Document Camera Focus Detection via Telephoto Zoom Shift

Solution Overview

Problem

Existing imaging devices face challenges with accurate focus detection, particularly when transitioning from wide-angle to telephoto zoom settings, due to deep or shallow depth of field issues, leading to defocus problems.

Innovation Solution

The imaging device includes a lens unit with a zoom lens and focus lens, where the focus position is detected while the zoom lens is positioned on the telephoto side of a predetermined reference position, allowing for more accurate focal position detection and eliminating the need for subsequent re-adjustment during zoom operations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If focus detection is performed at the wide-angle position, then the imaging range is broader, but the depth of field is too deep making focus determination difficult

Engineering Contradiction:

Improveimaging rangeVSAvoidfocus detection precision

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The system performs focus detection at the telephoto position where depth of field is shallow and focus determination is precise, then applies the detected focus position information to the wide-angle position. This preliminary detection at a favorable position resolves the contradiction by obtaining accurate focus data when telephoto and transferring it for use at wide-angle.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the zoom parameter (focal distance) during focus detection, performing detection at the telephoto position with shallow depth of field rather than at the wide-angle position. By changing this parameter, the system achieves precise focus detection and then maintains that focus setting across different zoom positions.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If focus detection is performed at the telephoto position, then the depth of field is shallow enabling precise focus detection, but the imaging range is limited

Engineering Contradiction:

Improvefocus detection precisionVSAvoidimaging range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The system performs focus detection at the telephoto position where depth of field is shallow and focus determination is precise, then applies the detected focus position information to the wide-angle position. This preliminary detection at a favorable position resolves the contradiction by obtaining accurate focus data when telephoto and transferring it for use at wide-angle.

Inventive Principle:

Principle #10Preliminary action

3Ease of operation

If zoom operation is performed after focus detection at wide-angle position, then imaging range can be adjusted, but focus shifts occur due to depth of field changes

Engineering Contradiction:

Improvezoom operation flexibilityVSAvoidfocus stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The system changes the zoom parameter (focal distance) during focus detection, performing detection at the telephoto position with shallow depth of field rather than at the wide-angle position. By changing this parameter, the system achieves precise focus detection and then maintains that focus setting across different zoom positions.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9007513B2Imaging device and method of controlling the same

Publication Date: 2015.04.14 SEIKO EPSON CORP

AI summary

A document camera has an automatic focus function, and performs the automatic focus process for automatically adjusting the focus lens to the focal position in accordance with the subject distance when the document camera is started up, or when the focus key of the input operation section is operated. Further, when performing the automatic focus process, the document camera is arranged to detect the focal position in the state in which the zoom lens is temporarily moved to the telephoto end with shallow depth of field, and then restore the position of the zoom lens to the original position.