Optical System with Negative and Positive Lens Units for Wide Wavelength Imaging
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Solution Overview
Problem
Imaging optical systems for monitoring cameras face challenges in achieving a wide angle of view and excellent optical performance over a wide wavelength range from visible to near-infrared, particularly in low-light conditions, due to issues with chromatic aberration and insufficient near-infrared light availability.
Innovation Solution
The optical system comprises a first lens unit with negative refractive power, an aperture stop, and a second lens unit with positive refractive power, where specific conditional expressions are satisfied to correct chromatic aberrations and ensure a large aperture ratio and wide angle of view, including the use of cemented lenses and optical blocks for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the optical system uses conventional lens configurations to achieve wide angle of view and wide wavelength range coverage, then the angle of view and wavelength range are improved, but chromatic aberration and secondary spectrum increase
Solution Approach 1:
The patent employs multiple lens materials with different dispersion characteristics (negative lens material and positive lens material) to construct composite lens units. The negative lens unit with specific partial dispersion ratio θIR(G1n) and the positive lens unit with partial dispersion ratio θIR(G2p) work together to correct chromatic aberration across the wide wavelength range from visible to near-infrared, resolving the contradiction between wide wavelength coverage and chromatic aberration control
Solution Approach 2:
The patent applies different optical properties to different parts of the system: the negative lens unit has specific dispersion characteristics (θIR(G1n) < 0.82) while the positive lens unit has complementary characteristics (θIR(G2p) > 0.78). This local differentiation of optical properties enables targeted correction of chromatic aberration in different wavelength regions, achieving both wide wavelength coverage and high imaging precision
2Illumination intensity
If the optical system increases aperture ratio for low-light performance, then the light gathering capability is improved, but optical performance and aberration control deteriorate
Solution Approach 1:
The patent optimizes specific parameter ranges: the negative lens unit has focal length ratio -0.5 < f1/f < 0, the positive lens unit has 0 < f2/f < 0.5, and the ratio of their focal lengths satisfies -2.0 < f1/f2 < -0.5. These parameter optimizations enable the system to maintain f/1.0 large aperture while correcting spherical aberration, coma, and chromatic aberration, achieving both high light gathering capability and excellent optical performance
Solution Approach 2:
The patent employs a focus adjustment mechanism that moves the negative lens unit and positive lens unit relative to each other along the optical axis. This dynamic adjustment capability allows the system to maintain optimal aberration correction across different focus distances while preserving the large aperture ratio, resolving the contradiction between aperture size and optical performance
3Manufacturing precision
If the optical system uses multiple lens units for aberration correction, then the imaging performance is improved, but the device complexity increases
Solution Approach 1:
The patent divides the optical system into two functional segments: a negative lens unit (G1) and a positive lens unit (G2), separated by an aperture stop. This segmentation allows independent optimization of each unit's dispersion characteristics (θIR(G1n) and θIR(G2p)) to correct different aspects of chromatic aberration, achieving comprehensive aberration correction with minimal lens units and reduced overall complexity
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 achieves excellent imaging performance across the visible to near-infrared range, with reduced secondary spectrum and increased backfocus, enabling effective imaging even in low-light conditions.
Implementation Method 1
a first lens unit with a negative refractive power, an aperture stop, and a second lens unit with a positive refractive power
Data Source
AI summary
Provided is an optical system including, in order from an object side to an image side, a first lens unit having a negative refractive power, an aperture stop, and a second lens unit having a positive refractive power, in which an average value θIR(G2p)AVE of partial dispersion ratios of materials of positive lenses included in the second lens unit and an average value θIR(G2n)AVE of partial dispersion ratios of materials of negative lenses included in the second lens unit are appropriately set, provided that BF and F are a backfocus and a focal length of the optical system at a wavelength of 1050 nm, respectively, and a partial dispersion ratio of a material is θ=(Ns−Nm)/(Ns−Nl), where Ns, Nm, and Nl are refractive indices of the material at wavelengths of 400 nm, 1050 nm, and 1700 nm, respectively.