Meniscus Negative Lens Optical System for Wide-Angle Aberration Control

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Solution Overview

Problem

In image pickup optical systems with wide field angles, achieving high resolution while correcting aberrations such as field curvature and distortion is challenging due to asymmetric lens arrangements, leading to issues like ghosting and flare from light flux reflections.

Innovation Solution

An optical system with a front unit having negative refractive power, an aperture stop, and a rear unit with positive refractive power, including a meniscus-shaped negative lens closest to the object side, where specific conditional expressions for focal length and curvature radius ratios are satisfied to optimize lens structure and reduce aberrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the refractive power of the first lens unit is strengthened to achieve wide field angle, then the field angle is increased, but distortion aberration and field curvature are abundantly generated

Engineering Contradiction:

Improvefield angleVSAvoidaberration correction

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The first lens unit is divided into multiple lens elements (first lens, second lens, and optionally third lens) with different refractive powers and shapes. This segmentation allows each element to contribute differently to the overall optical function, enabling wide field angle while correcting aberrations through the combined effect of multiple elements rather than relying on a single strong negative lens.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs asymmetric arrangement of lens elements within the first lens unit, with each lens element having different shapes, refractive powers, and positions. The meniscus-shaped lenses with specific curvature relationships create an asymmetric optical path that corrects distortion and field curvature while maintaining wide field angle capability.

Inventive Principle:

Principle #4Asymmetry

2Adaptability or versatility

If the curvature radii of lens surfaces are reduced to achieve wide field angle, then the field angle is increased, but ghost and flare are generated due to light flux reflection

Engineering Contradiction:

Improvefield angleVSAvoidghost and flare

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potentially harmful reflected light flux into a beneficial effect by designing the lens surfaces with specific curvature relationships. The reflected light from the second lens is directed to fall on the first lens in a controlled manner, and through the specific curvature design (where R1/R2 is within 0.05 to 0.30), this reflected light is properly managed to avoid ghost and flare while maintaining wide field angle.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent optimizes the curvature radii parameters of the lens surfaces, specifically setting the ratio R1/R2 within a precise range (0.05 to 0.30) and controlling the focal length ratio fg1/fw within (0.3 to 0.6). These parameter changes ensure that light flux reflections are minimized or properly directed, preventing ghost and flare while achieving wide field angle.

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If asymmetric lens arrangement is used to achieve wide field angle, then the field angle is increased, but various aberrations such as field curvature and distortion are abundantly generated

Engineering Contradiction:

Improvefield angleVSAvoidaberration correction

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

Different lens elements within the first lens unit are assigned different local qualities - specific shapes (meniscus, biconvex), different refractive powers, and different positions. Each lens element is optimized for its local function, with the first lens having specific curvature characteristics and the second lens having complementary characteristics, allowing the asymmetric arrangement to achieve wide field angle while correcting aberrations through the coordinated local properties of each element.

Inventive Principle:

Principle #3Local quality

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 effectively achieves a wide field angle with high optical characteristics, reducing ghosting and flare, and maintaining satisfactory image quality across the entire screen.

Implementation Method 1

a front unit (LF) having a negative refractive power; an aperture stop; and a rear unit (LR) having a positive refractive power, in which the front unit includes a meniscus-shaped negative lens (g1) closest to the object side

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS9684155B2Optical system and image pickup apparatus including the same

Publication Date: 2017.06.20 CANON KK

AI summary

In an optical system including, in order from an object side to an image side: a front unit (LF) having a negative refractive power; an aperture stop; and a rear unit (LR) having a positive refractive power, the front unit (LF) includes a meniscus-shaped negative lens (g1) closest to the object side, and a focal length (fw) of the entire optical system, a focal length (fg1) of the meniscus-shaped negative lens (g1), and a curvature radius (R2) of a lens surface on the image side of the meniscus-shaped negative lens (g1) are appropriately set.