Multifocal Image Pickup Lens for Uniform Focal Depth
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Solution Overview
Problem
Image pickup devices with bifocal lens systems have a large focal depth that varies between the center and the outer part of the image plane, leading to deterioration in resolution.
Innovation Solution
An image pickup lens with a multifocal surface and a diffractive optical element, where the distance between the multifocal surface and the aperture stop is optimized to maintain focal depth and reduce aberrations, ensuring uniform resolution across the image plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a bifocal lens system is used to achieve large focal depth, then the focal depth is increased, but the resolution deteriorates due to focal depth variation between center and outer parts
Solution Approach 1:
The lens surface is divided into multiple regions (first region, second region, third region) with different curvatures. The first region has a first curvature, the second region has a second curvature, and the third region has a third curvature. This local differentiation allows each region to contribute to different aspects of focal depth control, enabling uniform focal depth across the entire image plane while maintaining high resolution.
Solution Approach 2:
The lens surface is segmented into distinct functional zones: a central first region, a peripheral second region, and an intermediate third region. Each segment is optimized for specific optical performance, with the first region providing primary focusing, the second region extending focal depth at peripheral locations, and the third region transitioning between the two.
2Stability of the object's composition
If the focal depth is increased from center to outer part of image plane, then the uniformity of focal depth is improved, but the resolution may decline
Solution Approach 1:
The curvature parameter of the lens surface is changed across different regions. The first region has a first curvature value, the second region has a second curvature value, and the third region has a third curvature value. By carefully selecting and varying these curvature parameters, the lens achieves uniform focal depth extension from center to outer parts while maintaining the resolution necessary for high-quality imaging.
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 solution provides a compact image pickup device with high-resolution performance and a large focal depth from the center to the outer part of the image plane, suppressing resolution decline and minimizing flare, especially in high-brightness conditions.
Implementation Method 1
on at least one lens surface of the at least one lens, a multifocal lens surface having a plurality of surface areas having different focal points
Implementation Method 2
An aperture stop is placed adjacent to the multifocal lens surface
Implementation Method 3
An image pickup lens with a multifocal surface and a diffractive optical element
Data Source
AI summary
The present invention provides an image pickup lens with a large focal depth from the center to the outer part of an image plane formed on an image sensor and capable of maintaining its focal depth within a practical range and thus suppressing a decline in the resolution. An image pickup lens 7 includes, in order from the object side to the image plane side, an aperture stop 5, a first lens 1 that is a biconvex lens having positive power, a second lens 2 that is a meniscus lens having negative power and whose lens surface facing the object side is convex, a third lens 3 that is a meniscus lens having positive power and whose lens surface facing the object side is concave, and a fourth lens 4 that is a biconcave lens having negative power. The image pickup lens 7 includes a multifocal lens on the lens surface of the first lens 1 facing the object side. D and Ymax satisfy the following conditional expression (1):0≦D/Ymax≦0.1 (1)where D is an absolute value of the distance between the multifocal lens surface and a surface of the aperture stop on the optical axis, and Ymax is the absolute value of the maximum image height on an image plane formed on the image sensor.