Zoom Lens n-th Unit Abbe Number Refractive Index Design
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Solution Overview
Problem
Existing zoom lenses face challenges in achieving a short total length, small size, high aperture ratio, and satisfactory correction of chromatic aberration across the entire zoom range, particularly at the telephoto end, due to increased axial chromatic aberration and system size issues.
Innovation Solution
A zoom lens configuration with a first positive refractive power unit, an intermediate lens group with negative refractive power, and an n-th lens unit with specific refractive index and Abbe number conditions, where the interval between the (n−1)th and n-th lens units is smaller at the telephoto end, and the n-th lens unit includes low dispersion material positive lenses and a high refractive index lens on the image side, optimizing the lens configuration to reduce axial chromatic aberration and Petzval sum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If refractive powers of lens units are increased to downsize the zoom lens, then the total length and system size are reduced, but axial chromatic aberration is generated and increased, particularly at the telephoto end
Solution Approach 1:
The patent applies parameter changes by precisely controlling the refractive index (Nd) and Abbe number (νd) of lens materials, as well as the interval between lens units during zooming. By setting specific parameter ranges for the n-th lens unit (Nd: 1.84-2.20, νd: 65.0-97.0) and adjusting the interval between (n-1)-th and n-th lens units, the patent achieves downsizing while correcting axial chromatic aberration through material parameter optimization
Solution Approach 2:
The patent uses composite material principles by combining multiple lens units with different material properties in the n-th lens unit. Specifically, it combines positive lenses made of low dispersion material (high Abbe number) with a positive lens made of high refractive index material, creating a composite lens system that simultaneously reduces chromatic aberration and enables compact design
2Object-generated harmful factors
If the lens configuration of the fourth lens unit is not appropriately set, then the entire system size is increased in achieving a large aperture, but if appropriately set, chromatic aberration correction and optical performance are improved
Solution Approach 1:
The patent applies local quality by giving the n-th lens unit (fourth lens unit) specific local characteristics different from other lens units. The n-th lens unit is configured with particular material properties (Nd: 1.84-2.20, νd: 65.0-97.0) and structural parameters (tn/skw ratio: 1.1-10.0) that are optimized specifically for this position in the lens system, enabling it to correct chromatic aberration while maintaining compact overall size
3Illumination intensity
If refractive powers are increased to secure high aperture ratio, then aperture ratio is improved, but variation in chromatic aberration accompanying zooming is increased
Solution Approach 1:
The patent applies dynamics by making the interval between the (n-1)-th and n-th lens units variable during zooming, rather than fixed. This dynamic adjustment of the interval allows the lens system to maintain proper optical compensation across different zoom positions, reducing variation in chromatic aberration while preserving high aperture ratio capability
Solution Approach 2:
The patent implements feedback through the interdependent relationship between the movable first lens unit and the specifically configured n-th lens unit. As the first lens unit moves during zooming to change focal length, the interval between (n-1)-th and n-th lens units is also adjusted in response, creating a feedback mechanism that continuously optimizes chromatic aberration correction across the zoom range
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 enables a compact zoom lens with a large aperture while effectively correcting chromatic aberration and reducing astigmatism variation, achieving high optical performance across the entire zoom range.
Implementation Method 1
the n-th lens unit includes a plurality of positive lenses LPL made of a material that satisfies the following conditional expression: 65.0d97.0, where νd is an Abbe number of the material of the plurality of positive lenses LPL, wherein the n-th lens unit includes a positive lens LPH arranged on the image side of the plurality of positive lenses LPL and made of a material that satisfies the following conditional expression: 1.84Nd2.20, where Nd is a refractive index of the material of the positive lens LPH
Data Source
AI summary
A zoom lens includes lens units whose interval between adjacent units is changed during zooming, wherein the lens units consist of, in order from an object side, a positive first unit, an negative intermediate lens group including a unit, a positive (n−1)-th unit, and a positive n-th unit, wherein the first unit moves during zooming, wherein an interval between the (n−1)-th and n-th units is smaller at telephoto end than at wide angle end, wherein the n-th unit includes positive lenses LPL made of a material having proper Abbe number, wherein the n-th lens unit includes a positive lens LPH arranged on the image side of the lenses LPL and made of a material having proper refractive index and wherein a distance between lens surfaces on the most-object side and on the most-image side of the n-th lens unit, and back focus at the wide angle end are properly set.