Carl Zeiss Planar T* 50mm f/1.7 (C/Y)

Shoot a backlit portrait at f/2 with a window blowing out behind the subject, and watch what the T* coating does that uncoated and single-coated fifties cannot. There is very little veiling haze creeping across the face, and the blacks hold up with the light source right in the frame. Point a cheaper double-Gauss at the same window and you get fog. The Planar isn't immune (put the sun directly in the corner of the frame and you can still catch minor ghosting), but for a design this old the flare resistance is the thing that keeps it on cameras.

This is the budget Planar in the Contax/Yashica line, the one that lived under the f/1.4 in every catalog and got treated as the kit lens. That reputation is unfair. The optical formula here is a double-Gauss derivative, seven elements in six groups, descended from the classic symmetric six-element layout but not identical to it. Wide open the center resolves well, but microcontrast is modest. Stop down to f/2.8 or f/4 and the small tonal steps that give the so-called three-dimensional pop come alive. It's genuinely sharp by f/2.8 and bitingly resolved across the frame by f/5.6. Skin, fabric texture, the edge of a jaw against a soft background all start to separate and sit forward in the image once you're past the maximum aperture.

Bokeh changes character with the f-stop. Wide open, out-of-focus highlights carry a well defined edge and the rendering runs busier than the f/1.4 on cluttered backgrounds. By f/2.8 it cleans up, the falloff turns smooth, and highlights stay round near the center while going lemon-shaped toward the edges. Contrast runs higher than a Nikkor or Takumar of the same era, color is neutral with a slight warmth, and the look is crisp without tipping into clinical. One thing to know going in: it shows noticeable M-shaped field curvature wide open, so off-center subjects can land on a different focus plane than the center. That flattens out as you stop down, and by f/8 the corners on a landscape are excellent.

The weakness is the one you'd guess from the name. It's an f/1.7, not an f/1.4. You give up two-thirds of a stop of light and a sliver of subject isolation, and in a dim room that gap matters. If you want the shallowest separation or the absolute most light, the f/1.4 Planar exists for a reason. But the 1.7 is smaller, lighter, and costs a fraction of what the 1.4 commands, which is most of why people end up with it.

Right now it's about the most affordable honest route into the Zeiss rendering. People cross-shop it against the Contax 50mm f/1.4, the Olympus Zuiko 50mm f/1.8, and the Nikkor 50mm f/1.8, and the Planar holds its own on rendering against all of them. It mounts cheaply on mirrorless with a C/Y adapter, which keeps demand alive. When you do work it wide open in low light, meter for the shadows you actually want to keep and let Zone Light Meter place them rather than trusting an averaged reading, which on a contrasty lens like this will routinely clip the highlights you came for. The 55mm filter thread is shared across much of the C/Y prime set, so one set of NDs covers the kit.