Bausch & Lomb Coddington Loupe
Bausch & Lomb Coddington Loupe
A classic single-element magnifier and its place in gemmological history
The Bausch & Lomb Coddington loupe is a single-element magnifying instrument based on the Coddington lens design, manufactured by the American optical firm Bausch & Lomb. Long regarded as a reliable and compact field tool, it occupies an important place in the history of gemmological instrumentation, bridging the era of simple hand lenses and the corrected triplet loupes that now dominate professional practice.
The Coddington Lens Design
The optical principle underlying this loupe was developed in the nineteenth century and is associated with the English mathematician Henry Coddington, who described a thick spherical lens with a groove cut into its equatorial plane. That groove acts as an internal stop, blocking the peripheral rays most responsible for spherical aberration and coma. The result is a single piece of glass — rather than a cemented assembly of multiple elements — that delivers a noticeably sharper and more rectilinear image than an ordinary biconvex hand lens of comparable magnification. Because the entire optical system is contained within one robust element, the design is mechanically simple and resistant to the separation or delamination that can afflict cemented doublets in humid or high-temperature conditions.
Bausch & Lomb's Instrument
Bausch & Lomb, founded in Rochester, New York in 1853, became one of the foremost optical manufacturers in North America, producing microscopes, binoculars, and precision loupes for scientific and trade use. Their Coddington loupe was offered principally in 10× and 14× magnifications, housed in a folding nickel or chrome-plated mount that protected the lens when not in use. The 10× version aligned conveniently with the magnification standard later codified by the GIA and adopted by the trade for grading diamond clarity — a factor that contributed to the instrument's widespread adoption among mid-twentieth-century jewellers and gemmologists.
The build quality of the Bausch & Lomb version earned it a reputation for durability. The lens, ground from a single piece of optical glass, was less susceptible to internal fogging than early cemented triplets, and the folding mount was robust enough for daily bench use. For several decades it was among the most commonly encountered loupes in North American jewellery workshops and at gem shows.
Optical Limitations
Despite its historical standing, the Coddington design has inherent optical constraints that distinguish it from the corrected triplet loupe now considered the professional standard. Because it relies on a single refracting element, it cannot fully correct chromatic aberration: white light is dispersed into its constituent wavelengths to a degree that produces slight colour fringing at the edges of inclusions or facet junctions, particularly at 14× magnification. The usable field of view — the central zone in which the image remains acceptably sharp — is also narrower than that of a well-made triplet, requiring the practitioner to centre the area of interest carefully beneath the lens. At higher powers these limitations become more pronounced, which is why the design was not commonly extended beyond 14×.
For routine inclusion examination, colour assessment, and surface inspection at 10×, these shortcomings are modest and many experienced gemmologists worked effectively with the instrument for decades. However, for the precise clarity grading of diamonds or the detection of subtle treatment features, the superior chromatic and spherical correction of a quality triplet loupe offers a meaningful practical advantage.
Place in Contemporary Practice
The Bausch & Lomb Coddington loupe is no longer in active production in its classic form, and the broader market has shifted decisively toward achromatic and aplanatic triplet loupes — instruments in which three cemented lens elements correct both chromatic and spherical aberration across a wide, flat field. The GIA, AGTA, and most professional gemmological bodies recommend the 10× triplet loupe as the standard tool for gem examination and grading.
The B&L Coddington nonetheless retains value as a collector's instrument and as a point of reference in the history of gemmological tools. Vintage examples in good condition are occasionally encountered at estate sales and among older jewellers' estates. For students of gemmological history, examining a Coddington loupe alongside a modern triplet provides a direct, instructive comparison of how optical correction technology evolved over the twentieth century.