Four-element image pickup lens with negative biconcave second element
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Solution Overview
Problem
Existing image pickup lenses face challenges in achieving both size reduction and high optical performance, particularly when accommodating image pickup devices with a large number of pixels, as they struggle with chromatic aberration correction and manufacturing sensitivity due to strong refractive powers and biconvex lens elements that can lead to ghosting and image quality deterioration.
Innovation Solution
An image pickup lens configuration with four elements, including a first positive refractive power lens, a second negative refractive power biconcave lens, a third positive refractive power meniscus lens, and a fourth negative refractive power lens, where the second lens element's focal length and Abbe number are optimized to balance refractive power and correct aberrations, and the aperture stop is positioned near the image side to increase light incidence and reduce total optical length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If three lens elements are used to reduce total optical length, then size reduction is achieved, but chromatic aberration correction becomes insufficient
Solution Approach 1:
The lens system is divided into four distinct lens elements (first positive, second negative, third positive, fourth negative) arranged in sequence. This segmentation allows each element to contribute differently to the overall optical function, with the negative elements specifically addressing chromatic aberration while the positive elements provide focusing power, achieving both compact size and aberration correction.
Solution Approach 2:
The patent employs specific parameter relationships including conditional expressions for focal lengths (f1/f, f2/f, f3/f, f4/f) and Abbe numbers (νd1, νd2, νd3, νd4) of each lens element. These parameter constraints ensure that the four-element configuration achieves optimal chromatic aberration correction while maintaining a compact total optical length suitable for high-pixel image pickup devices.
2Manufacturing precision
If four lens elements are used to correct aberrations, then chromatic aberration is corrected well, but total optical length increases
Solution Approach 1:
Instead of using traditional configurations with strong positive refractive powers that increase optical length, the patent inverts the approach by employing negative refractive power elements (second and fourth lens elements) with specific focal length ratios. This inverted configuration achieves effective chromatic aberration correction while controlling the total optical length to remain compact.
Solution Approach 2:
The patent implements specific parameter relationships including the conditional expression 0.2 < |f2/f| < 0.5 for the second negative lens element and 0.3 < |f4/f| < 0.6 for the fourth negative lens element. These parameter constraints optimize the balance between aberration correction capability and total optical length, enabling compact design without sacrificing optical performance.
3Power
If strong refractive power is used in first and second lens elements, then focusing ability is improved, but manufacturing sensitivity increases
Solution Approach 1:
The patent distributes the refractive power across four lens elements with specific focal length ratios rather than concentrating strong refractive power in fewer elements. The conditional expressions constrain the focal lengths of each element relative to the total focal length f, ensuring that no single element requires excessively strong refractive power. This parameter optimization reduces manufacturing sensitivity while maintaining adequate focusing ability.
Solution Approach 2:
The refractive power is segmented across four elements with alternating positive and negative signs. The first element provides initial focusing with moderate positive power, the second element introduces negative power for chromatic correction, the third element adds positive power, and the fourth element provides final negative power adjustment. This segmentation of refractive power reduces the burden on any single element, lowering manufacturing sensitivity.
4Power
If biconvex third lens element is used, then positive refractive power is achieved, but ghosting occurs due to total reflection of marginal rays
Solution Approach 1:
The third lens element is designed with asymmetric curvature where the object-side surface has a different radius of curvature than the image-side surface. Specifically, the object-side surface has a smaller radius of curvature than the image-side surface, creating an asymmetric meniscus shape that redirects marginal rays to prevent total internal reflection and ghosting while maintaining the required positive refractive power.
Solution Approach 2:
The patent specifies parameter constraints for the third lens element including its focal length ratio 0.2 < f3/f < 0.4 and Abbe number νd3 satisfying specific relationships. These parameter changes, combined with the asymmetric meniscus shape, ensure that the element provides adequate positive refractive power while controlling ray angles to prevent ghosting phenomena.
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 aberrations, reduces manufacturing sensitivity, and achieves a compact size while maintaining high optical performance, preventing ghosting and ensuring good image quality for high-pixel image pickup devices.
Implementation Method 1
a first lens element having a positive refractive power, a second lens element having a negative refractive power
Data Source
AI summary
An image pickup lens includes, in order from an object side to an image side, an aperture stop, a first lens element having a positive refractive power, a second lens element having a negative refractive power and a biconcave shape, a third lens element having a positive refractive power and a meniscus shape whose concave surface faces the object side, and a fourth lens element having a negative refractive power. In the image pickup lens, the following conditional expressions are satisfied,0.20<f/|f2|<0.9νd1−νd2>25where f denotes the focal length of the entire lens system, f2 denotes the focal length of the second lens element, νd1 denotes the Abbe number of the first lens element, and νd2 denotes the Abbe number of the second lens element.