Anamorphic Objective Zoom Lens Design for Oval Bokeh
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Solution Overview
Problem
Anamorphic objective zoom lenses face challenges in achieving a compact diameter with a useful zoom range from wide to narrow fields of view while minimizing residual optical aberrations and maintaining the desired artistic bokeh and depth of field characteristics, especially with the advent of digital cameras which are less tolerant of chromatic aberration and field curvature.
Innovation Solution
The design incorporates a negatively powered spherical first lens group, an anamorphic second lens group with cylindrical surfaces, a positively powered spherical third lens group, a variable power spherical fourth lens group for zooming, and a positively powered spherical fifth lens group with an optical stop, allowing for high aberration correction and low breathing, while maintaining the traditional oval bokeh and different depths of field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a rear anamorphic lens group configuration is used, then the lens structure is simpler and more common, but the bokeh becomes spherical instead of oval and the aperture may be slow
Solution Approach 1:
The patent inverts the conventional arrangement by placing the anamorphic lens group at the front instead of the rear. This inversion allows the cylindrical surfaces to be positioned where they can properly shape the light cones to produce oval bokeh, while still maintaining a manageable overall structure through the specific configuration of five lens groups.
Solution Approach 2:
The patent introduces spherical lens groups with specific powers (positive and negative) as intermediaries between the front anamorphic group and the image plane. These intermediary spherical groups help control the light paths and aberrations, enabling the system to achieve both oval bokeh and acceptable aperture performance.
2Object-generated harmful factors
If a front anamorphic lens group configuration is used, then oval bokeh is achieved, but the lens becomes large in diameter with higher weight and cost
Solution Approach 1:
The patent divides the lens system into five distinct lens groups with specific functions: a front anamorphic group for oval bokeh, followed by spherical groups with alternating positive and negative powers. This segmentation allows each group to be optimized for its specific function, reducing the overall size and weight compared to a single large anamorphic system.
Solution Approach 2:
The patent employs spherical lens groups with variable powers (positive and negative) to adjust the optical parameters of the system. By changing the power parameters of these spherical groups, the design achieves compact dimensions while maintaining the oval bokeh characteristic produced by the front anamorphic group.
3Object-generated harmful factors
If front anamorphic zoom lenses with small zoom ratios are used, then oval bokeh is maintained, but the field of view range is limited and the lens remains large
Solution Approach 1:
The patent implements a zoom mechanism that allows dynamic adjustment of the focal length by moving the lens groups relative to each other. The variable power spherical zoom group enables continuous change in the field of view from wide to narrow angles while maintaining the anamorphic compression and oval bokeh characteristics throughout the zoom range.
Solution Approach 2:
The patent designs a multi-functional lens system where the front anamorphic group serves multiple purposes: it creates oval bokeh, provides anamorphic compression for cinematic aspect ratios, and works in conjunction with the spherical groups to achieve a useful zoom range. This universal design allows a single lens to replace multiple specialized lenses.
4Productivity
If conventional anamorphic zoom lenses are used, then zoom functionality is provided, but residual chromatic aberration and field curvature become problematic with digital cameras
Solution Approach 1:
The patent uses the residual aberrations that traditionally were considered harmful and accepted in film-based systems as part of the artistic anamorphic look. By carefully controlling and balancing these aberrations through the specific configuration of spherical and anamorphic groups, the design converts what would be defects into characteristic features that are now acceptable or even desirable in digital cinema, while minimizing excessive chromatic aberration through the spherical 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
This configuration results in a compact anamorphic objective zoom lens with reduced residual chromatic aberration, efficient telecentric light paths, and a medium fast full aperture, providing a balanced blend of optical performance and artistic characteristics suitable for both film and digital cameras.
Implementation Method 1
an anamorphic second lens group with at least one cylindrical surface in a first direction and at least one other cylindrical surface in a substantially perpendicular direction to the first direction
Implementation Method 2
a variable power spherical zoom fourth lens group and a positive (+) power spherical fifth lens group wherein an aperture stop is located before, after or preferably within the spherical fifth power lens group
Data Source
AI summary
The anamorphic objective zoom lens includes, along an optical axis and in order from an object space to an image space: at least a negative (−) power spherical first lens group; an anamorphic second lens group, spherical third lens group preferably having positive (+) power, a variable power spherical fourth lens group and a positive (+) power spherical fifth lens group. The aperture stop is located before, after or preferably within the spherical fifth lens group. All spherical lens groups contain spherical and plano refractive optical surfaces. The anamorphic second lens group contains cylindrical and plano optical surfaces with at least one cylindrical surface oriented at substantially 90 degrees about at least one other cylindrical surface. The spherical first lens group may provide focusing. The variable power spherical fourth lens group provides zooming.