workshop session 4 – shutter speed and motion
This is the fourth session in the Introduction to Digital Photography; the workshop met February 24.
The topics for session four are:
- shutter speed,
- exposure compensation, and
Like aperture, shutter speed has two aspects to come to terms with:
- shutter speed as a component of exposure, and
- shutter speed as a creative element.
Where aperture is a measure of the diameter of the iris, shutter speed is a measure of the duration that the iris is open.
In Session three we discussed exposure or Ev with a focus on aperture ƒ-stop. In this session we focus on shutter speed.
Shutter Speed and Exposure
Exposure is a measure of the amount of light recorded by the sensor. For our purposes exposure value, often written as Ev or EV, can be defined as a function dependent on aperture size N measured in ƒ-stops and shutter speed, or exposure time t measured in seconds.
By ignoring the ‘log2’ part we can treat this as a simple reciprocal function – and reciprocal functions act like see-saws. To end up with the same exposure value or Ev, when one part goes up the other must come down.
So if we need to keep the same exposure value, changing shutter speed means we must change aperture ƒ-stop. If we keep the shutter open longer, we must reduce the aperture. Likewise if we close the shutter sooner, we must increase the aperture.
Unlike aperture ƒ-stop which is a ratio, shutter speed is an absolute number, expressed in seconds, either whole or as a fraction.
Speeds at or slower than one third of a second as usually shown as a number with a decimal point (ie 0.3 or 1.5) often followed with a quote mark ("), the symbol for seconds. Usually anything faster than one third of a second is shown either as a fraction (ie 1/60) or as a whole number (in this case 60).
Shutter speed typically ranges from 30" to 1/4000". Along this continuum there are some special points with unique considerations ...
- at 1/2000” most action or motion will be frozen,
- 1/250” will freeze modern day motion – people walking, etc.; this is also the fastest speed for panning, and
- 1/60” is the longest time for handheld; any slower you’ll need to brace the camera on something solid or use a tripod; remember that if you use a tripod, turn off image stabilization or shake reduction.
Shutter Speed as a Creative Element
This animation shows various shutter speeds and their effect on flowing water. At 1" the flowing motion of the water is captured. As the shutter speed is shortened, more and more of the water flow becomes frozen until individual water droplets can be seen (at 1/800").
At the other extreme, keeping the shutter open for more than a second allows us to create some spectacular images. Here a shutter speed of 30" blurs the head and tail lights of cars on the M3 in the UK.
By combining shutter speed and panning we can show movement along a straight line. Your camera must be set at a relatively slow shutter speed – somewhere between 1/60" and 1/250". Choose a subject a that is moving in a straight, predictable, motion. Follow the subject smoothly with your camera and when you are moving at the same rate as the subject, press the shutter release button, and continue moving. This technique takes some practice but the results can be dramatic.
That pretty much wraps up shutter speed. Although a relatively simple part of Ev, the creative aspects are great fun to explore and can produce some spectacular results!
After introducing exposure compensation and histograms, this sessions assignment extends on shutter speed and motion ... assignment 4