[Leica] test for film speed

[Erwin Puts <imxputs@knoware.nl>]

You can not test for accurate film speed by using the greycard and exposing
it as a mid gray.
The correct way is this one:
Take a close-up picture (or as close as you can) from the grey card: expose
as the meter indicates (reflection from the M or any handheld meter. NOW;
take a series of pictures everyone one stop more under exposure. Five in
total. So assume the greycard reading is 1/125 at f/8 take a series with
A: lens cap attached and
B: 125/8, and
C: 125/11 and
D: 125/16 and
E: 250/16 and
F: 500/16 and
G: 1000/16
Develop as you wish or have been advised to do.
The negative exposed with 500/16 should have a very light grey density,
visibly above fog level (this you see in the negative with lens cap. If
that is the case your EI value is equivalent to the ISO value. Most often
you will see that this F neg  is also blank (only fog level). Then you
should look at the E neg: has this one some density, you should lower your
EI setting by 1/2 to 1 stop. If you are not interested in deep shadow
details, just proceed with the higher  setting.

Erwin