Parfocality

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...

ISO 8576

The ISO standard governing the accuracy of stage micrometers and reticle eyepieces, specifying Class I and Class II tolerance levels traceable to...

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...

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...

Explained in

• Microscopy Fundamentals: Magnification, Resolution and NAThe property of an objective nosepiece turret such that switching objectives keeps the specimen approximately in focus without re-focusing; defined by ISO 1093...