Movable ND Filter Exposure Control for Zoom Lens

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Solution Overview

Problem

Conventional image capturing apparatuses with zoom functions face challenges in maintaining exposure stability due to changes in focal length, especially when using ND filters, as they either require adjusting the aperture diameter or relying on gain circuits and electronic shutter circuits, which can introduce noise or reduce motion resolution.

Innovation Solution

An image capturing apparatus with a lens unit capable of changing focal length, an imaging unit, and a movable ND filter, controlled by a microcomputer to adjust the filter's position based on focal length changes, ensuring exposure stability by compensating for changes in aperture diameter and filter position.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the zoom magnification is controlled to the maximum (telephoto end), then the zoom magnification is improved, but the quantity of incident light is attenuated and the exposure is reduced

Engineering Contradiction:

Improvezoom magnificationVSAvoidquantity of incident light

Core Design Contradiction:

Adaptability or versatilityVSIllumination intensity

Solution Approach 1:

The patent changes the optical parameters of the system by introducing an ND filter that can be positioned at different locations in the optical path. By adjusting the focal length parameter and correspondingly adjusting the ND filter position, the system maintains exposure while achieving different zoom magnifications. The ND filter's optical density and position are varied to compensate for light attenuation during zoom operations.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If the aperture diameter of the diaphragm is opened to the maximum extent, then the minimum f-number is improved, but the exposure is reduced due to attenuation of incident light at telephoto end

Engineering Contradiction:

Improveminimum f-numberVSAvoidexposure

Core Design Contradiction:

Manufacturing precisionVSIllumination intensity

Solution Approach 1:

The ND filter serves as an intermediary element in the optical path between the diaphragm and the image sensor. It mediates the relationship between aperture setting and exposure by providing additional light density control. The microcomputer controls the ND filter's position to fine-tune the exposure independently of the diaphragm aperture setting, allowing the diaphragm to maintain its minimum f-number while compensation is achieved through the intermediary ND filter.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Illumination intensity

If the f-number is changed by the zoom magnification at aperture diameter greater than minimum f-number, then the exposure is maintained, but the f-number changes throughout the entire aperture diameter

Engineering Contradiction:

ImproveexposureVSAvoidf-number

Core Design Contradiction:

Illumination intensityVSManufacturing precision

Solution Approach 1:

The patent segments the exposure control function into two independent parts: the diaphragm aperture control and the ND filter position control. This segmentation allows the diaphragm to maintain a constant aperture diameter (and thus constant f-number) while the ND filter's position is adjusted to compensate for zoom-induced exposure changes. By dividing the control functions, the system maintains both exposure stability and f-number consistency simultaneously.

Inventive Principle:

Principle #1Segmentation

4Illumination intensity

If the size of the aperture diameter of the diaphragm is controlled to correct the f-number, then the exposure is maintained, but the state of the ND filter changes and causes prominent exposure change

Engineering Contradiction:

ImproveexposureVSAvoidexposure change due to ND filter state change

Core Design Contradiction:

Illumination intensityVSObject-generated harmful factors

Solution Approach 1:

Instead of controlling the diaphragm aperture to maintain exposure (which causes ND filter state changes), the patent inverts the approach: it keeps the diaphragm aperture constant and instead controls the ND filter position to maintain exposure. This inversion eliminates the harmful interaction where diaphragm adjustment causes ND filter state changes, because the diaphragm is no longer being adjusted. The ND filter becomes the active compensation element rather than a passive component affected by diaphragm changes.

Inventive Principle:

Principle #13The other way round (Inversion)

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 suppresses exposure changes during focal length adjustments, maintaining image quality without introducing noise or reducing motion resolution, by dynamically controlling the ND filter's position and aperture diameter.

Implementation Method 1

a filter (ND filter 7) capable of moving in a direction of insertion to an optical path of the imaging unit and in a direction of retraction from the optical path

Methodology Applied

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

Data Source

PatentUS8995826B2Image capturing apparatus and control method of the image capturing apparatus

Publication Date: 2015.03.31 CANON KK

AI summary

An image capturing apparatus comprises: a lens unit capable of changing a focal length; an imaging unit that outputs an image signal according to light incident through the lens unit; a filter capable of moving in a direction of insertion to an optical path of the imaging unit and in a direction of retraction from the optical path; and a control unit that controls a position of the filter using information related to the focal length of the lens unit.