Lens speed is sometimes based on the shutter or barrel they are mounted in not the lens design.
https://www.schneideroptics.com/inf...arge_format_lenses/xenotar/data/2,8-80mm.html likely applies to your lens.
From A Lens Collectors Vade Mecum:
Xenotar
This was a 5-glass Gauss design, typically as in Sc034 and was or is an extremely high quality fast lens. It
has 2 single glasses in the rear and was made for a number of quite big formats up to 5x4in. A Schneider
sponsored article in Grossbild Tech. 1/1955 refers to the general concavity and deep curves of the surfaces
towards the diaphragm being a tremendous help in keeping low the angles of incidence of the light and
therefore the oblique aberrations of higher order could be kept to a minimum. These are big sharp lenses and
need very accurate focusing if they are to realize the full quality of the lens, and on cameras with cut film this
is not always obtained due to flexing of the film. Sc084 actually shows the drawing for a f2.8 80mm lens.
They were a lens used on the Rolleiflex models in f3.5 and f2.8 (B.J.A. 1954, p170), and some 6-glass
versions seem to have been made also. They do not cover a very wide angle so the 150mm is not suitable for
the use of movements on 5x4. It was new on Rollei in April 1953 and noted in MCM 5/1954. [This was about 1
year before the Zeiss Planar].
Xenotar f2.8 It was made in 80mm for 56x72mm =2.25x2.25in, 100mm for 65x90mm =
2.25x3.25in, possibly 135mm for 4x5in, and 150mm for90x120mm and 4x5in. When using the 150mm for
5x4in there is some freedom to use movements.
Some Xenotar 80mm lenses were sold to NATO in shutters, possibly for recording cameras. It was seen at
Nos 497571x (Rollei), 993788x on Linhof. It was used on Rolleis from April 1953. The 2.8E Rollei with f2.8
Xenotar [and Planar] was noted in B.J.A. 1957, p239. Another source of separate lenses can be Rolleis which
have suffered body damage and are written off as a result but where the lens can be salvaged and reshuttered.
The lens diagrams mentioned are
View attachment 191205
there is no Sc084 but Sc064 fits so the 8 may have been a typo
View attachment 191206