Fixed Focus Lens with Single Negative Focusing Group
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Solution Overview
Problem
Conventional fixed focus lenses for mirror-less single lens cameras do not achieve sufficient size and weight reductions due to limitations in optical system design, including large front element diameters and insufficient focusing sensitivity, which hinder further size reductions in recent camera designs.
Innovation Solution
A fixed focus lens configuration comprising a first lens group with positive and negative lenses, a second lens group with a single negative lens element, and a third lens group, where the first lens group is fixed and includes an aperture stop, and the second lens group moves along the optical axis for focusing, optimizing aberration correction and reducing the overall length of the optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the focusing lens group is configured by one negative lens and disposed farther on the object side than the diaphragm, then the focusing stroke is shortened, but the front element diameter becomes larger
Solution Approach 1:
The lens is divided into multiple groups: a first lens group (positive power) containing the diaphragm, and a second lens group (negative power) for focusing. This segmentation allows the focusing group to be positioned closer to the image plane rather than the object side, reducing the front element diameter while maintaining effective focusing stroke.
Solution Approach 2:
Instead of placing the negative power focusing lens group on the object side of the diaphragm (conventional approach), this patent inverts the arrangement by placing it on the image plane side. This inversion resolves the contradiction by allowing short focusing stroke without requiring a large front element diameter.
2Measurement precision
If the focusing group is moved greatly to capture images at minimum object distance, then the focusing sensitivity is improved, but the size of the optical system increases
Solution Approach 1:
The patent optimizes the optical parameters of the lens groups, specifically setting the focal length of the second lens group (|F2|) to be 0.35-0.65 times the focal length of the first lens group (F1). This parameter optimization achieves high focusing sensitivity with minimal movement distance, reducing the overall optical system size.
3Reliability
If multiple lens elements are used in the focusing group, then the aberration correction is improved, but the device complexity increases
Solution Approach 1:
The patent extracts the aberration correction function from the focusing group and places it in the first lens group (which contains the diaphragm and positive power lenses). The second lens group is simplified to contain only one or two negative lenses for focusing, reducing complexity while maintaining overall aberration correction capability.
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, lightweight lens with improved imaging performance and reduced size, allowing for shorter optical system lengths while effectively correcting various types of aberrations and minimizing the front element diameter.
Implementation Method 1
a first lens group (G11) having a positive refractive power; a second lens group (G12) having a negative refractive power; and a third lens group (G13) having a positive refractive power
Data Source
AI summary
A fixed focus lens comprising, sequentially from an object side, a first lens group having a positive refractive power; a second lens group having a negative refractive power; and a third lens group having a positive refractive power. The first lens group includes an aperture stop. The second lens group is configured by a single lens element. During focusing, the second lens group moves along an optical axis and the first lens group and the third lens group are fixed with respect to an imaging plane.