In photography, we talk a lot about "stops": this is the standard exposure dimension, where increasing by one means doubling the amount of light entering the sensor or film. Many photographers do not know that the exposure actually has an absolute scale. Let me explain.
RELATED: What is a "stop" in photography?
Exposure values and stops
When learning the basics of the exposure triangle (shutter speed, aperture, and ISO value) It is important to know that there are several combinations of aperture and shutter speed that provide the same exposure, even if that Photo may look different due to the selected aperture or shutter speed. For example, if you're shooting an outdoor portrait and want a shallow depth of field, you might choose f / 2.0 for 1
But how do you know which combinations to use? Sure, you can go with trial and error, but there is indeed a final scale that has rarely been taught. Both f / 2.0 for 1 / 2,000th of a second and f / 16 for 1 / 30th of a second have an exposure value at ISO 100 (EV100) of 13. There are many other combinations that also have an EV100 of 13 like f / 8 for 1 / 125th of a second or 1: 500 for 1 / 500th of a second.
And here it gets even better: An EV100 of 13 actually corresponds to some real light conditions. A cloudy day or the sky just before sunrise generally has an EV100 of 13, so any combination of aperture and shutter speed, which also has an EV100 of 13, works flawlessly.
Why the Exposure Value is Understanding
Before You Continue I'd like to step back and explain why it makes sense to understand EV. It is unlikely that you will ever need to spread EV tables to calculate what shutter speed should be used during a recording.
Instead, understanding EV gives you a deeper understanding of what your camera does and what it does. Why? I'm convinced that every photographer can benefit from pushing the trigger when he knows what's going on with his camera. With this knowledge, you can choose the correct meter mode or autofocus settings without guessing.
For me, clicking the exposure value was an absolute must. All these abstract stops suddenly took on concrete meaning. I could understand why certain combinations were equivalent. So do not think about memorizing all the values in this article. Just try to understand them.
The EV100 Scale
The EV100 value of 0 is the combination of an aperture of f / 1.0 and a shutter speed of 1 second. Everything else is based on that. This means that your camera and lens can use EV100s between -1 and +21 without using an extra kit. This is one of the reasons why you need special equipment to take good photos of the night sky, which has an EV100 between -3 and -11, depending on where the Moon, Stars and Aurora are.
Here's a full table of EV100 values from Wikipedia. It does a really good job showing which combinations of aperture and shutter speed match which EVs. More interesting, I think, as to see how shutter speed and aperture match, one can see what the light levels correspond to the EVs. While your camera can reach +21, you probably will not see much more EVs than 16 in the real world.
|16||Snow on a sunny day  15||Sunny day|
|12||Cloudy, shady areas on a sunny day, sunrise and sunset|
|9 to 11||Just before sunrise and after sunset, the blue hour.|
|8||Bright street lighting, bright interior lighting|
|5 to 7||Interior lighting. Bright window light.|
|2 to 4||Darkened window light.|
|-1 to 1||Dark morning before sunrise, dark evening after sunset.|
|-2 to -3||Moonlight from the full moon.|
|-4||Moonlight from a lunar moon.|
|-5 to -6||Moonlight of Quarter Moon, bright aurora.|
|-7 to -8||Stars and starlight.|
|-9 to -11||Center of the Milky Way.|
The above table is a ballpark, but pretty much accurate. There will always be some variations, but if you follow it, you are not too far out there.
Using the Exposure Value
As I said earlier, understanding the exposure value for your photography is more useful in an abstract sense than in the practical sense, but that does not mean that you can not use it.
If you take long-exposure pictures with a neutral density filter, you can take your test shots without filters and then add the filter, add the stop value of the filter to the current EV, and use the help to find your new shutter speed the above EV card. You can also use an online EV calculator. This will probably be faster and you can also calculate EV values other than 100.
The other way to use EVs in the real world is the Sunny 16 rule. This rule states that when the outside temperature is sunny, the aperture is set to f / 16 and the exposure time for a correct exposure is 1 / [Your ISO]. So in our case 1/100. If you look at the graph, you'll notice that f / 16 has an EV100 of 15 for 1/100 of a second, which aligns nicely on a sunny day. The thing is, you can then use these as a basis to determine correct settings for other lighting situations. A lightly cloudy day needs f / 11 at the same shutter speed and ISO setting a single stop more. A very cloudy day requires a fade of 8, a heavily clouded day a fade of 5.6, and sunset light from a fade of 4.
You should always check your shots to make sure you do not miss your highlights blow it out When you crush your shadows, it's nice to be able to quickly guess the camera settings and be in the right park.
One of the main reasons why people have difficulty understanding the lighting is that they try to learn it abstractly. If you understand how exposure values relate to the real world, the concept is much easier to understand.