Zoom Lens Aberration Correction via Moving Lens Groups
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Solution Overview
Problem
Conventional zoom lenses for surveillance cameras have insufficient correction of spherical aberration and longitudinal chromatic aberration at the telephoto end, and insufficient zoom ratios, which affect image quality and versatility.
Innovation Solution
A zoom lens configuration with a first positive refractive power lens group, a second negative refractive power lens group, a third positive refractive power lens group, and a fourth lens group, where the first and fourth lens groups remain stationary, and the second and third lens groups move to adjust their spacing, satisfying specific conditional expressions to correct spherical and chromatic aberrations effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional zoom lens configuration is used, then the structure is simple, but spherical aberration and longitudinal chromatic aberration at the telephoto end cannot be sufficiently corrected
Solution Approach 1:
The first lens group is segmented into four distinct lenses (L1-L4) with specific refractive powers and shapes. This segmentation allows independent optimization of each lens to correct different types of aberrations, particularly spherical and longitudinal chromatic aberration at the telephoto end, while maintaining a manageable overall structure.
Solution Approach 2:
Each lens within the first lens group is assigned specific local properties: L1 has negative refractive power with meniscus shape convex toward object side, L2 and L3 have positive refractive power, and L4 has negative refractive power. This local quality differentiation enables targeted correction of optical aberrations in specific regions of the lens system.
2Adaptability or versatility
If a high zoom ratio is achieved, then versatility for surveillance applications is improved, but image quality at the telephoto end deteriorates due to insufficient aberration correction
Solution Approach 1:
The lens system employs dynamic zooming capability where the second and third lens groups move relative to each other along the optical axis while the first and fourth lens groups remain stationary. This dynamic configuration enables high zoom ratio (40 times or more) while maintaining aberration correction through the specifically designed first lens group that compensates for optical distortions at various focal lengths.
3Manufacturing precision
If the first lens group consists of multiple lenses with specific configurations, then aberration correction is improved, but the lens system size increases
Solution Approach 1:
Multiple lens functions are merged into a compact first lens group where four lenses (L1-L4) with alternating refractive powers are closely arranged. This merging achieves comprehensive aberration correction (spherical and longitudinal chromatic) while minimizing the overall lens system volume through efficient spatial arrangement and stationary positioning of the first and fourth lens groups.
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 configuration achieves satisfactory correction of spherical and longitudinal chromatic aberrations at the telephoto end with a high zoom ratio, enhancing optical performance and image quality while maintaining a compact size suitable for surveillance applications.
Implementation Method 1
a first lens group that has a positive refractive power... The first lens group consists of, in order from the object side, a cemented lens that is formed by cementing a first lens, which has a negative refractive power and has a meniscus shape convex toward the object side, and a second lens which has a positive refractive power, a third lens that has a positive refractive power, and a fourth lens that has a negative refractive power
Data Source
AI summary
The zoom lens includes, in order from an object side, a positive first lens group G1, a negative second lens group G2, a positive third lens group G3, a diaphragm, and a fourth lens group G4. During zooming, only the second lens group G2 and the third lens group G3 move. The first lens group G1 includes, in order from the object side, a cemented lens that is formed by cementing a positive lens and a negative meniscus lens convex toward the object side, a positive lens, and a negative lens. A conditional expression (1): −0.8<f1a/f1b<0 is satisfied, where f1a is a composite focal length of the first to third lenses from the object side of the first lens group G1, and f1b is a focal length of the fourth lens.