Confocal Microscopy
Definition
An optical technique using a pinhole aperture to eliminate out-of-focus light; by scanning through focal planes, builds a 3D height map of the specimen surface at sub-micrometre resolution.
- Key element
- Pinhole aperture rejects out-of-focus light
- Output
- 3D surface height map
- Resolution
- Sub-micrometre
- Application
- Tool-mark comparison microscopy
Common questions
What advantage does confocal microscopy offer over standard optical microscopy for tool-mark work?+
Standard optical microscopy flattens depth information into a single focal plane, while confocal scanning through multiple focal planes reconstructs an actual 3D surface topography. This lets examiners compare the depth profile of striations, not just their appearance under lighting, which is more resistant to angle-dependent visual bias.
Why does the pinhole aperture matter to the resulting image?+
Without it, light scattered from planes above and below the current focal depth would blur the image and mask fine surface detail. The pinhole blocks that out-of-focus light so each scanned point contributes only in-focus signal, which is what makes sub-micrometre resolution achievable.
Related terms
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- Comparison Microscope
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- Evofinder
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- NBTRB (NIST Ballistic Toolmark Research Database)
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- NFI (Netherlands Forensic Institute)
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- OSAC
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- SWGMAT
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