a shortage of peripheral light, which existing designs struggle to address effectively, especially in maintaining optical performance and small diameter requirements.
Innovation Solution
The endoscope optical system is designed with a specific configuration including a front group with a negative and positive lens, and a rear group with a positive lens and cemented lens, optimizing focal lengths and exit pupil distance to suppress shading and maintain a wide field angle, while ensuring the system can be mounted on a small-diameter endoscope.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the endoscope optical system is designed with a short exit pupil distance to decrease the diameter of the endoscope, then the endoscope diameter is reduced, but the incident angle of light rays increases causing severe shading and peripheral light shortage
Solution Approach 1:
The patent applies parameter changes by optimizing the focal lengths of individual lens groups (front group focal length f1, rear group focal length f2, cemented lens focal length fc) and their relative positions to achieve a balanced exit pupil distance. This allows the system to maintain adequate light angles for megapixel sensors while keeping the overall endoscope diameter small, resolving the contradiction between compact size and peripheral illumination.
2Measurement precision
If the endoscope optical system uses a megapixel image pick-up device with small pixel size, then the image resolution is improved, but the photo acceptance efficiency decreases leading to increased shading
Solution Approach 1:
The patent applies local quality by designing the optical system with specific focal length ratios for different lens groups (front group, rear group, cemented lens) to optimize light distribution across the image plane. This ensures that even the peripheral regions with large incident angles receive sufficient light for megapixel sensors, while maintaining high resolution imaging capability.
3Illumination intensity
If the endoscope optical system is designed to suppress the incident angle of light rays, then the peripheral light amount is improved, but the field angle is reduced
Solution Approach 1:
The patent applies dynamics by creating a balanced optical configuration where the focal length ratios and lens group positions can be adjusted to achieve both wide field angle and controlled incident angles. The specific ratio conditions (0.25 < f/f2 < 0.35 and 0.45 < f1/f2 < 0.55) enable the system to dynamically optimize between field coverage and light angle control for megapixel imaging.
4Illumination intensity
If the endoscope optical system is designed as a telecentric optical system to suppress incident angles, then the shading is reduced, but the diameter of the endoscope optical system increases
Solution Approach 1:
The patent applies partial action by implementing a modified telecentric design that achieves sufficient incident angle control without requiring full telecentric configuration. The focal length ratio conditions provide partial telecentricity that adequately suppresses shading for megapixel sensors while maintaining a compact optical system diameter suitable for endoscope applications.
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 effectively reduces shading, maintains optical performance for fine structure observation, and allows for a smaller endoscope diameter, even with megapixel image pick-up devices, by securing the exit pupil distance and correcting aberrations such as coma and astigmatism.
Implementation Method 1
The front group comprises a negative lens and a positive lens arranged in this order from the object side, and the rear group comprises a positive lens and a cemented lens arranged in this order from the object side
Data Source
AI summary
An endoscope optical system, including a front group and a rear group arranged in this order from an object side such that an aperture stop is arranged between the front and rear groups, wherein the front group includes a negative lens and a positive lens arranged in this order from the object side, the rear group includes a positive lens and a cemented lens arranged in this order from the object side, and when f (unit: mm) denotes a focal length of an entire endoscope optical system, EX (unit: mm) denotes a distance (which takes a minus sign on the object side with respect to an image plane) from the image plane to an exit pupil, and f2 (unit: mm) denotes a focal length of the rear group, the endoscope optical system satisfies conditions:−10<EX/f<−6 (1),and1.15<f2/f<1.35 (2).