Olympus Zuiko Auto-S 40mm f/2

Wide open at f/2 the center is already crisp while the corners stay soft and the edges of the frame go dim. Stop down to f/4 and it tightens; by f/5.6 it is sharp across most of the frame. That is the trade Olympus made to keep it roughly 25mm deep, and once you know the curve you shoot around it.

The 40mm came out of Yoshihisa Maitani's drive to shrink the OM system. Every lens in that lineup ran smaller than the Nikon and Canon equivalents, and the 40mm f/2 pushes the idea to its limit: a pancake that barely clears the lens mount. Forty millimeters sits between the 35mm reportage view and the 50mm normal, a touch wide, the angle a lot of people find most natural to compose with. Olympus built it late, from 1984 into the mid-90s, and never in big numbers.

Rendering is classic Zuiko: neutral color, moderate contrast that holds shadow detail without going flat. Backgrounds go soft without nervous edges or harsh outlining around highlights. The multicoating handles a bright sky behind your subject without veiling, though a hard point source just off axis will throw a little flare. This is a street and travel lens first. It weighs almost nothing, so it stays on the body when a heavier prime would get left in the bag.

The honest problem is the price. It sits near the top of the OM price range and outruns many faster and longer Zuikos on the used market, riding cult status as much as its glass. You pay for the pancake form and the f/2 badge as much as the optics. The aperture ring is a thin band crammed onto the front, fiddly with gloves, and the corner softness wide open is real if you pixel-peep a landscape at f/2.

Cross-shop it against the other classic pancakes and the case clarifies. The Pentax SMC 40mm f/2.8, the Nikon 45mm GN, the Canon 40mm: all of them stop a full stop slower. The Olympus is the fast one. In a dim room, set Zone Light Meter to f/2 and you get a hand-held shutter speed those f/2.8 pancakes cannot reach, and the 49mm thread keeps filters cheap and shared across the small Zuikos. Whether the rarity tax is worth it comes down to how much you value carrying almost nothing.