You may have heard photographers use the terms “exposure value” or “EV” when talking about the amount of light in a scene. But what does EV really mean in photography, and why does it matter to the photos you take? This article answers those questions and more.
Before I begin, I do want to mention that EV is a bit of a holdout in the modern world of photography, and not something you really need to calculate these days. I still think there’s a lot of valuable information you can take away from this article – and I wouldn’t have written it otherwise :) – but EV is more of a behind-the-scenes topic than the star of the show.
What Is Exposure Value?
Exposure Value (EV) is simply a way to combine shutter speed and aperture to a single value. Although shutter speed an aperture both carry a lot of “side effects” like motion blur and depth of field, EV doesn’t take those into account. EV only relates to exposure.
Calculating the EV for a particular combination of settings is done through this formula:
N is your f-number, and t is your shutter speed.
Unsurprisingly, there are many combinations of camera settings which yield the same EV. For example, the following two sets of camera settings…
- f/2.8 and 1/100 second
- f/4 and 1/50 second
…yield the same EV. Indeed, by following the formula above, you will find that the exposure value calculates to roughly 9.6 EV in both cases.
The EV Scale
The EV scales you’ll see most often tend to range from about -6 to +17. In theory, though, there’s no limit in either direction. For example, camera settings of f/22 and 1/4000 second yield an EV of almost 21 – though those settings are too dark for pretty much any real-world subjects (at least at ISO 100).
The “darker” your shutter speed and aperture (i.e. the less light you capture with them), the greater your EV. Hopefully, this makes some amount of sense; EV is often used to describe not just the camera settings you use, but also the brightness of the scene itself. A higher EV means you’re exposing for a brighter subject.
For a bright, midday scene, you’ll want a high EV like +15 or +16. In other words, you won’t want to capture too much light with your aperture/shutter speed combination.
For a dark subject – say, the Northern Lights – you’ll need a much lower value like -5 EV in order to avoid underexposure.
Here’s a table showing the EV of different shutter speeds and apertures:
|60 sec.||-6 EV||-5 EV||-4 EV||-3 EV||-2 EV||-1 EV||0 EV||1 EV||2 EV||3 EV|
|30 sec.||-5 EV||-4 EV||-3 EV||-2 EV||-1 EV||0 EV||1 EV||2 EV||3 EV||4 EV|
|15 sec.||-4 EV||-3 EV||-2 EV||-1 EV||0 EV||1 EV||2 EV||3 EV||4 EV||5 EV|
|8 sec.||-3 EV||-2 EV||-1 EV||0 EV||1 EV||2 EV||3 EV||4 EV||5 EV||6 EV|
|4 sec.||-2 EV||-1 EV||0 EV||1 EV||2 EV||3 EV||4 EV||5 EV||6 EV||7 EV|
|2 sec.||-1 EV||0 EV||1 EV||2 EV||3 EV||4 EV||5 EV||6 EV||7 EV||8 EV|
|1 sec.||0 EV||1 EV||2 EV||3 EV||4 EV||5 EV||6 EV||7 EV||8 EV||9 EV|
|1/2||1 EV||2 EV||3 EV||4 EV||5 EV||6 EV||7 EV||8 EV||9 EV||10 EV|
|1/4||2 EV||3 EV||4 EV||5 EV||6 EV||7 EV||8 EV||9 EV||10 EV||11 EV|
|1/8||3 EV||4 EV||5 EV||6 EV||7 EV||8 EV||9 EV||10 EV||11 EV||12 EV|
|1/15||4 EV||5 EV||6 EV||7 EV||8 EV||9 EV||10 EV||11 EV||12 EV||13 EV|
|1/30||5 EV||6 EV||7 EV||8 EV||9 EV||10 EV||11 EV||12 EV||13 EV||14 EV|
|1/60||6 EV||7 EV||8 EV||9 EV||10 EV||11 EV||12 EV||13 EV||14 EV||15 EV|
|1/125||7 EV||8 EV||9 EV||10 EV||11 EV||12 EV||13 EV||14 EV||15 EV||16 EV|
|1/250||8 EV||9 EV||10 EV||11 EV||12 EV||13 EV||14 EV||15 EV||16 EV||17 EV|
|1/500||9 EV||10 EV||11 EV||12 EV||13 EV||14 EV||15 EV||16 EV||17 EV||18 EV|
|1/1000||10 EV||11 EV||12 EV||13 EV||14 EV||15 EV||16 EV||17 EV||18 EV||19 EV|
|1/2000||11 EV||12 EV||13 EV||14 EV||15 EV||16 EV||17 EV||18 EV||19 EV||20 EV|
|1/4000||12 EV||13 EV||14 EV||15 EV||16 EV||17 EV||18 EV||19 EV||20 EV||21 EV|
|1/8000||13 EV||14 EV||15 EV||16 EV||17 EV||18 EV||19 EV||20 EV||21 EV||22 EV|
Hopefully there’s nothing too shocking in this chart. I just used the same formula from earlier to calculate EV’s for some of the most common aperture and shutter speed values. Still, I think it’s helpful to visualize like this, so you can see how changing shutter speed or aperture affects your exposure value.
I’d like to emphasize that each time you increase or decrease the EV by one value (or one “stop”), you are literally capturing half or twice as much light. An EV of 1, for example, captures quite a bit of light; an EV of 2 captures half that (which is still a lot); an EV of 3 captures half again. And so on.
The more interesting thing here is to figure out the relationship of these exposure values to real-world lighting conditions. For example – in what situations would an EV of 10 give you the proper exposure? Sure, you can get an EV of 10 using anything from 1/1000 second at f/1.0, all the way to 1/2 second at f/22 on the chart above. But when should you use one of those aperture/shutter speed combos?
That’s where a second chart comes in:
|EV||Real-World Situation for Proper Exposure|
|1This chart assumes ISO 100. Situations adapted from my own photos and from Wikipedia.|
|-6||Nighttime landscape under quarter moon|
|-5||Aurora borealis of moderate brightness|
|-4||Nighttime landscape under gibbous moon|
|-3||Nighttime landscape under full moon|
|-2||Nighttime snow or beach landscape under full moon|
|-1||End of blue hour|
|0||Late in blue hour|
|1||Middle of blue hour|
|2||Distant cityscape at night|
|3||Indoor scene lit only by dim window light|
|4||Floodlit monuments or fountains at night|
|5||Typical artificial indoor light|
|6||Bright indoor lighting|
|7||Fairs and theme parks at night|
|8||Bright window displays and advertisements at night|
|9||Nighttime sporting events under bright light|
|10||Moment after sunset on a clear day|
|11||Daylight on a foggy day|
|12||Moment before sunset on a clear day|
|13||Typical subject on a bright, cloudy day|
|14||Typical subject on a day with hazy sunlight|
|15||Full sunlight on a cloudless day, typical subject|
|16||Full sunlight on a cloudless day, bright subject (i.e. the beach)|
|17||Full sunlight on a cloudless day, highly reflective subject (i.e. snow)|
Obviously, there are more than just these 24 different lighting situations; I’ve only chosen one example per EV.
That’s why, rather than just taking the values above for granted, I recommend looking at your own images. Sort your photos by ISO 100 in software like Lightroom, and study various aperture/shutter speed combinations to see how the lighting conditions looked when you used those settings. You may find some interesting connections, like using the same settings to photograph (for example) the full moon with a telephoto as you did for a landscape on a sunny day.
I know I said that EV is a bit of a tangential subject to modern photography, but this is one case where it can lead you down a very useful path. By examining your own photos and figuring out which EV’s you used – and in what circumstances – you really will get a better understanding of how to expose your photos properly.
What About ISO?
You’ll note that the chart above assumes you’re at ISO 100, and I also mentioned ISO 100 briefly a couple other places in this article. What’s so special about that ISO?
Nothing, really. That’s just how the chart is calibrated – it assumes you’re at ISO 100 in every case. But you certainly can make a similar chart for any other ISO. For example, ISO 800 is three stops brighter than ISO 100 (because the ISO scale goes 100, 200, 400, 800). If you’re at ISO 800 when the chart assumes you’re at ISO 100, that’s a recipe for overexposure. To compensate, you’d need to shift the “real-world situations” up three spots in the chart.
That said, ISO 100 is the standard, and that’s what you’re almost certain to see in any EV chart online or in print.
Practical Applications of EV
One thing I always keep in mind when learning a new concept in photography is that it can be useful even when it’s not actually worth using.
I bring this up because EV definitely is not something most photographers think about in their everyday work today, nor a concept you need to understand in order to take proper exposures.
Even if in manual mode, most photographers choose their camera settings by looking at their camera meter’s recommendation, or by reviewing their histogram. Very few go through the whole process of looking at the scene, trying to estimate where it stands on an EV chart, and then finding corresponding aperture/shutter speed values for that EV. Aside from film photographers who left their meter (and now their phone) at home, there are better options than that.
Still, EV isn’t totally without practical applications – although most of them do fly somewhat under the radar. For example, you may have seen cameras advertised as metering or autofocusing down to “-4 EV” conditions (or -5 EV, -6 EV, etc.). In that case, EV is an important part of understanding a camera’s capabilities.
It’s also an area where a little knowledge can save you some money. Manufacturers like to fudge their EV numbers by using wide aperture lenses for their measurements. For example, a camera that can focus down to -6 EV conditions with an f/1.2 lens sounds very impressive – and it is – but a camera that can focus in -5 EV conditions with an f/2 lens actually is a bit better in low light (something that is obvious once you equalize the f-stops and shift the EV accordingly).
In the field, another application is simply to improve your “mental meter” and recognize when something may be wrong with your camera’s recommended exposure. If it’s a cloudy day, and your camera settings read something like f/8 at 1/4000 second, there’s a problem. Most likely, you accidentally bumped up your ISO too high.
The final real-world example I’ll give is when you’re shooting long exposures with something like a 10-stop ND filter. Going 10 EV’s up a chart like this will give you a set of potential aperture/shutter speed values to use – something that can be helpful if your meter isn’t working properly with the filter (especially as the light changes).
As I mentioned in our article on the sunny 16 rule, there really is no “useless” technique in photography if it deepens your understanding of things. That applies to exposure value just as well.
Despite its (relative) outdatedness, EV is still deeply tied to concepts like shutter speed, aperture, ISO, and proper exposure. By the time you understand all the ins and outs of exposure values, you’ll have learned the other, more relevant stuff simply by association.
Plus, if nothing else, the two charts in this article can act as a sort of sanity check to make sure your exposures are reasonable. It’s the world’s simplest and least flexible meter, but even then it’s almost always going to be in the ballpark of the proper exposure.
And that sums up exposure value! Hopefully this article gave you something to think about even if you don’t plan to calculate EV’s in practice. If you have any questions or comments, feel free to let me know in the comments section below.