OPL Gem Microscope — The Portable Field Instrument
OPL Gem Microscope — The Portable Field Instrument
A compact transmitted-light gemstone microscope by Optical Products Ltd, designed for portability and field use
The OPL gem microscope is a compact transmitted-light gemstone microscope manufactured by Optical Products Ltd (OPL), a long-established British supplier of gemmological instruments. The OPL diascope is designed for portability and field use rather than for the research-laboratory setting served by larger instruments from Leica, Zeiss, Olympus, or Nikon. It features built-in dark-field and bright-field illumination, typical magnification ranges of 10x to 40x, and a simple optical path with stand and stage that supports loupe-style and microscopic examination of inclusions, surface features, and basic gemmological identification.
Design and capability
The OPL diascope's design priorities — portability, reliability, ease of use — give it a defined place in the market alongside the more elaborate research-grade microscopes used in the major laboratories. The instrument is light enough to travel with a working gem buyer, robust enough to tolerate the conditions of an Asian or African gem market, and capable enough to support the routine identification and inclusion work that constitutes most field gemmology. Built-in illumination eliminates the need for separate lamp setups; the dark-field illumination is particularly useful for inclusion observation, where back-lit inclusions are highlighted against a dark background.
Magnification at the upper end (40x) is sufficient for most working identification tasks, including observation of healed fractures, growth structures, and most natural and synthetic identification features. Higher magnifications, when required, are typically achieved with a separate research-grade microscope rather than an extension of the field instrument. The OPL diascope is therefore best understood as a complement to higher-magnification laboratory work, not a replacement.
Illumination and inclusion observation
The dark-field illumination on the OPL diascope is its most useful feature for inclusion work. Light enters the stone from the side and at an oblique angle, so that direct light does not enter the optical path; only light scattered by inclusions and surface features within the stone reaches the eye, producing the characteristic dark-field appearance of bright inclusions on a dark ground. The technique is fundamental to inclusion-based gemstone identification and is essential for recognising the diagnostic features of natural and synthetic stones.
Bright-field illumination, also available on the OPL diascope, provides a different perspective: light passes directly through the stone, with inclusions appearing as dark features against a bright background. The two illumination modes complement each other, with dark-field generally more useful for general inclusion observation and bright-field providing additional information for some specific features.
Position in the market
The OPL diascope and its variants are favoured by travelling gem buyers, smaller commercial laboratories, gemmology students who need a personal instrument for coursework, and working jewellers who handle stones in sufficient volume to benefit from a dedicated microscope. Pricing is substantially below the major research-grade brands, and the instrument is widely available through the standard gemmological-supply channels.
For the purposes most working gemmologists encounter — confirming species identification, recognising treatment indicators, examining inclusions for origin clues — the OPL diascope is generally adequate. Research-grade microscopes from Leica, Zeiss, and the high-end specialist suppliers provide better optics, broader magnification ranges, and more sophisticated illumination options including polarised-light, fluorescence, and immersion-cell setups, but at multiples of the OPL price point. The choice between the two depends on the user's specific work and budget.
In the trade
For working gemmologists building a personal instrument set, the OPL diascope is one of the standard recommendations. Trade tool reviews in the gemmological press regularly cover the instrument and its variants, and the unit's long market presence has built a substantial user base whose feedback informs continuing product development. The instrument is also widely used in field-buying contexts where the combination of portability and adequate optics is more important than the absolute optical performance of a research-grade microscope.
See also OPL spectroscope, gemmological microscope, and dark-field illumination for related entries on instruments and techniques in field gemmology.