Oblique Scale Measurement for Optical Depth of Field

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Solution Overview

Problem

Existing methods for determining the depth of field in optical setups, such as microscopes, are inefficient and inaccurate, especially when objects cannot be easily placed or move rapidly, and autofocus or multifocus methods are not feasible due to focusing speed limitations.

Innovation Solution

A measuring device with a transparent body and oblique measuring scale that aligns with the optical axis, allowing direct and reproducible measurement of the depth of field without mechanical shifting, using a glass prism or slide with laser-engraved scale for precise reading.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a calibration pattern is shifted in depth using a precise shifting mechanism, then the depth of field can be determined, but the measurement process becomes time-consuming and complex

Engineering Contradiction:
Improvedepth of field determination accuracyVSAvoidmeasurement time
Core Design Contradiction:
Measurement precisionVSLoss of time

Solution Approach 1:

The measuring scale is pre-positioned at a known angle (e.g., 45 degrees) to the optical axis on the measurement object, eliminating the need for real-time mechanical shifting during measurement. This preliminary arrangement allows direct depth of field determination from a single image, resolving the contradiction between measurement precision and time consumption.

Inventive Principle:
Principle #10Preliminary action

2Speed

If autofocus or multifocus methods are used, then focusing speed can be improved, but they are not feasible for rapid moving objects or droplet sprays

Engineering Contradiction:
Improvefocusing speedVSAvoidapplicability to rapid moving objects
Core Design Contradiction:
SpeedVSAdaptability or versatility

Solution Approach 1:

The patent replaces mechanical focusing mechanisms with an optical measurement approach. By positioning a measuring scale at a known angle and capturing a single image, the system determines depth of field without mechanical movement, enabling measurement of rapid moving objects and droplet sprays that would be impossible with traditional autofocus methods.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

3Ease of operation

If a measuring scale is positioned perpendicular to the optical axis, then it is easy to read, but it cannot provide depth information

Engineering Contradiction:
Improvescale readabilityVSAvoiddepth information
Core Design Contradiction:
Ease of operationVSLoss of information

Solution Approach 1:

The measuring scale is positioned at an angle (e.g., 45 degrees) to the optical axis rather than perpendicular to it. This angular positioning adds a depth dimension to the otherwise two-dimensional scale reading. The known angle allows conversion of the scaled reading into depth information, simultaneously maintaining readability and providing depth measurement capability.

Inventive Principle:
Principle #17Another dimension (Dimensionality change)

4Measurement precision

If the measuring device is placed on the measurement object, then direct measurement is possible, but positioning and alignment become critical

Engineering Contradiction:
Improvedirect measurement accuracyVSAvoidpositioning and alignment requirements
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The measuring device is designed to be universally applicable to various measurement objects (microscope slides, flow channels, etc.). The scale is attached directly to the object surface at a known angle, making the object itself the measurement carrier. This eliminates the need for complex separate positioning and alignment mechanisms, as the object's own geometry provides the reference framework.

Inventive Principle:
Principle #6Universality (Multi-functionality)

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

Enables accurate and reproducible determination of the depth of field with minimal effort, eliminating mechanical displacement and reducing measurement errors, suitable for various optical setups including microscopes and flow measurements.

Implementation Method 1

the device body is optically transparent at least partially along the measuring axis

Methodology Applied
Scientific EffectRefraction: Refraction

Data Source

PatentEP4105594B1Measuring apparatus and method for determining a depth of focus of an optical structure
Publication Date: 2025.08.06 UNIVERSITAT STUTTGART
  • EP4105594B1 patent drawingFigure 1A~2
  • EP4105594B1 patent drawingFigure 3A~3C
  • EP4105594B1 patent drawingFigure 4~6

AI summary

The present invention relates to a measuring device (10) and a method for determining the depth of field of an optical setup (100). The measuring device comprises a device body (12) with a measuring axis (14), wherein the device body (12) is designed such that it can be placed in a stable position on a support surface of the optical setup in such a way that the measuring axis (14) of the device body (12) coincides with an optical axis of the optical setup, wherein the device body (12) has a measuring scale (18) applied along a scale line (16) such that the scale line (16) forms a scale angle ϕ greater than 0° and less than 90° with the direction of the measuring axis (14), and the measuring scale (18) is optically detectable by the optical setup (100) for determining the depth of field in the measuring position of the device body (12).