Telephoto Optical System with Moving Focus and Negative Lens Unit
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Solution Overview
Problem
Existing telephoto optical systems face challenges in achieving a long focal length, small F-number, and reduced size and weight while effectively correcting aberrations, particularly chromatic aberration, due to increased lens diameter and weight with a large aperture.
Innovation Solution
The optical system is configured with a first lens unit having positive refractive power, a second lens unit moving in focusing, and a third lens unit with negative refractive power, adhering to specific conditional inequalities to optimize lens distances and thicknesses, allowing for aberration correction and size/weight reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the telephoto optical system is configured to have a large aperture (small F-number), then the light gathering ability and imaging performance are improved, but the effective diameter of the lens on the object side is increased, making it difficult to achieve reduction in size and weight
Solution Approach 1:
The optical system is divided into multiple lens units (first, second, and third lens units) with different refractive powers and functions. The first lens unit has positive refractive power, the second has positive or negative refractive power for focusing, and the third has negative refractive power. This segmentation allows each unit to be optimized independently, enabling the system to achieve large aperture while controlling the effective diameter of individual lenses to manage weight.
Solution Approach 2:
Different lens units are assigned different local optical properties: the first lens unit provides positive convergence, the second enables focusing movement, and the third provides negative divergence. The third lens unit specifically uses negative refractive power to reduce the effective diameter requirement of front lenses while maintaining overall system performance, thus addressing the weight issue locally without compromising global light gathering ability.
2Illumination intensity
If the telephoto optical system is configured to have a large aperture, then the imaging performance is improved, but the effective diameter of the lens on the object side is increased, making it difficult to achieve reduction in size
Solution Approach 1:
The optical system is divided into multiple lens units (first, second, and third lens units) with different refractive powers and functions. The first lens unit has positive refractive power, the second has positive or negative refractive power for focusing, and the third has negative refractive power. This segmentation allows each unit to be optimized independently, enabling the system to achieve large aperture while controlling the effective diameter of individual lenses to manage weight.
Solution Approach 2:
Different lens units are assigned different local optical properties: the first lens unit provides positive convergence, the second enables focusing movement, and the third provides negative divergence. The third lens unit specifically uses negative refractive power to reduce the effective diameter requirement of front lenses while maintaining overall system performance, thus addressing the weight issue locally without compromising global light gathering ability.
3Length of moving object
If the telephoto optical system is designed with long focal length, then the telephoto performance is achieved, but the lens diameter and weight are increased
Solution Approach 1:
The optical system is divided into multiple lens units (first, second, and third lens units) with different refractive powers and functions. The first lens unit has positive refractive power, the second has positive or negative refractive power for focusing, and the third has negative refractive power. This segmentation allows each unit to be optimized independently, enabling the system to achieve large aperture while controlling the effective diameter of individual lenses to manage weight.
Solution Approach 2:
The patent applies specific conditional inequalities to control the optical parameters: 0.10 < TL3/TL < 0.40 for the ratio of third lens unit length to total length, and 0.70 < SD3/TL3 < 1.30 for the ratio of sum of lens thicknesses to third lens unit length. These parameter constraints optimize the balance between focal length, aperture, and lens dimensions to reduce weight while maintaining telephoto performance.
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 satisfactory aberration correction and reduces size and weight by strategically arranging lenses in the third lens unit, meeting the demands for telephoto performance.
Implementation Method 1
a first lens unit having positive refractive power
Implementation Method 2
a second lens unit having positive or negative refractive power and configured to move in focusing
Implementation Method 3
a third lens unit having negative refractive power
Data Source
AI summary
An optical system includes a first unit having positive refractive power, a second unit having positive or negative refractive power and configured to move in focusing, and a third unit having negative refractive power in order from an object side to an image side. A distance between adjacent two of the units changes in focusing. When a distance on an optical axis from a lens surface closest to the object side to a lens surface closest to the image side is TL, a distance on the optical axis from a lens surface closest to the object side to a lens surface closest to the image side in the third unit is TL3, a sum of thicknesses, on the optical axis, of lenses in the third unit is SD3, and the largest of the thicknesses of the lenses in the third unit is DM3, the optical system satisfies predetermined conditional inequalities.