Put a Helios 44-2 on a Fuji body and it stops being a 58mm lens, at least as far as framing goes. It frames like an 87mm. On an Olympus Micro Four Thirds body it frames like a 116mm. Same glass, same aperture ring, very different lens in practice. Most of the confusion around adapted glass comes from mixing up three separate things: what the sensor crops, what the adapter has to do mechanically, and what a focal reducer changes.

There is something pointed about mounting a 1970s Olympus OM-System 50mm f/1.4 lens onto an OM System digital body four decades after the original system was discontinued. The Olympus OM mount, discontinued in the 1980s when Olympus moved to autofocus, left behind a generation of lenses that are available cheaply on the secondary market and adapt to Micro Four Thirds via a $20 OM-to-MFT adapter without optical compromise. On the E-M10 IV, the company’s most accessible current body, the old glass completes a circle that the company’s rebranding as OM System seems designed to acknowledge.

Wildlife and bird photography has a reach problem. Subjects do not cooperate with proximity, environments punish heavy equipment, and the focal lengths required to fill a frame with a distant bird in flight push into ranges where cost and weight traditionally become prohibitive. The OM System OM-1 Mark II with the M.Zuiko Digital ED 150-400mm f/4.5 TC1.25x IS PRO solves this problem in a way that nothing else in the market currently replicates.