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Shutter Speed

August 2, 2011

In my previous post I described what the aperture setting on a camera does. Today I will explain shutter speed.

The shutter is a mechanical device in the body of the camera, whereas the aperture is actually in the lens. Quite simply, the shutter opens and closes in order to expose the image sensor to light. The amount of time the shutter stays open is part of what determines the exposure of an image. In lower light situations, the shutter needs to stay open longer in order for enough light to accumulate on the sensor and make the proper exposure. Conversely, more light means that the shutter does not need to stay open as long.  Shutter speed works hand in hand with the aperture setting and the ISO setting to determine a proper exposure for a photo.  Wider apertures (more light entering the camera lens) and higher ISO settings (light sensitivity of the image sensor) will allow you to use a faster shutter speed which is usually desireable in order to avoid blurry photos from camera shake or motion in the scene.

Here is a photo of a the shutter mechanism from a Canon 5D mk II camera.

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When slower shutter speeds are used, you run the risk of having blurry photos when hand holding the camera, because even the slightest movement can cause camera shake. A good rule of thumb to avoid camera shake is to use a shutter speed that is 1/focal length. For example, if you are shooting with a 50mm lens, you would want to choose a shutter speed of at least 1/50 of a second. Of course, that shutter speed may still not be slow enough to make a proper exposure. In that case, you may need to choose a wider aperture or raise the ISO. (I will talk about ISO in the next post). Doing one or both of these will allow you to shoot with a higher shutter speed since both methods increase the amount of light hitting the image sensor.

Many modern lenses and cameras have built in stabilization in order to allow you to use slower shutter speed and compensate for camera shake. The other option is to put the camera on a tripod which should effectively eliminate all camera shake. Using a tripod, however, is not always convenient.

The other side effect of slower shutter speeds is that you won’t be able to freeze the action. For example, if someone is moving they will be a blur in the image because the shutter stayed open long enough for them to change position.

Here is a photo that my older daughter made using a very slow shutter speed. You can see that the image is not sharp at all.  This shutter speed for this photo was 1/8 of a second.  It can be very difficult to hand hold a camera and make sharp images at such a slow shutter speed.

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Nikon D60, 18-55mm VR @ 40mm f5.6 1/8 ISO 1600

In order to freeze motion or action in a photo, you will need to be in a place with enough light that will allow you to choose a higher shutter speed and still make a proper exposure. In normal daylight, this is usually not an issue. Once you get above about 1/250 of a second, you should be able to freeze most movement in a scene.

This shot below was from a kids’ soccer game that I shot. You can see that the player and the ball are completely sharp and the action is frozen.  This shot was taken with shutter speed of 1/1250 of a second.

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Canon 40D, EF 70-200mm f4L @ 70mm f4 1/1250 ISO 800

While shutter speed is part of determining the overall exposure of a photo, it is important to remember that as the shutter speed slows down in low light situations, you run the risk of blurry photos.  This can be a problem with many consumer grade camera since they typically don’t offer very wide aperture lenses and using the high ISO values can produce a lot of noise in the photos (see my post on noise reduction).  Using a flash can certainly help in low light, but if you prefer the look of natural light, you will need to practice a good technique for keeping the camera steady while hand holding it, or use a tripod.

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