Abbe Diffraction Limit
Definition
The minimum period of a periodic grating structure that can be resolved: d = lambda / (2 NA). Sets the hard optical resolution ceiling for a given wavelength and numerical aperture.
- Formula
- d = lambda / (2 x NA)
- Governs
- Minimum resolvable grating period
- Field
- Optical microscopy
- Effect
- Hard resolution ceiling for given wavelength/NA
Common questions
How can a microscopist push past the Abbe limit for a given setup?+
Using a shorter illumination wavelength or an objective with a higher numerical aperture both reduce the limiting resolvable distance, since the limit scales directly with wavelength and inversely with numerical aperture.
Does the Abbe limit apply to every kind of microscopy used forensically?+
It applies to conventional diffraction-limited optical microscopy. Techniques such as electron microscopy, which use a much shorter effective wavelength, are not bound by the same optical ceiling.
Related terms
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- 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...
- 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...