[Leica] the F stops here

[calciua@hn.va.nec.com]

Dear Luggers,

we have discussed long and in detail the f-stop issue and the formulas and
data that passed along is right on (well, almost).

The numbers we have calculated do not apply to YOUR lens, but rather to the
mythical LENS in the sales brochure.

The reason is very simple. The F stop number is calculated by using the
focal length of your lens and the maximum aperture. Each lens has a
different focal length (your 50mm is probably 50.01345mm or 49.9845mm) and
the max aperture is not the one marked, but the actual maximum opening of
the iris (iris may open for instance to 20mm but the lens barrel may be
only 19.5 or vice-versa, the barrel may be 20mm, but the iris only opens to
19.32mm).

So, you see, without knowing the actual data for your lens, the number will
only be theoretical, not actual.

Of course, all this is immaterial, as the tolerances of the shutter and
latitude of the film make up for, or add to all these slight variations,
but it sure makes one feel more confident when he knows that one is off by
a precise amount :-)
_______________
Andrei D. Calciu
NEC America, Inc.
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