Stolze Stops

[Marc James Small <msmall@roanoke.infi.net>]

The European scale was developed by Franz Stolze (1830-1910).  It properly runs:

1.1-1.6-2.2-3.3-4.5-6.3-9-12.5-18-25-36-50-71-100

while the International scale properly runs with apertures half-way in
between these figures:

1-1.4-2-2.8-4-5.6-8-11-16-22-32-45-64-90

Leitz designed their longer lenses to have sufficient coverage for use as MF
and LF lenses, so they included the smaller apertures which are all the rage
with LF photographers.  

Zeiss used International apertures from at least before World War I, but
most other European manufacturers used the Stolze scale at least until the
Second War.  Voigtlander converted immediately prior to the outbreak of that
conflagration, but Leitz did not change over until the mid or late 1940's.
When they did so, they would remark the lenses as closely as possible, the
smallest aperture on a 4/90 Elmar, for instance, becoming f/32 in place of
the earlier f/36, though the lens, throughout its production life, could
still be moved just a tad PAST f/32 to reach that now-unmarked f/36.

Minimum apertures are, of course, also controlled by diffraction effects,
which is why so many uncoated lenses have surprising fast minimum stops.
For the first decade of its existence, the 1.5/50 Sonnar could only stop to
f/8, and even the earliest coated lenses only stopped to f/11.  It was not
until full coating became the norm that Zeiss reworked this lens to stop
down to f/22.  Many Leica lenses to this day, even new construction, only
stop to f/16.

Marc

msmall@roanoke.infi.net  FAX:  +540/343-7315
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