Telephoto Lens Design with Diffractive Element for Chromatic Aberration Correction
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Solution Overview
Problem
Telephoto lenses with long focal lengths face increased axial chromatic aberration and chromatic aberration of magnification, making it difficult to achieve both proper correction and a short overall lens length, especially when using refractive optical systems or diffractive optical elements.
Innovation Solution
A telephoto-type photographing optical system is designed with a positive lens and a diffractive optical element closer to the object side than the light axis intersection P, and a negative lens closer to the image side than P, both formed from materials with specific Abbe number and partial dispersion ratio conditions, ensuring proper correction of chromatic aberrations while maintaining a short overall lens length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the focal length is increased to achieve a telephoto lens, then the magnification and reach are improved, but axial chromatic aberration and chromatic aberration of magnification are increased
Solution Approach 1:
The patent combines multiple lens materials with different dispersion characteristics (low-dispersion material for the positive lens and high-dispersion material for the negative lens) to correct chromatic aberrations while maintaining long focal length telephoto capability
Solution Approach 2:
A diffractive optical element is introduced as an intermediary component to correct chromatic aberrations by utilizing diffraction effects that complement the refractive properties of the lens materials
2Length of moving object
If the positive refractive power of the front lens unit and negative refractive power of the rear lens unit are increased to reduce overall lens length, then the lens becomes more compact, but a large amount of chromatic aberration occurs
Solution Approach 1:
The patent uses composite lens structures combining materials with contrasting dispersion properties (low-dispersion positive lens and high-dispersion negative lens) to correct chromatic aberrations even when high refractive powers are used for lens compactness
Solution Approach 2:
The diffractive optical element serves as a mediator to correct chromatic aberrations introduced by the high refractive power design, enabling short overall lens length without sacrificing optical quality
3Length of moving object
If a diffractive optical element is used to correct chromatic aberrations and reduce overall lens length, then optical performance is improved, but when the overall lens length is made excessively short, chromatic aberrations may not be properly corrected
Solution Approach 1:
The patent optimizes specific parameter ranges including the focal lengths of individual lens units, the position of the diffractive optical element, and the dispersion characteristics of lens materials to achieve proper chromatic aberration correction at reduced overall lens length
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 effectively corrects both axial chromatic aberration and chromatic aberration of magnification, achieving high optical performance with a reduced overall lens length, suitable for image pickup apparatuses like digital cameras.
Implementation Method 1
a method using a diffractive optical element is known
Implementation Method 2
The positive lens is formed using a low-dispersion material having extraordinary dispersion. The negative lens is formed using a high-dispersion material.
Data Source
AI summary
A photographing optical system includes at least one of a positive lens and diffractive optical element being provided closer to an object side of the system than an intersection P of a light axis and paraxial chief ray, and a negative lens, provided closer to an image side than the intersection. The positive lens and the negative lens are formed of materials satisfying the following conditions when the maximum height of a paraxial marginal ray, passing through a lens surface, from the light axis at a location closer to the object side than the intersection is greater than a maximum height of the paraxial marginal ray, passing through a lens surface, from the light axis at a location closer to the image than the intersection:−0.0015 ×νd +0.6425 <θgF60 <νd where νd is an Abbe number and θgF is a partial dispersion ratio.