Five-Group Imaging Optical System for Focus Breathing Control
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Solution Overview
Problem
Existing imaging lenses face challenges in achieving high image formation performance, reduction in size and weight, and suppression of focus breathing while maintaining a large aperture ratio, particularly in digital cameras with mirrorless designs.
Innovation Solution
The imaging optical system is configured with specific lens groups (G1, G2, G3, G4, G5) that remain stationary or move along the optical axis during focusing, incorporating an aperture diaphragm placement and lens group movements to satisfy conditional expressions, including positive and negative refractive powers, and using specific optical glass materials to correct chromatic aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the total length of the optical system is reduced, then the size and weight are reduced, but focus breathing increases
Solution Approach 1:
The optical system is divided into five lens groups (G1-G5) with different functions. The focus lens group is further segmented into multiple lenses (positive and negative) that can move independently during focusing, while other lens groups remain stationary. This segmentation allows precise control of focus breathing by optimizing the movement characteristics of each segment.
Solution Approach 2:
The patent optimizes specific parameters including the ratio of distances D24/LT (distance between second and fourth lens groups divided by total length), the refractive powers of individual lenses, and the movement amounts of focus lenses. By carefully controlling these parameters, the system achieves compact size while suppressing focus breathing to acceptable levels.
2Weight of moving object
If the number of lenses in the focus lens group is reduced, then the weight is reduced, but image formation performance deteriorates
Solution Approach 1:
The focus lens group uses composite lens structures including cemented lenses (positive and negative) made from different glass materials with specific refractive indices and Abbe numbers. This composite approach allows correction of chromatic aberrations and optimization of image formation performance while keeping the number of lenses minimal.
Solution Approach 2:
Different lenses within the focus group have locally optimized properties: positive lenses with specific refractive powers for focusing, negative lenses for correcting aberrations, and aspherical surfaces in specific locations for enhancing image quality. Each lens is designed with tailored characteristics rather than uniform design.
3Illumination intensity
If the aperture ratio is increased, then the amount of light is increased, but aberrations increase
Solution Approach 1:
The optical system is designed to dynamically maintain aberration correction across different aperture settings. The focus lens group's ability to move and adjust, combined with the stationary lens groups' optimized designs, ensures that aberrations remain controlled even when the aperture is opened to F1.25 or larger.
Solution Approach 2:
Specific lens groups act as intermediaries to manage aberrations. The third lens group (G3) with positive refractive power and the fifth lens group (G5) with negative refractive power serve as intermediary elements that correct aberrations introduced by the large aperture, allowing bright imaging performance.
4Weight of moving object
If the weight of glass material is reduced, then the overall weight is reduced, but image formation performance deteriorates
Solution Approach 1:
The patent specifies precise parameters for glass materials including refractive indices (nd: 1.45-1.90, νd: 20-70) and partial dispersion ratios (θgF: 0.020-0.040). By optimizing these material parameters rather than simply reducing weight, the system achieves both lightweight construction and high image formation performance.
Solution Approach 2:
The optical system uses composite glass materials with carefully selected properties. Different glass types are combined in the lens groups to achieve weight reduction while maintaining or improving optical performance through the complementary characteristics of the various materials.
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 system achieves high imaging performance, reduced size and weight, and minimized focus breathing, while maintaining a large aperture ratio, through optimized lens group movements and material selection.
Implementation Method 1
a third lens group G3 having a positive refractive power, a fourth lens group G4 having a positive refractive power, and a fifth lens group G5 having a negative refractive power
Implementation Method 2
the imaging optical system includes an aperture diaphragm S between a lens surface in the second lens group G2 closest to the image side and a lens surface in the fourth lens group G4 closest to the object side
Data Source
AI summary
An imaging optical system includes, in order from an object side to an image side, a first lens group, a second lens group, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power, in which, when focusing from an infinite distance object to a close distance object, the first lens group remains stationary with respect to an image surface, the second lens group moves to the object side along an optical axis, the third lens group remains stationary with respect to the image surface, the fourth lens group moves to the object side along the optical axis, and the fifth lens group remains stationary with respect to the image surface, the imaging optical system includes an aperture diaphragm, and the imaging optical system satisfies a predetermined conditional expression.