Exposure value

The exposure value in photography, often termed “EV” for short, is a technical term related to capturing the correct exposure in your images. It is a bit obsolete today due to digital cameras, but it’s a term that photographers should know when other photographers mention it.

While it’s not as fundamental to understand as the exposure triangle when it comes to exposure in photography, understanding the exposure value is still an important topic...

What is exposure value?

The Exposure Value (EV) in photography is a number that represents the combination of your camera’s shutter speed and aperture to achieve the right exposure.

For example, EV 0, EV 1, EV 2, etc.

The original intent behind the Exposure Value system was to simplify our selection of aperture and shutter speed combinations to yield the same exposure outcome under any given lighting condition.^[1] If we assign a single number (the Exposure Value) to each combination, we can easily switch between settings without changing our overall image exposure.

If you’re familiar with the exposure triangle, you know that it comprises our aperture, shutter speed, and ISO. So why is Exposure Value only about the relationship between shutter speed and aperture and not ISO?

Why ISO is excluded from exposure value calculations

Originally, when the EV system was developed, film cameras were the main cameras that photographers used, and changing the film’s ISO required changing the entire roll of film.

Because of this, ISO was considered to be fixed during the entire shoot, meaning you shot with that single ISO value the whole shoot. With that being said, the EV system was designed only around aperture and shutter speed, which were the variables that photographers could still readily adjust on the fly.

Of course, ISO plays a major role in our exposure settings nowadays, and it’s one of the three elements of the exposure triangle. But that's why the exposure value is only a combination of aperture and shutter speed values, not ISO.

As I'll show later, the exposure value chart and numbers are taken into account with a fixed ISO value of 100. But I'll be touching more on this in the next section.

Now, you can’t actually see the EV number anywhere on your camera, and it’s meant to be a calculation that you do, so let’s take a look at that calculation in order to get your Exposure Value.

How to calculate exposure value?

The basic formula for calculating the Exposure value is:

• N represents the aperture (f-stop number)
• t represents the shutter speed in seconds.

While it’s good to know what the formula is, you definitely don’t need to memorize this. Now, this formula gives us the Exposure Value for a given combination of aperture and shutter speed at ISO 100.

Increase in exposure value

The Exposure Value increases with either a decrease in the f-stop number (widening the aperture to let more light in) or a decrease in shutter speed (exposing the sensor to light for a longer time) and vice versa.

If we increase the EV by one step, such as EV 2 to EV 3, then we double the amount of light reaching the camera sensor, which is equivalent to a one-stop change in exposure.

Decrease in exposure value

The Exposure Value decreases with either an increase in the f-stop number (closing the aperture to let less light in) or an increase in shutter speed (exposing the sensor to light for a shorter time).

If we decrease the EV by one step, such as EV 3 to EV 2, we halve the amount of light reaching the camera sensor.

To better understand what all these words mean, let’s take a look at the Exposure Value chart.

Exposure value chart

Here is an Exposure Value (EV) chart I made that includes both negative and positive EV values, ranging from EV -3 to EV 15. This chart covers a broad spectrum of lighting scenarios, from very low light to extremely bright situations.

You don't need to memorize this chart, but it's a good reference to look at when I go through the examples later.

How to use exposure value in photography?

Now that we’ve seen the Exposure Value chart let’s see how we can use it and apply it to real-world photography situations. The way I like to categorize the Exposure Values is:

• EV -3 to EV 0 is for very low light conditions like dark or night landscapes
• EV 1 to EV 4 is for low light to indoor lighting
• EV 5 to EV 8 is for dim outdoor conditions to Golden Hour
• EV 9 to EV 12 is for bright indoor to overcast outdoor conditions
• EV 13 to EV 15 is for daylight to bright sunlight

Now, you may notice that the exposure value chart has some in-between numbers, such as 1/128 of a second for shutter speed. When using it in real life, you'll want to use the closest approximation of shutter speed, so in that case, it will be 1/125 of a second.

Here are some examples of EVs in real-world situations:

EV 15

EV 15 is good for a bright, sunny day with clear skies. Ideal settings might be f/16 aperture with 1/125 second shutter speed at ISO 100. This is often called the "Sunny 16" rule, a good starting point for daylight exposure without a meter.

EV 12

EV 12 is good for an overcast day or in the shade on a sunny day. You might use an aperture of f/4 with a shutter speed of 1/250 second at ISO 100.

EV 8

EV 8 is good for an indoor scene with window light or an outdoor scene during sunset. An appropriate setting could be f/4 with a shutter speed of 1/15 second at ISO 100.

EV 4

EV 4 is good for home interior lighting or dim outdoor conditions. You might choose an aperture of f/2.8 with a shutter speed of 1/2 second at ISO 100.

EV 0

EV 0 is good for night landscapes under the moonlight. A setting of f/2.8 with a shutter speed of 8 seconds at ISO 100 could be appropriate.

Once again, you may have noticed that I used ISO 100 for all of them because that's what the exposure value chart was based on. While the Exposure Value chart uses ISO 100, I wanted to finish this guide by showing what happens when we want to increase the ISO more than ISO 100 and how that affects our exposure value.

Balancing ISO with exposure value

As mentioned earlier, the computation of exposure value holds ISO at a constant value of 100.  But now that ISO is a major deciding factor in our exposure decisions, I wanted to show how you could pick an exposure value and then decide what it would change to if you raised the ISO.

Before we dive in, I want to recap our stops of light in terms of doubling or halving the light in our exposure. In case you aren't familiar with that term, stops of light refer to a measurement of doubling or halving the amount of light that makes an exposure.

So, increasing exposure by one stop means doubling the amount of light or making the photo twice as bright.

Decreasing exposure by one stop means halving the amount of light or making it half as bright.

Let's look at the stops of light in relation to our three elements of exposure.

For aperture (f-stop numbers), our full aperture stops are f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, etc.

For example, going from f/4 to f/5.6 would half the light:

Going from f/5.6 to f/4 would double the light:

For shutter speed, doubling the number would double the light, and halving the number would halve the light. For example, slowing the shutter speed by one stop from 1/100s to 1/50s would double the amount of light.

Speeding up the shutter speed by one stop from 1/100s to 1/200s would halve the amount of light.

For ISO, doubling the number would double the light, and halving the number would halve the light.

For example, increasing the ISO by one stop from ISO 100 to ISO 200 would double the light. Decreasing the ISO by one stop from ISO 200 to ISO 100 would halve the light.

Example: EV 15 in various lighting conditions

For my example, let’s take EV 15. So, let’s say we have f/16 at 1/125s at ISO 100, which gives us that exposure value of 15.

If we increase our ISO from 100 to 200, we’ll be adding 1 stop of light, making the image twice as bright.

To compensate for this change in ISO and to keep our same exposure value of 15, we would need to use the other two elements to darken the image to balance it out. We could either close the aperture or halve the shutter speed.

If we chose to close the aperture, we would close it to f/22, which would reduce it by 1 stop of light (f/16 → f/22). We would keep the shutter speed the same, resulting in f/22 at 1/125s at ISO 200.

If we chose to halve the shutter speed instead, we would increase it to 1/250s, which would reduce it by 1 stop of light (1/125s → 1/250s). We would keep the aperture the same, resulting in f/16 at 1/250s at ISO 200.

So, if we increased our ISO from 100 to 200, what if we wanted to change it to ISO 400? If we increase our ISO from 100 to 400, we’ll add 2 stops of light because 100 to 200 is 1 stop of light and 200 to 400 is 1 stop of light, so if we go from 100 to 400, that’s 2 stops of light.

This means we'll be making the image 4 times as bright. To compensate for this new change in ISO and to keep our same exposure value of 15, we could either once again close the aperture or halve the shutter speed, but twice now.

If we chose to close the aperture, we would close it now to f/32, which would reduce it by 2 stops of light (f/16 → f/32). We would keep the shutter speed the same, resulting in f/32 at 1/125s at ISO 400.

If we chose to halve the shutter speed twice, we would increase it to 1/500s, which would reduce it by 2 stops of light (1/125s → 1/500s). We would keep the aperture the same, resulting in f/16 at 1/500s at ISO 400.

This example illustrates the principles you should know by now, such as the exposure triangle, where ISO, aperture, and shutter speed work together to achieve a proper exposure for us.

If you don’t know these terms, then be sure to check out the exposure category and other videos I have on exposure. If all these numbers are confusing to you, just know that when I’m out on a photoshoot, I’m not sitting there in front of my clients with a pen and paper calculating the exposure value as I did in the example.

In conclusion, if you have a strong grasp of the exposure triangle, which is aperture, shutter speed, and ISO, and what each element does for your photo regarding exposure and creative effects, then that’s all you need to know.

As I mentioned in the beginning, understanding exposure value is not really that necessary these days, but it will level up your knowledge of photography and exposure, making you a better photographer overall!

So, I recommend familiarizing yourself at least a bit with the exposure value chart and knowing the common exposure values for real-world situations that I mentioned earlier. But the next time you hear exposure value or see it written somewhere, you now know what it means, why it’s used, and the history behind it!