Wide-Angle Lens Anti-Reflection Layer Ghost Suppression
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Solution Overview
Problem
Wide-angle lenses experience a ring-shaped red ghost due to inadequate anti-reflection effects on the peripheral portion of the first lens's image-side surface, caused by a thin anti-reflection layer that fails to effectively manage light reflection in the long wavelength range.
Innovation Solution
A wide-angle lens design incorporating a negative meniscus first lens with a concave image-side surface, a negative second lens with a concave image-side surface, and an anti-reflection layer with a reflectance of 1.5% or less in the 430 nm to 850 nm wavelength range, ensuring effective light management across a wide wavelength spectrum, including near-infrared ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the anti-reflection layer is provided on the lens surface of the first lens on the image side with a large sag amount, then the field angle is widened, but the thickness of the anti-reflection layer becomes smaller than appropriate in the peripheral portion, causing inadequate anti-reflection effect for long wavelength light
Solution Approach 1:
The patent changes the optical parameters by introducing a negative meniscus second lens with specific curvature relationships. The key parameter change is setting the curvature radius of the image-side surface of the second lens (r22) to be smaller in absolute value than that of the object-side surface (r21), creating a strong negative lens effect that compensates for the reduced anti-reflection layer thickness while maintaining wide field angle performance
Solution Approach 2:
The patent uses a composite lens system combining a first negative meniscus lens and a second negative meniscus lens with specific material properties. The second lens has a refractive index nd2 between 1.40 and 1.70 and an Abbe number νd2 between 20 and 60, creating a composite optical system that achieves both wide field angle and effective anti-reflection through the synergistic effect of multiple lens elements with different optical characteristics
2Ease of manufacture
If the anti-reflection layer thickness is reduced in the peripheral portion to accommodate large sag amount, then manufacturing becomes easier, but ring-shaped red ghost occurs due to insufficient anti-reflection effect
Solution Approach 1:
The patent converts the potential harm of reduced anti-reflection layer thickness into a benefit by introducing a second negative meniscus lens that optically compensates for the thickness reduction. The strong negative power of the second lens (achieved by making |r22| < |r21|) counteracts the increased reflection from the thinner anti-reflection layer, transforming the manufacturing advantage into an effective optical solution that eliminates the red ghost while maintaining ease of manufacture
3Area of stationary object
If a negative meniscus first lens with large sag amount is used, then the field angle is widened, but the angle between the tangent to the peripheral portion and the optical axis becomes small
Solution Approach 1:
The patent applies an inverted approach by introducing a second negative meniscus lens that works in opposition to the first lens's large sag amount. Instead of reducing the first lens's sag, the second lens provides a counteracting optical effect with its own negative power, allowing the first lens to maintain its large sag for wide field angle while the second lens corrects the resulting small peripheral angle issue
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 effectively suppresses ring-shaped red ghosts by ensuring appropriate anti-reflection across the visible and near-infrared spectrum, while maintaining sufficient negative power and correcting various aberrations, thus enhancing image quality and reducing manufacturing costs.
Implementation Method 1
an anti-reflection layer having a reflectance of 1.5% or less in a wavelength range from 430 nm to 850 nm is provided on at least the lens surface of the first lens on the image side
Data Source
AI summary
A wide-angle lens includes a front group, an aperture, a rear group, and an infrared cut filter. The front group includes a first lens and a second lens arranged in order from a side closest to an object to an image side. In the wide-angle lens, an anti-reflection layer having a reflectance of 1.5% or less in a wavelength range from nm to 850 nm is provided on a lens surface of the first lens on the image side to suppress an occurrence of a ghost caused by light passing through a peripheral portion of the lens surface. Therefore, even if a film forming the anti-reflection layer is thinner than an appropriate value at the peripheral portion of the lens surface, the anti-reflection layer appropriately prevents reflection of light in a long wavelength range.