Many photographers gloss over their camera’s exposure value scale. But it can help you capture the best possible exposure from any given scene.
Become an Exposure Value master and use it without thinking. The first step is reading this article.
What Is Exposure Value?
Exposure is the amount of light that reaches your sensor. A correct or proper exposure allows you to capture a scene without making it too light or too dark.
There are three camera settings that affect the exposure; ISO, shutter speed and aperture. This is without the use of a flash.
The exposure value in photography comes from all three working together. You might also know this as the exposure triangle.
When it comes to a scene, there are many ways you can come to the same exposure value with different settings.
For example, these four settings will give you the same image (in terms of light):
- ISO 400, SS 1/250th, Aperture f/8
- ISO 200, SS 1/250th, Aperture f/5.6 (ISO -1 stop, Ap. +1 stop)
- ISO 100, SS 1/125th, Aperture f/5.6 (ISO -2 stops, SS +1 stop, Ap. +1 stop, )
- ISO 100, SS 1/500th, Aperture f/2.8 (ISO -2 stops, SS -1 stop, Ap. +3 stops)
Why Would You Change Your Exposure Value Settings?
Digital cameras are far from perfect. They can record scenes really well, but depending on the scene you are shooting, it may have a hard time.
On top of this, you might decide that you want to capture the scene lighter or darker than the camera shows. This is where you use the exposure value in photography.
When you point your camera to an object, subject or scene, two things happen when you press the shutter release.
The first thing is your camera will focus. This only works if you don’t use back-button focusing, and if you are using AutoFocus.
The second thing is your sensor will ‘light meter‘ what is in front of your camera. This could be anything, and our cameras are geared for versatility.
When it comes to light metering, our cameras work from three modes: Matrix Metering/Evaluative Metering, Center-weighted Metering, and Spot Metering.
Each one of these looks at your scene differently. For more knowledge about these, check out our metering modes article.
The problems arise when you meter different areas of your scene. Photographing an urban landscape of sky and buildings might look great with the naked eye, but the camera will see it differently.
There can be up to two or three stops of light in shade-areas. So there will be a difference in the buildings compared to the sky.
If you place your meter focus on the sky, it will have a correct exposure, yet the buildings will be dark.
Vice versa is similar. If you meter for a correct exposure on the buildings, the sky will be blown-out.
This means it will be too light and will show little to no detail.
How To Calculate Exposure Value?
There is a relationship between the three main camera settings that deal with exposure.
- By changing your ISO, you directly influence image quality. A low ISO such as 100 will keep the quality and detail high, but it needs a lot of light in the scene.
- When you change your Shutter Speed, you allow motion blur. A fast shutter speed, such as 1/500th will freeze motion, but it needs a lot of light.
- Changing your aperture allows you to influence the depth of field within a scene. A slow or narrow aperture, such as f/16, will give you a very large depth of field, but it will need a lot of light.
Artificial light – neon lights at night 9 to 10 EV
Artificial light – from buildings at night 2 to 5 EV
Natural light – Golden hour 12 EV
Natural light – at night -2 to -11 EV
Natural light – snowy or sandy scenes 16 EV
Natural light – sunlight scenes on a clear day 12 EV
How to Use Bracketing for HDR?
Bracketing is a useful technique for ensuring you capture the correct exposure.
This technique was developed by film photographers, as they had no way to review their images. Better to have three than to rely on one shot.
Basically, bracketing would be to take 3, 5, or even 7 shots.
They are all odd numbers, as you need to take one image at the Exposure Value of ‘0’. This is what your camera tells you is the correct exposure.
From there, you are free to use +1/-1, +4/+2/-2/-4 or any combination. You could have +3/+2/+1/-1/-2/-3, for example, which will give you the slightest degree in light changes.
You can do it manually, but your camera needs to be set to manual mode. If you use programmed modes, Aperture Priority (A/AS) or Shutter Priority (T/TV), changing one setting will just change the other to balance the exposure.
These values need to be the same positive as they are negative. You won’t get a good range if you use -2/0/+3 for example.
If you decide to take three images with a two stop difference, your Exposure Values will be -2/0/+2.
This means you will have one image two stops darker, one image with an overall correct exposure and the last being two stops lighter.
For HDR or fused images, you can merge these differently exposed images together. The resulting image will contain detail from the highlights from the lighter image, and detail in the shadows in the darker image.
This is how we are able to capture the cityscape without blowing out the sky while retaining light in the shadow areas.
For more information on how to create these images, read our HDR from bracketing images post here.
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