Imaging Optical System with Negative First Lens Group
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Solution Overview
Problem
Existing imaging optical systems face challenges in achieving a wide angle-of-view with enlarged central image areas while maintaining a short overall length and large aperture, and effectively correcting various aberrations.
Innovation Solution
The proposed imaging optical system consists of a positive or negative first lens group, an aperture diaphragm, and a positive second lens group, with specific conditions for lens element configurations, including aspherical surfaces and Abbe numbers, to optimize focal lengths, radii of curvature, and refractive powers, allowing for a wide angle-of-view, enlarged central image, and aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the overall length of the imaging optical system is shortened, then the compactness is improved, but the aperture ratio becomes small
Solution Approach 1:
The imaging optical system is divided into multiple lens groups (first lens group with negative refractive power, second lens group with positive refractive power, and third lens group with positive refractive power). This segmentation allows each group to be optimized independently for specific functions, enabling the overall system to achieve both short length and large aperture by distributing optical power across groups rather than concentrating it in a single element.
Solution Approach 2:
Different lens elements within the system have different local optical properties. Specifically, the first lens group has negative refractive power to diverge light and reduce overall length, while the second and third lens groups have positive refractive power to converge light and maintain aperture. This local differentiation of optical properties allows the system to simultaneously achieve compactness and large aperture.
2Illumination intensity
If a large aperture is provided, then the light gathering ability is improved, but the overall length becomes long
Solution Approach 1:
Instead of using a conventional configuration where positive lens elements dominate and increase overall length to achieve large aperture, this invention inverts the approach by placing a lens group with negative refractive power at the object side. This negative lens group diverges light rays, allowing the subsequent positive lens groups to converge them more efficiently, thereby achieving large aperture with reduced overall length.
Solution Approach 2:
The invention changes the refractive power parameter of the first lens group to be negative, while the second and third lens groups have positive refractive power. This parameter configuration (negative-positive-positive) is optimized to achieve both large aperture and short overall length by balancing light divergence and convergence across the lens groups.
3Device complexity
If the first lens group has positive refractive power, then the image formation is simplified, but the angle-of-view becomes narrow and central image enlargement is reduced
Solution Approach 1:
The first lens group is designed with negative refractive power to create local optical effects that diverge light rays from the object side. This local negative power configuration expands the angle-of-view and enables central image enlargement, while the subsequent positive lens groups (second and third) compensate for the divergence and complete the image formation process.
Solution Approach 2:
The refractive power parameter of the first lens group is changed to negative values, which fundamentally alters the light path configuration. This parameter change enables the system to achieve wide angle-of-view and central image enlargement, while the positive refractive power of the second and third lens groups ensures proper image formation on the image plane.
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 enables a compact imaging optical system with a large aperture and effective aberration correction, achieving a wide angle-of-view and enlarged central image area while maintaining a short overall length.
Implementation Method 1
The negative lens element that is closest to the object side includes an aspherical surface on the object side thereof, the aspherical surface including a paraxial convex surface convexing toward the object side
Implementation Method 2
V designates the Abbe number with respect to the d-line of a lens element, within the second lens group, that is provided closest to the aperture diaphragm
Data Source
Figure 1~2D
Figure 3~4D
Figure 5~6D
AI summary
An imaging optical system includes a positive or negative first lens group including a negative lens element closest to the object, a diaphragm, and a positive second lens group. The negative lens element closest to the object has an object-side aspherical surface including a paraxial convex surface, a paraxial curvature that is the greatest within the effective aperture, and a portion within the effective aperture having a curvature less than 1/2 of the paraxial curvature. These conditions are satisfied: R1/f<1.35 D1/f>0.4 −2.5<f1/f<−1.3 V>56 "f" designates the overall focal length; f1, R1 and D1 respectively designate the focal length, paraxial radius of curvature of an object-side surface, and thickness, of the negative lens element closest to the object; and V designates the Abbe number regarding the d-line of a lens element, within the second lens group, closest to the diaphragm.