Carl Zeiss Sonnar T* 135mm f/2.8 (C/Y)

Focus on an eye at f/2.8 and the background goes quiet. Out-of-focus highlights bloom into soft discs, and the handoff from sharp to unsharp happens gradually instead of snapping. Near wide open those highlights stay round and clean; stop down and they take on the shape of the diaphragm blades, which is just how a stopped-down aperture behaves. That smooth falloff is the thing this lens is known for, and it is why people who shoot Contax glass hang onto this 135 long after the rest of the kit is gone.

The design is a Sonnar, which explains the rendering. Sonnars give up a little edge resolution wide open in exchange for contrast and a certain roundness in the out-of-focus areas, and at a telephoto length that trade works in your favor for faces. Wide open it is already sharp in the center, plenty for skin and eyes, with a gentle softening toward the corners that nobody shooting a portrait will ever clock. By f/4 to f/5.6 the corners catch up and the frame tightens; by f/8 it is bitingly sharp across the whole field. The T* coating holds contrast and keeps flare in check even with the sun raking the front element, though the built-in sliding metal hood plus an extra deep shade still earns its keep when you are working into backlight.

Color is the other half of the signature. Zeiss C/Y glass leans saturated and faintly warm with deep blacks, and on slide film like Velvia or Provia that character is obvious at a glance. Reds stay rich without sliding toward orange, and the microcontrast gives faces a sense of depth on the page. This is glass built for the Contax RTS and Aria, manual-focus bodies aimed at people who valued how a frame looked over how fast it locked on.

The people who reach for it are portrait shooters chasing compression and subject separation without hauling a fast 85, plus street and documentary photographers who like working from a polite distance. The 55mm filter thread is unusually small for a 135, which keeps ND and polarizer costs down and trims the weight against its f/2 cousins. The honest catch is that f/2.8 is not f/2. If you want the thinnest possible depth of field, or the most light for handheld shooting in a dim room, the faster portrait teles pull ahead, and the long focus throw means you have to be deliberate about nailing the plane.

These turn up used well under modern Zeiss Milvus and Otus money, and shoppers tend to weigh them against the Canon FD 135mm f/2.8 and the Nikkor 135mm f/2.8. The Zeiss takes color and bokeh; the Japanese rivals take price and how easy they are to find. Metering it wide open in low light, remember the math runs off the f/2.8 maximum, so when you stop down, dial Zone Light Meter to your real working aperture rather than the marked one, and let it hold the reading off the subject's face so skin lands where you want it. For what these cost now, the rendering is a lot of lens for the money.