Minolta AF 135mm f/2.8 [T4.5] STF

Out-of-focus highlights from this lens have no outline. Near the diaphragm sits a concave element of neutral gray glass, thin and pale at its center, thick and dark toward its edge, and the light it dims hardest is the light that would draw the border of each blur circle. A streetlight behind your sitter still spreads as wide as an f/2.8 opening sends it, then thins to nothing instead of stopping at a bright ring. Minolta called this Smooth Trans Focus, and on the print there is no line where sharp turns into soft.

Geometrically the lens is an f/2.8, but the gray element stays in the light path at every setting, so it exposes like a T4.5, a stop and a third slower, with the gap narrowing as the iris closes down to the pale middle. Minolta built the lens around the T-number rather than pretend otherwise. Sony's manual for its later SAL-135F28 version says T-numbers are used for notation and control on lens and camera alike, and that for exposure the T-number stands in for the f-number of a normal lens. Zone Light Meter lists it the same way, as a T4.5 to T32 lens: take your reading at T4.5 and ignore the 2.8 in the name.

Mechanically it stands apart too. No other Minolta or Sony A-mount lens was made without autofocus, and no other carries an aperture ring. Leave the ring at A and the camera drives a nine-bladed iris in any exposure mode, down to T32. Off A, a ten-bladed second diaphragm takes over, set steplessly from T4.5 to T6.7 with faint clicks at T4.5, T5.6 and T6.7. Sony recommends this mode for wide apertures, where the gray element does most of its work. The camera then meters at the taking aperture; the manual says to work in aperture priority or manual, and warns that the aperture the body displays is no longer accurate, so read the setting off the ring instead.

None of this makes it a soft-focus lens. The plane of focus is crisp at full aperture, and the smoothing works on both sides of it, so a shoulder turned toward the camera blurs as quietly as the wall behind the head. Portraits are the obvious job, but the 87 cm close focus reaches a quarter life size, enough to fill the frame with a single bloom. Hohner lists eight elements in six groups with a floating focus design, all in a 730 g barrel that takes 72 mm filters.

Focusing is the hard part. It is entirely manual, on bodies built to do it for you, through a view only as bright as T4.5 allows, at a focal length where the sharp zone across a face is a few centimeters deep. Miss the eye and the beautiful blur is just blur. Low light is the other limit; in a dim room you pay for that gray glass with faster film or a push.

Minolta's own lens data puts the Japanese release at 19 December 1998, at 150,000 yen, though Hohner and Wikipedia both file it as a 1999 lens. Sony took over the design as the SAL-135F28 in 2006, when the list price was US$1,200, and later carried the idea to mirrorless, with autofocus, in the FE 100mm f/2.8 STF GM OSS. It has never been cheap, new or used. On a Maxxum film body the usual alternative is the 85mm f/1.4 G, more than three stops brighter wide open and with autofocus, which makes it the safer pick for children, weddings or anything that will not hold still.