One of the questions I get asked most about photography is, “Why are my photos blurry?” It’s a good question because it gets right to the heart of photographic technique and deals with fundamental concepts like shutter speed, aperture, and ISO. In this post I’m going to talk about one of the most common causes of blurry images — motion blur. (Blur can also be caused by images that are out of focus and some people would call sensor noise a type of blur, but I’ll save those for another post) Before I dive into the exact techniques countering motion blur, I want to define a few basic terms.
Shutter Speed: The amount of time your camera’s image sensor is exposed to light is known as “shutter speed.” A fast shutter speed lets in less light but stops action better and a slow shutter speed does the opposite. On your camera shutter speed will show up as a number or fraction of a number. If your shutter speed is set at 10, that means your sensor will be exposed to light for 10 seconds (a slow shutter speed). If your shutter speed is set at 1/2000, that means your sensor will be exposed to light for 1/2000th of a second (a fast shutter speed).
Aperture: Out of the three terms we are discussing here, aperture is probably the most complicated. The reason for this is the aperture number (or f-number) displayed on your camera has an inverse relationship to what is actually going on inside the lens. But before we go into how aperture is controlled, we need to explain what it is.
While shutter speed is the amount of light allowed in by the camera body, aperture is the amount of light allowed in by the lens. This is controlled by a set of blades inside the lens that open and close to allow more or less light through the lens. See the photos below for an example. The first shows a lens “wide-open” or at it’s largest aperture. The second shows the same lens “stopped-down” to it’s smallest aperture.
Where this process becomes confusing is when you start dealing with how apertures are named. The “wide-open” photo above shows an aperture of f1.4, while the “stopped-down” photo shows an aperture of f22. The confusion being a “large” aperture (literally a large hole) is denoted by a small number and small apertures correspond to big numbers.
ISO: The “ISO number” (usually starting at 100 and going up) determines the sensor’s sensitivity to light. As the number gets higher, more light is absorbed by the sensor but this also causes images to appear noisy at higher ISO numbers.
(Because every camera is different, please consult your camera’s user manual for information on changing these settings.)
If it isn’t already clear, the main purpose of all three of the above terms is to control the amount of light in a photo. But changing one will likely have an effect on the others. If we were to look at this as a simple math equation, it would read something like this:
Light allowed in by the shutter + light allowed in by the aperture + light allowed in by the sensor (ISO) = total light in the photo.
Change one and you’ve changed the result unless you balance it by changing one of the other settings.
Fixing Motion Blur
To fix motion blur, first we need to know when we are dealing with motion blur. The telltale signs of motion blur include photos that look shaky, streaks of light, and an overall “smeary” appearance. If the photo looks out of focus, it probably isn’t motion blur.
Motion blur is caused when the camera’s shutter speed is not fast enough to capture the action. There are two main types of motion blur; one is caused by camera shake and the other is caused by objects moving too fast to photograph clearly.
As a general rule, camera shake becomes noticeable when the shutter speed drops below 1/100th of a second (although with telephoto lenses or when taking photos on the move, motion blur can occur at faster shutter speeds). With steady hands, it is possible to shoot photos with a shutter speed around 1/30th of a second but not much slower.
When a moving object is blurry but the rest of the photo is not, the problem is likely that the shutter speed is too slow to capture the movement. As an example; a shutter speed of 1/125th will capture people walking. A shutter speed of 1/500th will capture sports. A shutter speed of 1/1000th will capture moving cars. And a shutter speed of 1/2000th will capture motion faster than the human eye.
Fixing Motion Blur Option 1: As mentioned above, the easiest solution to motion blur is speeding up your shutter. But remember, the faster your shutter, the less light is getting into the camera. You’ll need to compensate for the loss of light by using a bigger aperture, a higher ISO number, or a combination of the two.
Fixing Motion Blur Option 2: If you subjects aren’t moving (family portraits, landscapes, etc.) put your camera on a tripod. The stability it provides is far better than even the steadiest of hands.
Tip: If your tripod has an extendable center column, generally avoid it. Extending the center column raise the center of gravity and detracts from stability.
Fixing Motion Blur Option 3: If your subject is moving and you can’t increase your shutter speed, try the photographic technique known as panning. This will blur the background but keep your subject sharp. To achieve this effect, you must move your camera with your subject. Most cameras will flip up the mirror or shut off the screen while they are taking a photo, so you will have to estimate the correct speed. This technique is simple to learn but hard to perfect.
Tip: Panning works best when your subject is moving perpendicular to your line of sight.
Fixing Motion Blur Option 4: If there isn’t enough available light to speed up your shutter and you can’t use a tripod, consider employing motion stopping technology like flash and image stabilization to cure your blur. Flash (from your camera or an external unit) will freeze motion and add more light to your photos. Lenses with image stabilization features will help correct camera shake but will not help you capture fast-moving objects.
(Have more questions? Something isn’t clear? Drop me a comment and I’ll do my best to answer!)