EV vs. f-stop
What is the difference between an EV and an f/stop? I have a Canon A2E which allows me to make +/- EV adjustments after the initial meter reading, but how does this differ from an f/stop?
I've read in my A2E manual that the camera supports 0-20EV. This makes me think it is a scale of light values, but how does this (if at all) correspond to an f/stop?
Does opening up a stop = +1 EV?!?
John A. Lind
The answer is YES.
Going to +1 EV increases the amount of light reaching the film by 1 EV and is the same (by definition of EV) as opening the lens up by a stop.
EV = Exposure Value
Your camera manual mentions it is capable of metering 0-20 EV, and probably mentions this is for ISO (or ASA) 100 film speed. It is the specification for the sensitivity range of your camera's meter.
The definition of EV:
Both definitions are "equal" to each other. It is how the brightness of the lighting and film speed translates to an aperture f-stop and shutter speed for a proper exposure. Change the aperture by one stop and you change the EV by one. Double or halve the shutter speed and you change the EV by one. Double or halve the film speed and you change the EV by one(for a proper exposure).
How to find the Av, Tv, Sv and Bv numbers:
You can probably find everything except Bv with a calculator, unless you have a very sophisticated light meter that measures light brightness in foot-Lamberts.
Exposure setting example:
For the extreme ranges of your camera with highest speed Canon lens, a 50mm f/1, the EV exposure range you can handle are:
Wide open at slowest speed:
Thus, if you put the absolute fastest lens you can (the 50/1) on your A2E, it has an EV range for setting exposures of -5 to 21 (spans 26 stops), which exceeds the 20 stop metering range! The most confusion about EV comes from thinking that EV is the level of lighting alone.
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