Zoom Lens with Fixed Front Unit for Compact High-Ratio Design
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Solution Overview
Problem
Conventional zoom lenses face challenges in achieving a wide angle of view with high optical performance and downsizing while maintaining a small F-number, leading to increased size and aberration variations, particularly in achieving a long back focus and high zoom ratio.
Innovation Solution
A zoom lens configuration with a front lens unit having a positive refractive power that does not move during zooming, an Nf lens unit with negative refractive power, and rear lens units that move during zooming, along with a specific refractive power arrangement and conditional expressions to control the movement and positioning of lens units, ensuring a short entrance pupil and suppressing the increase in front lens diameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a zoom lens is designed with a wide angle of view and high zoom ratio, then the magnification-varying ratio is improved, but the front lens diameter and overall size increase significantly
Solution Approach 1:
The zoom lens is divided into multiple lens units (first through fifth lens units) with different refractive powers and movement characteristics. The first lens unit has positive refractive power and remains fixed during zooming, while subsequent units move to achieve magnification variation. This segmentation allows the front lens diameter to be determined by the fixed first unit rather than the entire zoom mechanism, resolving the contradiction between high zoom ratio and small front lens diameter.
Solution Approach 2:
Instead of having the front lens unit move during zooming (conventional approach), this invention keeps the first lens unit fixed and uses rear lens units for magnification variation. This inverted approach allows the front lens diameter to remain small while still achieving wide angle of view and high zoom ratio through the movement of subsequent lens units.
2Illumination intensity
If the F-number is made small to improve brightness, then light transmission is improved, but aberration variations increase and optical performance deteriorates
Solution Approach 1:
Different lens units are assigned specific refractive powers and movement characteristics optimized for their local functions. The first lens unit has positive refractive power for wide angle coverage, while subsequent units have alternating positive and negative powers for aberration correction during zooming. This local optimization allows small F-number operation while maintaining aberration correction through coordinated movement of units with different optical properties.
Solution Approach 2:
The invention changes the refractive powers and movement distances of different lens units according to specific conditional expressions. By optimizing parameters such as the refractive power of the first lens unit relative to the wide-angle focal length, and the movement distances of subsequent units, the system achieves small F-number operation with controlled aberration variations across the zoom range.
3Reliability
If the back focus is extended to improve image quality, then the image plane distance is improved, but the overall lens length and complexity increase
Solution Approach 1:
The invention uses dynamic movement of the second through fifth lens units during zooming to achieve both extended back focus and compact overall length. The fifth lens unit, positioned closest to the image plane, moves to adjust the back focus distance, while the coordinated movement of intermediate units maintains the optical path length within compact dimensions. This dynamic adjustment allows long back focus for image quality while keeping the stationary lens barrel compact.
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 a compact, high-performance zoom lens with a long back focus, high zoom ratio, and small F-number, effectively correcting various aberrations across the zoom range and maintaining optical quality.
Implementation Method 1
a zoom lens includes, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power
Data Source
Figure 1~2
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Figure 5~6
AI summary
A zoom lens, includes, in order from object side: a front unit including a unit including a first unit arranged closest to the object side and not moving for zooming; an Nf unit including three or more lenses and having a negative refractive power; an stop; a first rear unit moving during zooming; a second rear unit moving during zooming; and a third rear unit not moving for zooming, in which: the front unit includes four or more lenses and includes one or more units having a positive refractive power; and a difference between positions of the first rear unit at a wide angle end and a telephoto end, a difference between positions of the second rear unit at the wide angle end and the telephoto end, a focal length of the second rear unit, and a focal length of the zoom at the wide angle end are appropriately set.