Three-Element Aspheric Lens System for Reduced Tolerance Sensitivity
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Solution Overview
Problem
Traditional wide-angle photographic objective lens systems for small format digital image sensors are overly sensitive to manufacturing misalignment errors, leading to reduced image sharpness due to stringent centering requirements, which are difficult to consistently meet.
Innovation Solution
A compact three-lens system with aspheric surfaces made from polymeric plastics, where the first and third lenses are made from the same crown-like material and the second lens from a flint-like material, featuring a multilayer infrared cutoff filter, and an aperture stop shifted towards the object plane to minimize chief ray angles and desensitize the system to manufacturing tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a wide-angle photographic objective lens system is designed for small format digital image sensors, then the angular field of view increases, but the sensitivity to manufacturing misalignment errors increases
Solution Approach 1:
The lens system is divided into three separate lens elements (first, second, and third lenses) with distinct functions. The first lens has positive power, the second has negative power, and the third has positive power. This segmentation allows each element to be optimized for specific optical functions while reducing the overall sensitivity to misalignment compared to a single wide-angle lens element.
Solution Approach 2:
Each lens element is assigned different local optical properties through the use of aspheric surfaces and different plastic materials. The aspheric surfaces provide localized correction of optical aberrations in specific regions of each lens element, enabling the system to maintain wide-angle performance while reducing sensitivity to manufacturing tolerances through localized optimization.
2Volume of moving object
If the lens system is scaled down for small format sensors, then the size decreases, but the tolerance requirements become tighter
Solution Approach 1:
The invention changes the parameters of the lens system by using aspheric surfaces instead of spherical surfaces, and by selecting specific plastic materials with appropriate refractive indices. These parameter changes allow the scaled-down lens system to maintain adequate performance with relaxed tolerance requirements compared to traditional scaled-down spherical lens systems.
Solution Approach 2:
The lens system uses composite construction with three different plastic materials having different refractive indices and dispersion properties. This composite approach allows the system to achieve the desired optical performance in a compact form while being less sensitive to manufacturing tolerances, as the different materials compensate for each other's manufacturing variations.
3Illumination intensity
If traditional photographic objective designs are used, then the chief ray angles are similar to field angles, but the image sharpness is reduced due to manufacturing errors
Solution Approach 1:
The lens design dynamically controls the chief ray angles through the specific arrangement and powers of the three lens elements. The aperture stop is positioned between the first and second lenses, and the aspheric surfaces are configured to dynamically redirect chief rays to maintain smaller incident angles on the image plane across the wide field of view, thereby maintaining image sharpness consistency.
Solution Approach 2:
The second lens with negative power acts as an intermediary element between the first and third lenses. This intermediate negative lens helps to control and reduce the chief ray angles before they reach the image plane, serving as a mediator that corrects the excessive chief ray angles that would otherwise be present in a simple wide-angle lens design.
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 reduced sensitivity to manufacturing misalignment errors, ensuring consistent image sharpness and maintaining high image quality across a wide angular field of view while meeting size and resolution requirements for small format digital image sensors.
Implementation Method 1
At least one of the aspheric surfaces of the three lenses is also coated with a multilayer infrared cutoff filter to block infrared wavelengths from reaching the image sensors at the image focal plane.
Implementation Method 2
The lens system has three lenses, each of which has two aspheric surfaces. All three lenses are made from a plastic material.
Data Source
AI summary
The present invention is a compact lens system for use as a wide-field photographic objective with small format digital image sensors having a pixel dimension less than 0.010 mm. The f-number of the lens system is 2.9740, and the effective focal length of the system is 3.85 mm. The full angular field of view of the lens system is 61 degrees, and the chief ray incidence angles on the image plane are less than 18 degrees. The system comprises three plastic lenses, each having two aspheric surfaces. At least one of the aspheric surfaces in the system is coated with a multilayer infrared cut-off filter for blocking infrared wavelengths from the image sensors. The lens system has a reduced sensitivity to manufacturing tolerances, particularly lateral misalignment of optical elements and surfaces.