Zoom Lens Astigmatism Control via Curvature and Stop Positioning
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Solution Overview
Problem
Existing zoom lenses face challenges in maintaining optical properties and preventing astigmatism, especially at intermediate focal lengths, due to the complexity of lens groups and lack of brightness, which affects their usability and fabrication costs.
Innovation Solution
A zoom lens design comprising a first positive refracting power lens group, a second negative refracting power lens group with specific surface curvatures, and a third positive refracting power lens group, with an aperture stop between the second and third groups, allowing for coordinated movement during zooming and focusing to maintain optical quality and reduce astigmatism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the second lens group is made up of two lenses to simplify construction, then the lens is easier to manufacture and shorter in length, but it becomes difficult to maintain optical properties and astigmatism control
Solution Approach 1:
The patent applies local quality by giving specific curvature characteristics to individual lenses within the second lens group. The second negative lens has an image side surface with larger absolute paraxial curvature than the object side surface, while the third positive lens has an object side surface with larger absolute paraxial curvature than the image side surface. This localized curvature differentiation allows each lens to contribute specifically to correcting astigmatism and maintaining optical properties while keeping the overall group simple.
Solution Approach 2:
The patent uses parameter changes by establishing specific mathematical relationships between the curvatures of lens surfaces. The conditions |r2g3| < |r2g4| and |r2g4| < |r3g3| define precise parameter ranges that optimize the balance between construction simplicity and optical performance. By controlling these curvature parameters, the patent resolves the contradiction between simple two-lens construction and effective astigmatism control.
2Reliability
If the second lens group is made up of three lenses to improve optical properties, then astigmatism control improves, but the lens construction becomes more complex and length increases
Solution Approach 1:
The patent applies local quality by assigning specific functional roles to each lens within the three-lens second group. The first negative meniscus lens handles basic negative power, the second negative lens provides astigmatism correction through its specific curvature relationship (|r2g3| < |r2g4|), and the third positive lens contributes to overall focus and aberration control. This localized functional differentiation achieves effective astigmatism control while maintaining relatively simple construction.
Solution Approach 2:
The patent merges multiple functions into the second lens group by combining negative and positive lenses with specific curvature relationships. The group collectively provides negative refracting power, astigmatism correction, and focus adjustment, reducing the need for separate dedicated components and thereby managing overall system complexity while achieving reliable optical performance.
3Reliability
If the aperture stop is positioned to control brightness and reduce astigmatism, then optical quality improves, but the first lens group diameter must increase
Solution Approach 1:
The patent applies preliminary action by positioning the aperture stop between the second and third lens groups, before the light rays converge to the image plane. This early placement of the stop allows it to effectively control the chief rays and reduce astigmatism before the rays fully converge, improving optical quality without requiring excessive lens group diameters. The stop's position is optimized to achieve astigmatism control with minimal impact on the first lens group size.
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 design achieves a simplified construction, reduces astigmatism fluctuations, and ensures a fast zoom lens with the desired angle of view and zoom ratio, while maintaining optical clarity and balancing aberrations across the zoom range.
Implementation Method 1
a first lens group of positive refracting power, a second lens group of negative refracting power and a third lens group of positive refracting power
Data Source
AI summary
The invention relates to a zoom lens which, albeit being of simplified construction, makes sure brightness and holds back fluctuations of astigmatism, and facilitates making sure being fast and the angle of view and the zoom ratio at the wide-angle end. The zoom lens comprises a first group G1 of positive power, a second group G2 of negative power and a third group G3 of positive power, with a stop S between the second group G2 and the third group G3. Upon zooming from the wide-angle end to the telephoto end, the first group G1, the second group G2, and the third group G3 moves; the second group G2 moves toward the object side after moving toward the image side; the first group G1 and the third group G3 are positioned on the object side at the telephoto end with respect to the wide-angle end. The first group G1 comprises one negative lens and one or two positive lenses, and the second group G2 comprises a first negative meniscus lens convex on its object side, a second negative lens wherein the image side surface is larger in the absolute value of a curvature than the object side surface, and a third positive lens wherein the object side surface is larger in the absolute value of a curvature than the image side surface. Upon focusing from a far distance to a near distance, the second group G2 moves.