Radial Transmittance Optical Element for Defocus Image Quality

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Solution Overview

Problem

Conventional imaging optical systems using apodization filters can obtain good defocus images but often result in a reduction of the light amount of the on-axis light flux, leading to a decrease in image quality.

Innovation Solution

An imaging optical system with a transmittance distribution that changes radially, minimizing transmittance at specific positions away from the optical axis, while maintaining or increasing transmittance at the optical axis, to balance defocus image quality and on-axis light flux, utilizing a transmittance distribution element with a centrosymmetric design and absorptive or reflective materials.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If an apodization filter with transmittance decreasing radially is used, then defocus image quality is improved, but on-axis light flux amount is reduced

Engineering Contradiction:

Improvedefocus image qualityVSAvoidon-axis light flux amount

Core Design Contradiction:

Measurement precisionVSIllumination intensity

Solution Approach 1:

The optical element applies different transmittance characteristics to different regions: the central region (within radius rd) maintains high transmittance to preserve on-axis light flux, while the peripheral region (beyond radius rd) has reduced transmittance to improve defocus image quality. This spatially varying transmittance distribution resolves the contradiction by optimizing each region's function locally.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the transmittance parameter as a function of radial position from the optical axis. By defining transmittance as a variable parameter that decreases only beyond a certain radius rd, the system achieves both high central transmittance for focus light and reduced peripheral transmittance for defocus quality, transforming the uniform transmittance parameter into a spatially dependent parameter.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If transmittance is reduced radially to obtain defocus image, then defocus clarity is improved, but overall light quantity is lowered

Engineering Contradiction:

Improvedefocus clarityVSAvoidlight quantity

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of reducing transmittance across the entire optical element, the invention applies transmittance reduction only partially - specifically in the peripheral region beyond radius rd. This partial action is sufficient to improve defocus clarity while avoiding excessive transmittance reduction that would unnecessarily lower overall light quantity.

Inventive Principle:

Principle #16Partial or excessive action

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

Successfully acquires defocus images with improved clarity while suppressing the decrease in on-axis light flux, maintaining image quality and preventing excessive reduction in transmittance.

Implementation Method 1

an optical element having a transmittance that changes in a radial direction perpendicular to an optical axis. The transmittance of the optical element is minimized at a first position in the radial direction separated from an optical axis position of the optical element by a distance smaller than an effective radius rd of the optical element

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentUS11221459B2Imaging optical system and imaging apparatus

Publication Date: 2022.01.11 CANON KK

AI summary

An imaging optical system includes at least one lens, and an optical element having a transmittance that changes in a radial direction perpendicular to an optical axis. The transmittance of the optical element is minimized at a first position in the radial direction separated from an optical axis position of the optical element by a distance smaller than an effective radius rd of the optical element. The transmittance at the first position is smaller than that at the optical axis position and that at a second position separated from the optical axis position by rd.