Exposure Value (EV) – what is it and why so important?
Exposure Value is not a term that is used that much in photography. But understanding what it is and how it works is essential.
The term exposure, however, is used a lot and in a couple of ways. When a photographer says “I took one exposure of this landscape”, he means he took a photo of the landscape. He simply exposed the film or digital sensor to light and made the photo.
The more common use of exposure is to express the combination of shutter speed and aperture that is used when taking a photo. If the photographer say “the exposure was f16 at 1/125 of a second” at ISO 100, you can calculate the exposure value (EV) the camera uses.
I won’t bother you with the calculation because it is quite complex. And there is no need to know the formula either. But by experience I can tell with these settings, the image in the example was shot on a fairly bright sunny day.
The EV is given by a number. At any given light situation, there is a “correct EV” and a “creative correct EV”. How big or small the EV-number is something you don’t have to know. It is all taken care of by the camera. For you all is about aperture, shutter speed and ISO.
Correct Exposure Value (EV)
What is a “correct EV” is kind of subjective. Some photographers like the photos to have a slight dark feel to them. Most of us will agree an image should not be either too dark nor too light. We like the final image to look as similar as possible to what our eyes saw.
You have most likely experienced to get both too light and too bright images when you have taken pictures, definitely not what you intended.
A likely reason for this “bad” exposure was the aperture or the shutter speed was set to a wrong value according to the light conditions. Your camera did a wrong measurement because you allowed it to, or you chose the wrong settings yourself.
It is essential in photography to understand how you can fix exposure problems. Read on and I will explain how.
Creative Correct Exposure Value (EV)
The “creative correct EV” is when you take control of the camera and want to create special effects in a photo. Some of these effects can’t be seen with our eyes.
One example is when you freeze motion. You can “stop” the water in a waterfall so you can zoom in and look at the water drops in you photo. This is impossible with your bare eyes.
The other creative effect is the opposite and when you blur water and make it silky. This is also impossible for the bare eyes to see. I’ll explain soon how you can do this.
For both the “correct exposure value” and the “creative correct exposure value” there is one EV value that is right for the given effect considering the light is constant.
Three important settings for great result
Now you need to learn what aperture is. Aperture is a mechanism sitting inside the lens. You can see this as a little whole when you detach the lens from your camera and look through the lens.
The size of the opening can be adjusted allowing more or less light to enter. It is obvious the bigger the opening is, the more light hits the camera sensor.
Aperture values are given as f-numbers. What is not obvious is the lower the f-number is, the bigger the opening is. It is a little confusing, but you will soon get used to it.
The smaller the whole is (bigger f-number), the more depth of field you get. At f22 more of your picture will be in focus compared to f4 at the same focus distance.
In landscape photography, the aperture is an important setting because it is important to get the whole scene in focus.
The aperture scale
A common way of naming these figures are as f-stops. You might have heard the term stopping your lens up or down. When you stop down your lens you are decreasing the size of the aperture opening (rising the f-number). By doing this, you are changing the exposure value if you leave the shutter speed and ISO the same. The f-stop range differs from lens to lens. Read more about lenses and lens choices for landscape photography here.
Between each of the numbers shown here it is one f-stop difference. For example, if you change you aperture from f8 to f11 you will need the double amount of light for the same exposure value. Similar if you change from f8 to f5,6 you will need half the amount of light to keep the exposure value the same.
It is possible to use a half-stop and a one-third stop scale as well for more accuracy. For most of us the one-stop scale is fine. I hardly use the other scales. I make any such small exposure adjustments in Lightroom if I need to, this works just fine.
Next up is shutter speed almost as important as aperture. OK, they are equal important in general but to me as a landscape photographer, I am more concerned about the aperture. Well, let’s talk about the shutter.
The shutter is a mechanism sitting in the camera itself and not in the lens. You can think of he shutter as a curtain you can close and open.
Different from the aperture, there is no gradation of how much the shutter is open. The shutter is either completely closed or completely open. When the shutter is closed, no light hits the camera sensor. When it is open light enter through the lens and expose the sensor - a picture is made.
The way the shutter controls how much light is hitting the sensor is by adjusting how long it is open.
When the shutter speed is less than a second, shutter values are measured in fractions of a second. A shutter speed of 1/125s means one one-hundred-and-twenty-fifth of a second. In photography terms, 1/125s is a fairly normal shutter speed.
Shutter speeds more than a second is simply measured as whole seconds. You can set the shutter speed to several minutes in some situations.
By adjusting the shutter speed, you can blur or freeze movement.
Think about this for a second: When do you actually take a photo? Difficult question, right? If you read and understood what I wrote earlier on this page, you already know the answer. In fact, it is only when the shutter is open you take a photo. Taking a photo is when you expose the sensor to light. As you just learned this is only for a fraction of a second (normally).
On average I take 5000 photos per year. If the average shutter speed is 1/60 of a second, how much time do I spend taking photos every year? This is math… well, the answer is 83 seconds. That's less than two minutes per year. Funny huh?
By adjusting the shutter speed, you can blur or freeze movement.
As with the aperture, the difference between each number in the table above is one-stop. If you increase the shutter speed from 1/125s to 1/250s, you will need to double the amount of light to get the same exposure value. The same if you decrease the shutter speed from 1/125s to 1/60s you will need half the amount of light for the same exposure value.
On the shutter speed scale, it is a technical limitation on how fast the shutter can be. Some high-end cameras go all the way to 1/8000s - that's fast! 1/4000s is more common for most digital cameras. In the other end of the scale, 30s is the longest shutter speed you can set in most cameras. But it doesn’t stop there.
There is another setting named B (bulb). With this setting, you can expose for a very long time - up to several minutes. There is really no limit. But you need a cable release for that.
The shutter speed scale
- The orange figures can safely be used as long as you have enough light.
- The green shutter speeds are the most used when you are not doing creative shooting.
- The figures marked with red will require you to use a tripod to get sharp photos. The exception is if you want to achieve creative effect by using longer shutter speeds.
- The Bulb mode (blue) requires you to use a remote control on you camera
Finally, we have ISO. ISO is an international standard saying something about how sensitive your camera sensor is to light. The more sensitive the sensor is, the less light you need to get a proper exposure value.
ASA is the similar term for the sensitivity of film. In film days, you often chose the film based on what ASA value it had. When you loaded this film into the camera, the ASA value was set for the entire film. In general the higher ASA the film had, the more grain in the photos.
A digital sensor also has a given sensitivity (ISO) but as this is digital it is possible to increase the ISO electronically from its base level. This way you can set a different ISO on each photo if you want. It is unpractical and no reason to do so.
Increasing ISO introduces noise (grain) also on the digital sensor. How much noise varies from camera to camera. It is in low light situations you will want to increase the ISO. Some noise is better than not getting the picture at all. The flexibility with the ISO is one of the advantages of digital photography.
The ISO-scaleOn most digital cameras, the ISO ranges from 50 to 6400. Some extreme cameras reach all the way to ISO 128000. In general you want to set the ISO to the lowest possible setting on you camera.
Understanding exposure value is essential in photography. By mastering aperture, shutter speed and ISO you will be able to handle any lighting situation as a landscape photographer.
Knowing the relation between aperture and shutter speed opens for endless creative options, You don’t necessary need to memorize the figures, but doing so will make you more effective when you work in the field. After some training, it will be second nature.