Scanner Lens Aberration Correction via Cemented Groups
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Solution Overview
Problem
Current scanner lenses with a small number of lenses struggle to correct axial color aberration, field curvature, and various aberrations over a wide angle of view, while maintaining high aperture efficiency and contrast in high spatial frequency ranges, which hinders downsizing and cost reduction.
Innovation Solution
A scanner lens configuration comprising a series of lens groups with specific refractive powers and an aperture stop, including cemented lenses and aspheric surfaces, satisfying conditions for back focus, focal length ratios, and air space to correct aberrations and achieve high contrast and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a small number of lenses are used to downsize and reduce manufacturing costs, then manufacturing cost and device complexity are reduced, but the ability to correct axial color aberration, field curvature, and various aberrations deteriorates
Solution Approach 1:
The lens is divided into five distinct lens groups (G1-G5) with specific refractive powers, where each group contains one or more lenses with carefully controlled parameters. This segmentation allows complex aberration correction functions to be distributed across multiple specialized components rather than requiring a single complex lens, thereby achieving high correction precision with a relatively small total number of lenses.
Solution Approach 2:
The patent employs composite lens structures including cemented lenses (e.g., L1 and L2 cemented together in G1) and combines different material types (plastic and glass) with specific refractive indices and Abbe numbers. This use of composite materials and structures enables effective correction of axial color aberration across a wide spectral range while maintaining a compact lens configuration.
2Length of moving object
If a wide angle of view of 30 degrees or more is achieved, then downsizing is enabled, but field curvature and various aberrations become more difficult to correct
Solution Approach 1:
The patent incorporates aspheric surfaces on multiple lens elements (including L1, L2, L4, L5, and L6) with specifically designed aspheric coefficients. These aspheric surfaces dynamically adjust the optical path to correct field curvature and off-axis aberrations across the wide 30-degree half-angle field of view, enabling compact conjugation length while maintaining high imaging precision across the entire field.
Solution Approach 2:
Different regions of the lens system are assigned different functional characteristics: the first lens group G1 with positive refractive power handles central field illumination, while subsequent groups with negative and positive powers progressively correct off-axis aberrations. The aspheric surfaces are strategically positioned to address specific local aberration patterns in different field regions, achieving uniform high-quality imaging across the wide angle.
3Loss of energy
If high aperture efficiency of about 100% in the periphery of angle of view is achieved, then light utilization is maximized, but lens complexity and manufacturing difficulty increase
Solution Approach 1:
The patent applies aspheric surface correction and specific refractive power distributions that provide slightly excessive correction capability for off-axis rays, ensuring that even peripheral rays at wide angles maintain optimal focus and achieve near-100% aperture efficiency. This partial over-correction approach compensates for inherent optical losses without requiring additional complex lens elements.
4Measurement precision
If high contrast in high spatial frequency range is achieved, then image quality is improved, but lens precision requirements and manufacturing difficulty increase
Solution Approach 1:
The patent uses plastic lens materials for several elements that can be manufactured with high precision aspheric surfaces through injection molding, effectively copying the ideal aspheric profiles with high fidelity. This manufacturing approach achieves the necessary surface precision for high spatial frequency contrast without the extreme difficulty of grinding and polishing glass aspheres, thereby maintaining high image quality while improving ease of manufacture.
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 configuration effectively corrects axial color aberration and field curvature over a wide angle, maintains high aperture efficiency, and reduces manufacturing costs by using fewer lenses and plastic materials, while enabling downsizing and high contrast in high spatial frequency ranges.
Implementation Method 1
a first lens group having a positive refractive power, comprising a first positive lens and a second negative lens which are cemented, a second lens group comprising a third negative lens, a third lens group comprising a fourth positive lens, a fourth lens group comprising a fifth negative lens, a fifth lens group comprising a sixth negative lens
Data Source
AI summary
A scanner lens includes a first lens group with a positive refractive power, having a first positive lens and a second negative lens which are cemented, second to fifth lens groups having a third negative lens, a fourth positive lens, a fifth negative lens, and a sixth negative lens, respectively, arranged in order from an object side to an image side, and an aperture stop disposed between the first and second lens groups. The scanner lens satisfies the following three conditions: 0.01<BF/L<0.10 0.50<f1/f<9.5 0.20<d10/f<0.90 where BF is a back focus of the scanner lens, L is a total lens length, f1 is a focal length of e-line of the first lens group, f is a focal length of e-line of the entire lens system and d10 is an air space between the fifth and six lenses.