In photography, we talk a lot about "stop": it is the standard measure of exposure where an increase of one represents a doubling of the amount of light that strikes the sensor or film. One thing that many photographers do not realize is that the exposure actually has an absolute scale. Let me explain.
RELATED: What is a "stop" in photography?
Exposure values and stops
When you learn the basics of exposure triangle shutter speed, aperture and ISO it is important to know that there are several combinations of aperture and shutter speed that give the same exposure, even if the photo may look different because of your chosen aperture or shutter speed. For example, if you shoot a portrait outdoors and want a thorough depth of field, you might go with f / 2.0 for 1/ 2000th of a second; a few moments later if you instead decided to shoot a landscape, you can use f / 16 for 1/30 second. In both cases, exactly the same amount of light strikes as the sensor, so the light and the exposure of everything will be identical, but the images look completely different due to different apertures and shutter speeds.
But how do you know which combinations to use? Certainly you can go with trials and errors, but there is actually a final scale that is rarely taught. Both f / 2.0 for 1 / 2000th 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 as f / 8 for 1 / 125th of a second or f / 4 in 1 / 500th of a second.
And here is where things get smoother: an EV100 of 13 actually corresponds to some real light conditions. A cloudy day or the sky just before sunrise usually has an EV100 of 13, so a combination of aperture and shutter speed which also has an EV100 of 13 will work perfectly.
Why the exposure value is worth understanding
Before you go any further, I want to go back and explain why EV is worth understanding; It is unlikely that you will ever have to break out of EV tables to calculate which shutter speed to use while on a shot.
Instead, giving what an understanding of EV gives you a deeper understanding of what the camera does and why. I strongly believe that every photographer can benefit from knowing what happens to the camera when they press the shutter button. It is this kind of knowledge that lets you choose the right light meter or auto focus settings without just guessing.
For me, I learned about absolute exposure value also exposure clicks. All of this abstract call of stop suddenly ended a real, concrete meaning. I could understand why some combinations were equivalent. Then you do not know the need to memorize all the values in this article; Instead, just try to understand them.
The EV100 scale
The EV100 value of 0 is the combination of a f / 1.0 aperture and a 1 second shutter speed. Everything else is based on it. This means that your camera and lens can use EV100s between -1 and +21 without using any extra kit. This is one of the reasons why you need special equipment to take great pictures of the night sky that have an EV100 of between -3 and -11, depending on what the moon, stars and Aurora are.
Here is a full table of EV100 values from Wikipedia. It is a really good job to show which combinations of aperture and shutter speed match EV.
More interesting than I think to see how shutter speed and aperture match is to see what light levels correspond to what EVs. While the camera can go up to +21, you will not likely see EVs much higher than 16 in the real world.
|16||Snow on a sunny day|
|]|| Light clouds|