This is a brief article I wrote in response to a query made on a neowin forum.

To start off, the shutter is like a solid window blind, it allows light into the room when up/open and blocks all light when it’s down/closed. It’s primary purpose is to expose the film of the camera or the digital sensor of digital cameras to the light which has been carefully focused upon the film/sensor through the lens.

Without over complicating things, pretend we’re on an automatic setting on a digital camera – Auto mode (drunken night mode). The camera controls a varied range of things which will result in a generally accepted photograph – good balanced photo with reasonable exposure… your typical point and shoot produces decent photos in auto mode (generally, but this is a WHOLE other discussion..!).

If the camera is in auto mode, it will calculate the ISO (sensitivity of the sensor, it varies from photo to photo depending on light conditions), the shutter speed and the aperture of the lens. What is the aperture? That’s the small opening that lets light through, it can be set manually or controlled automatically depending on the results desired – different topic also. The shutter speed, aperture and ISO are all carefully balanced to produce a resulting photograph of (hopefully) acceptable exposure.

Shutter speeds can vary between anything like 1/8000th of a second to 30 seconds – it basically means how long the light has been allowed to reach the digital sensor inside the camera so it can view the light which is being focused through the lens. If you were to ignore the ISO and the aperture and focus on the shutter speed, this is what you can achieve with various shutter speeds.

With a fast shutter speed under excellent lighting conditions (very sunny day) with a shutter speed of 1/1000th of a second, you can take a photo of someone running and they will appear nicely lit with little or no motion blur (depending on how fast the person was running and how the photo was composed).

With a fast shutter speed under poor lighting conditions (late evening to nighttime) with a shutter speed of 1/1000th of a second you are almost guaranteed to have a really dark photograph, practically completely black and totally under exposed as a result (no image).

With a medium shutter speed under reasonable lighting conditions with a shutter speed of 1/100th of a second you can take a photo of someone running and achieve some sort of blur to give a better appearance of motion and action in the photograph.

With a slow shutter speed under reasonable lighting conditions with a shutter speed of 1/4 of a second you can take a photo of moving water in a river or waterfall in shadowy conditions to make a beautifully smoothed picture of water moving while the remainder of the photo is crisp clear (provided you use a tripod to avoid camera shake).

With a really slow shutter speed under really poor lighting conditions (night time by the sea) with a shutter speed of approx 20 seconds you can take a photo of the moon and the reflection on the water with good clarity (definitely need a tripod for this one!).

Sports photography generally uses fast shutter speeds where as night photography will most certainly require slower shutter speeds (to allow more light into the sensor).

You can achieve some amazing effects from long exposure photography – trailing car lights (streaking across the photo), flash photography with long exposure is also very possible with some very stunning effects.

Remember this one important thing – the slower the shutter speed, the more of a need for a tripod to avoid total blurring of the photograph. It’s acceptable for some objects or features of a photograph to be blurred due to their motion, but you must always avoid your own motion caused by natural body movement (nobody has surgically stable hands when standing or kneeling or otherwise, honestly!).

Some useful features like image stabilisation will reduce apparent camera shake caused by the camera used at long focal lengths or slow shutter speeds, but it’s not the savour in all situations.

Hope some of that info helps! Feel free to ask some more questions!

Link to the original thread on Neowin