Objective Optical System for Endoscope Focusing
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Solution Overview
Problem
Surgical endoscopes face challenges in achieving high image quality for stereoscopic observation while maintaining the endoscope's outer diameter and depth of field, as reducing pixel pitch narrows the depth of field and increasing F-number degrades contrast.
Innovation Solution
An objective optical system comprising a front group, an intermediate group, and a rear group, where focusing is achieved by varying the focal length by moving the intermediate group along the optical axis, with specific conditional expressions ensuring optimal lateral magnifications and focal length ratios to maintain image quality and reduce vertical shift of images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel pitch of the image sensor is made small to achieve high image quality, then the depth of field becomes narrow
Solution Approach 1:
The patent applies the dynamics principle by making the intermediate group movable along the optical axis to enable focusing between far-point and near-point observation states. This dynamic adjustment allows the system to maintain adequate depth of field for small pixel pitch sensors by actively changing the optical configuration to accommodate different object distances, thereby resolving the contradiction between small pixel pitch and sufficient depth of field.
2Reliability
If the F-number is made large to maintain the depth of field, then the contrast is degraded
Solution Approach 1:
The patent resolves this contradiction by dynamically adjusting the focal length through movement of the intermediate group rather than relying on a large F-number. This allows the system to maintain both adequate depth of field and good contrast by actively adapting the optical parameters to the observation requirements, avoiding the need to increase the F-number which would degrade contrast.
3Adaptability or versatility
If the focal length is varied by moving the intermediate group to provide focusing function, then the vertical shift of images increases
Solution Approach 1:
The patent applies parameter changes by carefully controlling the movement distance of the intermediate group and optimizing its position to minimize vertical image shift. By precisely adjusting the focal length parameter through controlled movement of the intermediate group, the system achieves focusing functionality while keeping vertical shift within acceptable limits, thus resolving the contradiction between adaptability and manufacturing precision.
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 enables comfortable and safe stereoscopic observation with reduced vertical shift of images, achieving high image quality while maintaining a compact endoscope design and appropriate depth of field.
Implementation Method 1
the front group includes a first negative lens, and the first negative lens has a meniscus shape having an aspheric surface
Implementation Method 2
focusing is carried out from a far-point observation state to a near-point observation state by varying a focal length by moving the intermediate group along an optical axis
Data Source
AI summary
An objective optical system consists of, in order from an object side, a front group, an intermediate group, and a rear group, wherein focusing is carried out from a far-point observation state to a near-point observation state by varying a focal length by moving the intermediate group along an optical axis, and the front group includes a first negative lens, and the first negative lens has a meniscus shape having an aspheric surface, and in any of the far-point observation state and the near-point observation state, the objective optical system satisfies the following conditional expressions (1) and (2)|(½)×βf×βt×((1/βf)−1)|≤0.055 (1)0.12≤Sa/FL≤0.44 (2).