Optical System Diffractive Element Chromatic Aberration Correction
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Solution Overview
Problem
Conventional optical systems using diffractive optical elements require further improvement in optical performance, particularly in correcting chromatic aberrations and reducing system size while maintaining weight reduction and minimizing stray light.
Innovation Solution
The optical system incorporates a focusing group that moves upon focusing, featuring a diffractive optical element and negative lens elements disposed to satisfy specific refractive index and Abbe number conditions, along with a vibration-isolating group to correct axial and lateral chromatic aberrations, spherical aberrations, and curvature of field, while optimizing the focal length and total length ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a diffractive optical element is used to downsize the optical system, then the system size is reduced, but chromatic aberrations worsen
Solution Approach 1:
A negative lens element with specific refractive index (1.910 < nd1n + 0.006×νd1n) and Abbe number (35 < νd1n) is introduced as an intermediary component between the diffractive optical element and the focusing group. This negative lens acts as a mediator that corrects the chromatic aberrations generated by the diffractive optical element, allowing the system to maintain both compact size and optical quality
Solution Approach 2:
The patent employs a composite optical system combining diffractive optical elements with specific negative lens materials having controlled refractive indices and dispersion properties. By compositeing materials with different optical characteristics (positive and negative lens elements with specific nd and νd values), the system achieves both size reduction and chromatic aberration correction
2Object-affected harmful factors
If lens elements are added to correct chromatic aberrations, then optical performance is improved, but system weight increases
Solution Approach 1:
The patent optimizes the optical parameters of existing lens elements by precisely controlling the refractive index (nd) and Abbe number (νd) within specific ranges. By changing these material parameters rather than simply adding more elements, the system corrects chromatic aberrations while minimizing weight increase. The negative lens element's specific parameter range (1.910 < nd1n + 0.006×νd1n, 35 < νd1n) enables efficient aberration correction with minimal mass
Solution Approach 2:
Instead of uniformly increasing system mass, the patent applies local quality optimization by selecting specific lens elements with tailored refractive indices and dispersion properties at critical positions. The negative lens element with specific nd and νd values is strategically placed to correct chromatic aberrations locally without requiring comprehensive reinforcement of the entire system structure
3Object-affected harmful factors
If the focal length ratio f/fpf is reduced to improve aberration correction, then chromatic aberration correction is enhanced, but the system becomes more complex
Solution Approach 1:
The patent establishes specific parameter ranges for the focal length ratio (0.030 < f/fpf < 0.050) and total length ratio (0.55 < TL/f < 0.65) to optimize aberration correction. By defining precise parameter boundaries rather than using complex multi-element designs, the system achieves effective chromatic aberration correction with controlled complexity
Solution Approach 2:
The patent applies partial action by focusing correction efforts on the most critical chromatic aberrations through the negative lens element with specific optical parameters, rather than attempting to correct all possible aberrations with a complex multi-element design. This targeted approach achieves sufficient optical performance with simpler system architecture
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 effectively corrects axial and lateral chromatic aberrations, reduces system size, and minimizes stray light, achieving improved optical performance and weight reduction.
Implementation Method 1
an optical system which is downsized using diffractive optical elements
Implementation Method 2
a negative lens element disposed on the object side of the diffractive optical element... satisfy the following expressions (1-2) and (1-3): nd1n+0.006×νd1n1.910, 35d1n
Data Source
AI summary
An optical system (OL) used for an optical apparatus such as a camera (1) includes a focusing group (Gf) that moves upon focusing, a diffractive optical element (GD) disposed on an object side of the focusing group (Gf) and a negative lens element (L1n) disposed on the object side of the diffractive optical element (GD). The optical system (OL) satisfies the following expressions0.030<f/fpf<0.050nd1n+0.006×νd1n<1.91035<νd1n where,f: focal length of whole system in infinity focusing statefpf: focal length of diffractive optical element (GD)nd1n: refractive index of medium of negative lens element (L1n) on d-lineνd1n: Abbe number of medium of negative lens element (L1n) on d-line.