Correction Lens Unit for Atmospheric Pressure Focal Shift

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Solution Overview

Problem

Changes in atmospheric pressure cause significant focal position shifts in zoom lenses, particularly those with high refractive power, leading to reduced image capturing quality, especially in environments different from normal pressure conditions.

Innovation Solution

A lens apparatus with zoom lens units and a correction lens unit that moves along the optical axis to compensate for focal position changes, adhering to the inequality 0.4 < |fv/fw| < 9, where fv is the focal length of the smallest absolute value zoom lens unit and fw is the focal length at the wide-angle end, to minimize focal position shifts due to atmospheric pressure changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a zoom lens with high refractive power is used to achieve compact size and high magnification variation, then the lens can be more compact and versatile, but the focal position shift due to atmospheric pressure changes increases significantly

Engineering Contradiction:

Improvemagnification variationVSAvoidfocal position stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The lens system is divided into multiple lens units with different functions: variable magnification lens units for zooming and a correction lens unit specifically for compensating atmospheric pressure effects. This segmentation allows each unit to be optimized for its specific purpose while working together to achieve both compactness and stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The correction lens unit acts as an intermediary element that specifically addresses the harmful effect of atmospheric pressure changes on the focal position. By introducing this dedicated correction mechanism, the system can maintain focal stability despite using high refractive power lens units for compactness.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If atmospheric pressure changes are compensated by moving the stage holding the substrate, then focal position stability is improved, but the system complexity and cost increase

Engineering Contradiction:

Improvefocal position stabilityVSAvoidsystem complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The atmospheric pressure compensation function is extracted from the substrate stage and transferred to a dedicated correction lens unit within the optical system. This allows the stage to remain simple while the optical system handles the compensation, reducing overall system complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The mechanical compensation approach (moving the substrate stage) is replaced with an optical compensation approach (moving the correction lens unit). This substitution reduces mechanical complexity in the stage system while achieving the same focal position stability goal.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If a smaller pixel pitch is used to achieve higher pixel resolution, then image quality improves, but the depth of focus becomes shallower making focal position shifts more noticeable

Engineering Contradiction:

Improvepixel resolutionVSAvoidfocal position tolerance

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The correction lens unit performs preliminary compensation for atmospheric pressure-induced focal position shifts before the light reaches the image sensor. This preemptive correction ensures that even with shallow depth of focus from small pixel pitch, the focal position remains accurate under varying atmospheric conditions.

Inventive Principle:

Principle #9Preliminary anti-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

Effectively reduces focal position shifts under varying atmospheric pressures, maintaining image quality and stability across different environments by accurately correcting focal position changes through the use of a correction lens unit and atmospheric pressure measurement.

Implementation Method 1

a change in a focal position of a projecting optical system caused by change in an atmospheric pressure

Methodology Applied

Scientific EffectAtmospheric pressure change effect on focal position:

Data Source

PatentUS11573410B2Lens apparatus, image pickup apparatus, method of correcting change in focal position, and storage medium

Publication Date: 2023.02.07 CANON KK

AI summary

A lens apparatus includes zoom lens units configured to move in an optical axis direction for zooming, and a correction lens unit configured to move in the optical axis direction to correct change in a focal position due to change in an atmospheric pressure. The lens apparatus satisfies an inequality 0.4<|fair_t/fw|<6 where fair_t is a composite focal length of an air lens included in one of the zoom lens units having a smallest absolute value of the composite focal length among the zoom lens units and fw is a focal length of the lens apparatus at a wide-angle end.