It's a member of the prestigious "C/D P" family of lenses, made by Tokina for Soligor, and meant to be top-of-the-line, solidly built, fast alternatives to the Series 1 primes sold by Vivitar.
The red "P" could stand for "Pro", or maybe define the kind of coating being used, and is used only in four or five primes, all made by Tokina, with very good construction and modern (for the time) optical layouts.
The 2/28mm is the last lens I purchased, so I still have no opinions about its optical qualities, though I can say it's a gorgeous lens with a beautiful build.
I already had the most renowned member of the "C/D P" family, the 2/135mm, which is my favorite high speed 135mm, and a lens I always try to bring with me for portrait use on FF.
Both lenses I own are in M42 mount. There is no PKA version I'm aware of, but I would prefer to have the PK bayonet instead of the screw mount... I like to mount and remove lenses as quick as possible
The other members of the prestigious "C/D P" family I've seen are the 55mm Macro and the 2.8/200mm. There is another 2.8/200mm in the C/D line, but has no red "P", and was made by Sun Optical.
In another forum someone suggested the presence of another one, a 2/100mm, but I believe that lens predates the C/D (Computer Designed) series.
I own another very similar lens of the C/D line, also made by Tokina. It's the 2.8/100mm Macro. The construction is similar, but there is no red P.
I absolutely love the best Soligor primes, like the old super fast preset teles, or the best examples of the C/D line. I will try soon the 2/28mm, it is said to be prone to flare but with a beautiful rendering of out-of-focus areas.
Cheers
Paolo
---------- Post added 18-07-18 at 01:29 PM ----------
Originally posted by Jonathan Mac AFAIK all the Komine-made and Kino-made Soligor's predate the C/D line. All those I've seen are either Sun or Tokina.
Regarding other 2/28mm, well... as always happens when vintage lenses are involved, it depends very much on the state of the single examples.
I believe that a specific example of the Vivitar/Komine might beat a Vivitar/Kino (or its Kiron equivalent), but I have seen the test charts published at the time by major photographic magazines: the Kiron 2/28mm (and its 2/24mm sibling) stand out with impressive figures, even compared with well regarded OEM optics made by the "big brands".
The Komine is a very interesting lens though. A fast 28mm with close focus capability allows for some very creative framing
Each lens can find its use. Even the Mitake (Spiratone), which isn't the sharpest, has a very artsy bokeh