A visitor to our site contacted us yesterday with an interesting question about shutter speed. "Jim" is a newcomer to the DSLR world and is beginning to acquaint himself with manual exposure controls. His question is logical, but he's missing an important piece of the puzzle. Here is his question:
It makes sense, doesn't it? Jim is concerned about the overall clarity of his pictures (as any photographer should be) and he understands that there are two reasons why an image may not be clear. The first and most obvious reason is that the lens is not focused properly on the focal point. The second reason is that the shutter speed may be too slow to adequately freeze the motion of the subject and/or the camera itself.
Assuming that the camera lens has focused on the focal point (the most important part of the overall content that you want to see most clearly), motion is the only other thing that will affect clarity. If your subject moves - even slightly - a shutter speed that is slower than the subject's motion will result in a picture showing a blurred subject. And if the photographer moves the camera - again, even slightly - then everything in the frame will be blurry.
Our friend is correct in suggesting that the fastest shutter speed that's available on the camera will reduce the potential for motion blur. A shutter speed of 1/4000 of a second is fast enough to freeze most subject and camera movement. So his recommendation to always use the fastest shutter speed has merit.
But we also mentioned at the start of this post that a piece of the puzzle is missing. Consider that the faster the shutter speed, the shorter the exposure will be. 1/60th of a second (or a shutter speed of '60') is about the slowest recommended for everyday hand-held photography. Anything slower than that will almost certainly result in motion blur. 'Shutter speed' is, basically, the length of time the shutter is open, allowing light inside the camera
Now, stick with us here, because this is where it can get a bit confusing for newcomers to the DSLR. Try this. Count-off one second out loud. Next, imagine breaking-up that one second period of time into sixty equal segments. Imagine how little time just one of those segments lasts. This is the length of your exposure at a shutter speed of '60'. It's not a lot of time to allow light to enter the camera and make an exposure, is it?
That tiny segment of time gets even shorter as the shutter speed gets faster. So, at 1/4000 of a second, the sensor chip in Jim's camera is getting light for such a short period of time - a tiny fraction of a second - that there is far less light available to produce an image.
You see, when we talk about light in photographic exposure, it's a cumulative thing. Just like going to the beach on a sunny summer day. If you sit in the sun for fifteen minutes without sunscreen you'll likely see very little, if any, evidence of sun exposure on your skin. However, if you sit there for two hours, you'll definitely see the result on your skin and appreciate how light exposure can accumulate with time.
To wrap it up, Jim is right that the fastest shutter speed will help avoid motion blur, but it comes at a cost. And the cost is light. In order to use the fastest shutter speed, a photographer needs a combination of a tremendous amount of light, and/or a wide-open aperture (low number f/stop), and/or high sensitivity ISO. The reality is that you don't usually have a tremendous amount of light, wide-open apertures produce a soft focus (which you often do not want) and high ISO settings produce a lot of noise (which kind of cancels-out the clarity thing).
Our contributing photographers here at FreePhotoCourse.com often shoot with very fast shutter speeds, but usually in very specific circumstances with ample bright light when very fast moving subjects.
We hope this helps clear-up a question that a lot of our readers have posed to us over the years!
Perspective on Photography is FreePhotoCourse.com's official Blog. This is where you can find updates, stories, news, links to photo "finds" and more from FreePhotoCourse's contributing photographers and writers.