Constant-aperture zoom lenses are usually a size tradeoff — maintaining the same f-stop across a zoom range typically means bigger glass. The M.Zuiko 12-45mm F4.0 PRO, launched under the Olympus name in February 2020 before the brand's transition to OM System, claimed the opposite: a genuinely constant f/4 aperture from 24mm to 90mm full-frame equivalent, in a lens under 3 inches long and just over half a pound.
Nine internal seals give it real dust and splash resistance despite the compact size, and a 0.5x maximum magnification at the telephoto end lets it double as a passable close-up lens without switching to a dedicated macro. Reviewers have consistently pointed to it as one of the best all-around standard zooms in the Micro Four Thirds system — not the fastest glass available, but the one most likely to actually get carried on a hike.
