A Lens Collectors Vade Mecum list the Biotar as a "movie" lens with several patents for both 6 glass and 7 glass designs and suggest production was 6 glass/8 air surface.
The condensed serial number list shows 1928 ending at 908150 and 1929 starting at 919794 putting your lens in the gap between the years.
"Biotar f1.4 17, 20, 25,40,50mm,also a 70mm was due or reputed. It covers 42° (design
35-40°). 17, 20 and 25mm came later, the latter in some mountings such as Bell&Howell. (B.J.A. 1930,
p362). This was 'the latest introduction from --Carl Zeiss' in the B.J.A. 1929, p360. It was of 6-glass with 8 airglass
surfaces, and 35mm was needed for the 24x18mm of movie format, and 16.7mm for 16mm. This is an
angle of 42°. It was said to give excellent definition at f1.4, and maintains it on close down to f2, f3.5 and
smaller. It seems to have been introduced as 40mm (with 23mm clear back space) and 50mm for movie, and
25mm for 16mm, though 17 and 20mm were planned, and did in fact arrive.
Prices were 40mm £15.50; 50mm, £17.50; 25mm,£11.75.
There are references to 7 and 6-glass f1.4 Biotars in the Patent. It seems that the version sold was the 6-glass
from the examples seen. Those examined were at No 225,39x and 1,365,64x so this seems to be the norm. It
is given in Am. Photo. Facts and Figure 6th. Series, No 69 and in Hendley and Dudley, 1939) as 6-glass but
the 7-glass is shown in the Patent. So perhaps both layouts were used. It seems to be a 1927 design? (DRP
485,798 of 1927, Brit Pat. No 297,823, USPat 1,786,916/1930). (Layouts Zei026;Zei027). The glasses used
were G1+5+6=1.64238/48.0; G2= 1.62306/56.9; G3= 1.57566/41.2; G4= 1.67270/32.2."
Biotar f2.0 (Both Biotars f2.0 and f1.4 were designed by Merte.)
(Layout Zei031), B.J.A.1930, p363:1931, p318)
Note Some 50mm lenses have been found in a very heavy black enamel mount with M39 thread and these
just may be for M39 rangefinder use but may equally have been made for a movie camera with M39 thread.
They do trade expensively as Leica-fit items however. The serial numbers are early 1930's and they may well
have been an attempt to market the Biotar for Leica before the Leica patents were published. There are also
reports of later Zeiss lenses (not Biotars) in M39, but these seem to be very late 1930's or early 1940's items
made under "stress of war". Otherwise no use seems to be known for these f1.4 Biotars on still cameras, but
the B.J.A. 1939 p550 describes them as for "cine and miniature cameras" so something has perhaps been
missed.
