I’m sure that if you ask 20 people for the definition of Exposure Value, half will give you a definition for Exposure Compensation while the other half will provide an answer to a question that you didn’t ask. In his book, The Betterphoto Guide to Exposure, Sean Arbabi writes the following definition about Exposure Value:
“… is a method that was created to simplify exposure combinations for certain measurements of light. The term is used throughout digital photography and can be a bit puzzling, since it’s applied in a variety of ways: to measure light, for incremental settings in your aperture or shutter speed, for your meter using exposure compensation and so on. If you get a little lost in this section, move forward and then refer back to it from time to time; as you learn more about exposure, EV may begin to make better sense.”
Now, if you’re new photography (like me), the aforementioned paragraph reads like a pile of horse poo! Yep. It went straight over my head. After MUCH research, I’ve found a better way of explaining it. Upon reading my definition, you’ll think, “Darn. That’s it?”
Exposure Value is a ‘nickname’. That’s right. It’s a nickname. Here’s an over-simplified non-photography related example: I have a good friend whose name is Linda Consuelo Epstein. Instead of calling her Linda Consuelo Epstein, we call her Linn; it’s easy to remember and suites her. Whenever someone says, “Hey Linn!” She knows that they are addressing her, because Linn, which is her nickname, is short for Linda Consuelo Epstein.
Here’s another over-simplified example: If someone asks me my daughter’s age, I COULD say, “Oh, she’s 1,239 days (exposure value)” or “She was born October(ISO) 7(Aperture), 2006(shutter speed).” The combination of ISO, Aperture, and Shutter speed is Exposure Value.
Now, don’t get me wrong, Exposure Value isn’t just ANY old combination of ISO, Aperture and Shutter Speed, it’s SUPPOSED to be the perfect combination of ISO, Aperture and Shutter speed for a given situation.
On a bright sunny day, if EV is 15, Aperture=f/16, ISO=100, and Shutter speed=1/125. How did I come up with that? I looked at the chart you ninny! No one in their right mind sits around and calculates this mess! NO ONE! EVERY ONE PULLS OUT A CHART! Could you calculate Exposure Value for yourself? Sure, but why bother? Your camera does it for you.
At this point you’re probably looking for the Exposure Value setting in your camera. Sorry but you’ll find not such thing, unless of course, you recognize that your camera’s meter is the modern day abacus for Exposure Value. That’s right, balance your camera’s meter and you’ve in essence, calculated the right exposure.
So the next question is probably, “Why are people making this out to be more than what it is?” The correct answer is either because they can, or they are confusing Exposure Value with Exposure Compensation. Exposure Compensation is the adjustment that you make to an Exposure. Let’s say you meter off your subject, and the perfect exposure is f/16, ISO 100 and shutter speed of 1/125 and you find that it’s too bright. Making an adjustment to underexpose the shot by a third of a stop (-.3) is Exposure Compensation.
In summary, Exposure Value is perfect combination of Aperture, ISO and shutter speed for a given situation. Exposure Compensation is the adjustment to that exposure.