Shutter speed: in depth

The shutter on a camera is a sophisticated piece of electronics that precisely controls the amount of time the sensor is exposed to light.  The duration for which the shutter remains open is called 'shutter speed'. In photography speak, shutter speeds are said to be fast (shorter duration) and slow (longer duration). A shutter speed of 1/200 seconds is faster than a shutter speed of 1/60 seconds  (remember fractions :)).

"Clicking" activates the electronics that controls the shutter. As soon as the shutter is open, ambient light starts accumulating on the photographic medium (film or digital sensor) and continues to do so until the shutter closes again.  This means that by controlling the shutter speed we can make a bright, sunny day look grey and cloudy  (using a very fast shutter speed) or make a pitch-black night feel like dusk
or even midday (using a very slow shutter speed).  The sequence of images below were shot in quick succession in late afternoon light and illustrates the range of exposures that are possible by controlling the shutter speed alone.






Ok, so now we know what that shutter is, but how does this affect our photographs.  Great question :)
There are several factors that contribute to picking a shutter speed, chief among them, the ability to hold the camera steadily and, of course, your creative intent.

Hand-holdability

This is a limitation that arises due to human physiology (hands tremor, at least mine do) and the resolving power of the lenses used for photography. There is an upper bound to the shutter speed you can use to make hand-held photographs before they start getting blurred.  This upper limit is determined by the size of the sensor, the focal length used and of course, the photographer's own ability to keep still.  Since this is an introductory post I'll distill all these factors into a simple rule of thumb.

The rule of thumb is to set your shutter speed to the reciprocal of the focal length you intend to use.  The shutter speed you end up with is the slowest shutter speed you can use before images start to get blurred. So, if you're shooting with your lens' focal length at 50mm, use a shutter speed of 1/50s, at 80mm 1/80s at 320mm 1/320s. You get the idea.  The rule above applies to a 35mm sensor.

Most entry and mid-level DSLRs tend to use sensors that are smaller by a fixed ratio called the 'crop factor'.  For such cameras, the crop factor should be factored when choosing the shutter speed.

shutter speed = 1 / (focal length)

shutter speed = 1 / (focal length x crop factor)

Remember, that the rules above will help you get to a baseline number.  The limits will vary depending on the individual.  There is a lot of gory math this works.  Check here if you are interested in punishing yourself. place to get nerded out.

Shutter as a Creative Tool

The shutter is a fantastic tool that can be used to add creative touches to your images.  It can be used to blur and convey a sense of motion, to freeze high-speed action, and to create those smooth silken water streaks we see in images of waterfalls.

Blur Motion

By understanding the relative speeds of the various objects in your image you can intentionally blur parts of your image.  With the right kind of subject and composition this can result in very creative images.




The yellow blur in the background in the image above is a fast-moving train.  By using a relatively slow shutter I was able to render the train as a blur and keep the subject sharp.

Freezing Action

By stretching and contracting time, photography allows us to explore and understand our world in different time scales.  Modern cameras are capable of capturing unimaginably tiny slivers of time.  Even entry-level DSLRs can support shutter speeds down to 1/8000s (phew!).  This allows us a view of the world that we might otherwise never get to see.

Here's one example of high-speed photography that turns a mundane subject into a work of art.