Zoom Lens Chromatic Aberration Correction via Fourth Unit
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Solution Overview
Problem
Existing zoom lenses with high zooming ratios face challenges in maintaining high optical performance across the entire zoom range due to increased variations in aberrations, particularly chromatic aberration, which is difficult to correct without appropriate configuration of the fourth lens unit.
Innovation Solution
A zoom lens configuration that includes a first lens unit with positive refractive power for focusing, a second lens unit with negative refractive power for zooming, a third lens unit with positive or negative refractive power for compensating zooming variations, and a fourth lens unit with positive refractive power that does not move, along with an aperture stop, to correct chromatic aberrations by optimizing the incidence heights and refractive powers of lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a high zooming ratio is achieved in a positive-lead type four-unit zoom lens, then the zooming capability is improved, but chromatic aberration (lateral and axial) increases and optical performance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Abbe constant of the positive lens in the fourth lens unit to be within 20 < νd < 60, and setting the focal length ratio f3/f4 within 0.3 < f3/f4 < 1.0. These parameter optimizations enable the lens to maintain high optical performance across the entire zoom range while achieving a high zooming ratio of 3.0x or more.
Solution Approach 2:
The patent applies local quality by specifically optimizing the fourth lens unit (which has positive refractive power and does not move during zooming) with particular attention to the Abbe constant of its positive lens. This localized optimization of the rearmost lens unit enables effective correction of chromatic aberration across the entire zoom range, resolving the contradiction between high zooming ratio and optical performance.
2Ease of manufacture
If the fourth lens unit is not appropriately configured, then manufacturing is simplified, but chromatic aberration correction becomes difficult and optical performance decreases
Solution Approach 1:
The patent establishes specific parameter ranges for the fourth lens unit: the Abbe constant νd of the positive lens should be 20 < νd < 60, and the focal length ratio f3/f4 should satisfy 0.3 < f3/f4 < 1.0. These parameter specifications provide clear manufacturing guidelines that balance ease of production with effective chromatic aberration correction.
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 effectively corrects chromatic aberrations across the entire zoom range, ensuring high optical performance from wide angle to telephoto ends, by strategically arranging lenses with specific refractive powers and Abbe constants, thereby maintaining a well-balanced correction of secondary spectra.
Implementation Method 1
a fourth lens unit for imaging, which has a positive refractive power
Implementation Method 2
a zoom lens which employs an optical material having anomalous dispersibility, adequately corrects chromatic aberration
Data Source
Figure 1~2
Figure 3
Figure 4A~4B
AI summary
An object of the present invention is to provide a zoom lens which has a high zooming ratio, adequately corrects chromatic aberration in an entire zoom range from a wide angle end to a telephoto end, and has a high optical performance in the entire zoom range. The zoom lens according to the present invention includes in order from an object side to an image side: a first lens unit; a second lens unit; a third lens unit; an aperture stop; and a fourth lens unit; wherein a partial dispersion ratio θLm of a material of a positive lens Lm formed of a material having a highest partial dispersion ratio, which is contained in a rear group, a distance d from the aperture stop to an image plane, a distance dLm from the aperture stop to a positive lens Lm, an average value νRfp of Abbe constants of materials of positive lenses contained in a front group, an average value θRfp of partial dispersion ratios thereof, an average value vRfn of Abbe constants of materials of negative lenses contained in the front group, and an average value θRfn of partial dispersion ratios thereof are each appropriately set.