I believe that I know. 85 is the journalists portrait grabber. Their "normal" may be a 35 so that 85 is quite a step up (vs when your normal is a 50). 85 is short and fast enuf for quick reportage style handheld "portraits", even in crappy light.

85mm is acoarst a Nikon FL. With Leica its 90. Note that I called it a "portrait grabber". Its not really a studio lens ... and anywho studio cameras are generally bigger. 85 and 90mm decend from rangfinder 35mm film kits. With RFs, the mechanical accuracy limited 105 and 135 lenses to slower max apperture, so 85 and 90 could be about a full stop faster than those longer lenses.

Thaz the story in broad strokes. Broad strokes !! I now step aside so as to not get trampled by a herd of nit pickers.

Always gotta wonder what Hawgsters actually mean when they say "portrait", altho all their parroting of "85, 85, portrait lens, 85, 85 ... " is a bit of a hint.

The function of an 85, relative to 50 and 35mm "normals" is to get a very slight shift toward longer lens perpective while not much demanding the usual long lens attention to increased steadiness and shutter speed.

Part of this is due to 85 being short enuf to share the lens speed typical of "normal" lenses while remaining fairly compact. A 105 f:1.8 is already a heavy bulky clunker, but an 85 f:2.0 looks like a 50 f:2 that grew a 1/2 inch longer.