EV as used on old cameras and lenses does not depend on ISO, only on shutter speed and aperture. You can calculate EV as follows:
For shutter speed (at aperture f/1):
1 second = EV 0
1/2 = EV 1
1/4 = EV 2
1/8 = EV 3
1/15 = EV 4
1/30 = EV 5
1/60 = EV 6
1/120 = EV 7
For aperture, (at 1 second exposure)
f/1.0 = EV 0
f/1.4 = EV 1
f/2.0 = EV 2
f/2.8 = EV 3
f/4.0 = EV 4
f/5.6 = EV 5
f/8.0 = EV 6
f/11 = EV 7
f/16 = EV 8
f/22 = EV 9
To get the EV corresponding to a particular shutter speed and aperture, simply add the EV I've listed for the shutter speed (at f/0) to the EV listed for the aperture (at 1 second). So EV for 1/120" and f/16 would be 7 + 8 = 15. This corresponds to the "Sunny 16" rule for ISO 120 film (since the shutter speed is 1/120"). So when you set EV 16 on the camera, if the built in shutter speed is fixed at 1/120" then you are simply setting the aperture to f/16.
Originally EV ("Exposure Value") only referred to the factors affecting exposure (shutter speed and aperture) and not to the film sensitivity. Later on, EV was used as a measure of light intensity. In this case, ISO 100 is usually assumed. You have to figure out from context whether a use of EV refers to an exposure setting (as it does with the camera) or a light intensity (as is the case with light meters calibrated in EVs).
So if you have a light meter calibrated in EVs (referenced to ISO 100) and you put ISO 100 film in the camera, then you can simply take the EV reading from the light meter and put it into the camera for a "correct" exposure. However, if you use a different ISO film then you need to adjust the EV reading from the light meter to account for the difference between the light meter calibration (usually ISO 100) and the actual film speed.
For example, with ISO 400 film, you need to decrease the exposure by 2 stops compared to ISO 100. To do this you have to ADD 2 to the EV since increasing the EV by one reduces (makes darker) the exposure by one stop. If the light meter reads EV 10, then for 400 film you would set the camera to EV 12.
Of course if the light meter includes an ASA setting (typically found on the calculator dial) then you may simply be able to set this to the ISO of the film you are using and then read the correct EV for that ISO from the meter, and then use it without any adjustment.
The fact that your exposure cards specifies EV 11.5 for a sunny day suggests it was designed for film that is about 3.5 stops slower than ISO 120, hence somewhere around ISO 10.6 (calculated as 120 / 2^3.5). According to Wikipedia, Kodachrome daylight film in that era was ISO 10. The Type A film was ISO 16, for use indoors under floodlights (presumably for movies).
Last edited by andrew.roos; 11-06-2012 at 11:22 AM. Click to view previous post history.