ISO 8576
Definition
The ISO standard governing the accuracy of stage micrometers and reticle eyepieces, specifying Class I and Class II tolerance levels traceable to national length standards.
- Standard body
- ISO
- Applies to
- Stage micrometers, reticle eyepieces
- Tolerance classes
- Class I and Class II
- Traceability
- National length standards
Common questions
Why does a microscope calibration need a formal standard?+
Measurements made under a microscope, such as toolmark or trace fibre widths, are only defensible in court if the reference scale used to calibrate the eyepiece is itself traceable to a known length standard. ISO 8576 sets the tolerance the stage micrometer must meet for that chain of traceability to hold.
What is the practical difference between Class I and Class II?+
Class I devices carry a tighter permitted deviation from true length than Class II, so a lab doing fine comparison work such as striation matching typically specifies Class I equipment, while routine screening can tolerate the wider Class II band.
Related terms
- Abbe Diffraction Limit
- The minimum period of a periodic grating structure that can be resolved: d = lambda / (2 NA). Sets the hard optical...
- ASTM E766
- The ASTM International standard practice for image-scale calibration in microscopy, extended by OSAC to govern optical microscope calibration in US forensic trace-evidence...
- Depth of Field
- Axial thickness of the specimen that appears acceptably in focus at one time. High in stereoscopic microscopes, very low in oil-immersion compound...
- Empty Magnification
- Magnification beyond approximately 1000 times the objective NA; enlarges the image without adding resolvable structural information, producing blurred detail that can be...
- Infinity-Corrected Optics
- An objective design in which the back focal plane produces a collimated (afocal) beam rather than a converging beam, allowing optical elements...
- Koehler Illumination
- The standard illumination method for research microscopy in which the light source is focused at the condenser back focal plane, producing uniform...
- Numerical Aperture (NA)
- The product of the refractive index of the medium between objective and specimen and the sine of the half-angle of the maximum...
- Parfocality
- The property of an objective nosepiece turret such that switching objectives keeps the specimen approximately in focus without re-focusing; defined by ISO...
- Plan Objective
- An objective corrected for field curvature so that the entire image field is simultaneously in focus; required for photomicrographic evidence documentation to...
- Rayleigh Criterion
- The condition that two point sources are just resolved when the central maximum of one Airy disc coincides with the first minimum...
- Stage Micrometer
- A calibrated glass slide with a ruled scale of known spacing (typically 0.01 mm divisions), used to establish the pixels-per-micrometre calibration factor...