This is part two of our four part series, Understanding Exposure. This series of articles will explain everything a photographer needs to know about how the light gets into their camera and how their camera uses light to record the scene.
In Part 1 we discussed ISO — how it works and why you would choose a particular value of ISO.
In this, Part 2, we’ll be discussing Shutter Speed. In my opinion, Shutter Speed is the easiest of the exposure triumvirate to understand — the triumvirate being ISO, shutter speed and aperture.
In most modern cameras the shutter is a curtain that moves vertically down to open and allow light that’s coming through the lens to pass to the image sensor. When the exposure is done, it closes from the top.
Common shutter speeds in most modern DSLR’s range from 1/4000th of a second to 30 seconds. Today’s DSLR’s also have a bulb function which means that the shutter opens and stays open as long as the photographer presses down on the shutter button. When the photographer releases the button, the shutter will close. Shutter speeds of several minutes to hours can be achieved using the bulb function.
A shutter speed is considered slow at speeds that are an inverse of the lens focal length. For example, if you’re shooting with a 70-200mm lens at 200mm, you should guard against your shutter speed being slower than 1/200th of a second without the use of a tripod. If your lens or camera has some form of optical image stabilization, you may be able to use shutter speeds slower than the inverse of the focal length but even if that is the case, it usually is best practice to avoid shutter speeds slower than the inverse of the focal length.
Pop Quiz
You’re shooting with a 28-300mm lens at 60mm. Neither the lens or the camera have optical image stabilization and you don’t have a tripod. What is the slowest shutter speed you should use? (Answer is at the end of the article)
Remember from Part 1 that as ISO increases, noise i.e. grain increases. With a slow shutter speed, one can keep ISO low and the resultant image relatively noise free. Of course at slower shutter speeds you have to be concerned about camera shake so a tripod may be needed in many situations.
A photographer also my want a slow shutter speed to create some creative blur in their image.
Conversely, when the photographer wants to freeze action, they’ll choose a fast shutter speed. Action sports such as football and hockey dictate shutter speeds faster than 1/1000th of a second. With speeds that fast, motion is frozen with the image being crisp and blur free.
Finally, sometimes a photographer would like a shutter speed in the middle range — the middle range being defined by the focal length of the lens being used but very generally, mid-level shutter speeds are usually slower than 1/1000th of a second but faster than 1/60th of a second. A photographer will utilize these shutter speeds when they wish to convey some motion yet keep the subject relative crisp and clear.
Shutter Priority – Most modern DSLR’s have a setting called Shutter Priority. All this means is that the photographer will set the shutter speed and let the camera choose the aperture to achieve proper exposure. If you remember from Part 1, if the photographer has Auto ISO set, the camera will also pick the ISO needed to expose the shot.
You would use Shutter Priority when you either want to freeze the action or blur the action. As I mentioned, action sport photographers want fast shutter speeds so they’ll often have their camera in Shutter Priority mode and dial in a very fast shutter speed. They’ll than adjust the ISO so that the camera’s computer utilizes an aperture that is in the photographer’s acceptable range.
Of course if the photographer wants to induce some creative blur into their capture, they’ll use a slow shutter speed.
That is all you really need to know about shutter speed. Remember, if blur or lack of blur is most important to you, put your camera in Shutter Priority mode and pick the shutter speed that will give you the result you seek.
In Part 3 of Understanding Exposure we’ll be discussing Aperture — in my opinion, the most difficult of the exposure triumvirate — but still pretty easy!
Answer to the Pop Quiz
If you answered, 1/60th of a second, reward yourself with a treat because you are correct!
