An objective lens is the primary image-forming optical element in an instrument — the lens closest to the object being observed or measured. For customs classification, the key factors are the lens's functional role within the instrument (image formation rather than eyepiece or relay function) and its design for use in apparatus such as microscopes, telescopes, or spectrometers. Technical datasheets and instrument assembly diagrams are the standard supporting documentation.

Parts and accessories specifically designed for objective lenses — such as lens barrels, retaining rings, or adjustment mechanisms — are classified together with the lenses under 9002190000 when imported separately, provided they are identifiable as parts of objective lenses for instruments. Generic mechanical parts without optical specificity may fall outside Chapter 90 entirely. When in doubt, a binding ruling from CBP provides the most reliable classification guidance.