Four-Element Image Pickup Lens with Negative Fourth Lens
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional image pickup lenses face challenges in downsizing while maintaining efficient aberration correction, particularly with four-element lenses, which often result in longer back focus and insufficient peripheral image area performance due to limited negative refractive power and inadequate aberration correction.
Innovation Solution
A four-element image pickup lens design featuring an aperture stop, a first positive refractive power lens, a second negative refractive power lens, a third positive refractive power lens, and a fourth negative refractive power lens with a concave surface facing the object side, including at least one aspheric surface, optimized by specific conditional expressions to achieve reduced total length and improved aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a four-element image pickup lens with positive fourth lens (inverted Ernostar type) is used, then aberration correction is improved, but back focus becomes longer and device size increases
Solution Approach 1:
The patent inverts the conventional Ernostar type lens configuration by making the fourth lens have negative refractive power instead of positive refractive power. This inversion allows the principal point to be positioned closer to the object side, thereby shortening the back focus distance while maintaining the aberration correction benefits of a four-element lens structure.
2Device complexity
If only one lens has negative refractive power in a four-element lens, then device complexity is reduced, but Petzval's sum correction becomes difficult and peripheral image performance deteriorates
Solution Approach 1:
The patent applies local quality by making both the second and fourth lenses have negative refractive power, creating a specific distribution of refractive powers throughout the lens system. This localized configuration of negative refractive power in specific lens elements enables effective correction of Petzval's sum and improvement of peripheral image performance while maintaining overall system simplicity.
3Length of stationary object
If total length of image pickup lens is shortened, then device size is reduced, but imaging field angle becomes narrower and aberration correction becomes insufficient
Solution Approach 1:
The patent utilizes parameter changes by optimizing the refractive indices and curvatures of the lens elements, particularly making the fourth lens with negative refractive power and aspheric surface. This parameter optimization allows the lens to achieve a narrow imaging field angle while maintaining adequate aberration correction and compact total length, balancing miniaturization requirements with optical performance.
4Device complexity
If fourth lens has weak negative refractive power in telephoto type, then device complexity is reduced, but back focus remains long and downsizing is insufficient
Solution Approach 1:
The patent applies parameter changes by making the fourth lens have strong negative refractive power and an aspheric surface, rather than weak negative refractive power. This parameter adjustment significantly shortens the back focus distance and enables effective downsizing of the image pickup lens while maintaining manageable device complexity through the telephoto type configuration.
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 design achieves a smaller lens size with enhanced aberration correction across the image area, allowing for a more compact and efficient image pickup apparatus suitable for mobile terminals with solid image pickup elements.
Implementation Method 1
a fourth lens having a negative refractive power whose surface facing the object side is a concave surface
Implementation Method 2
The fourth lens includes at least one optical surface in an aspheric shape
Implementation Method 3
an image pickup lens which forms an inverted real image of an object on a photo-electric converter
Data Source
AI summary
The present invention provides an image pickup lens for forming a light flux from a subject into an image on a photo-electric converter of a solid image pickup element, and the image pickup lens includes, in order from an object side thereof: and aperture stop; a first lens having a positive refractive power; a second lens having a negative refractive power; a third lens having a positive refractive power; and a fourth lens having a negative refractive power. The fourth lens includes a concave surface facing the object side and at least one optical surface has an aspheric shape in the fourth lens. The image pickup lens satisfies the predetermined condition according to a curvature radius of the surfaces of the fourth lens and a focal length.