What is Shutter Speed?
Shutter speed is the amount of time that the shutter stays open.
The shutter is located in the camera just in front of the sensor and consists of two separate curtains – as the shutter release button is pressed one curtain opens to expose the sensor to light, followed by the second curtain closing to block the light.
Most shutter speeds are measured in fractions of a second – so a shutter speed of 60 means that the shutter remains open for 1/60th of a second. Thus the smaller the number the longer the shutter remains open – the slower the shutter speed.
The fastest shutter speed of the Olympus E520 is 1/4000th of a second.
4000 2000 1000 500 250 125 60 30 15 8 4 2 1
The shutter speed settings are in steps each of which halves or doubles the length of time the shutter remains open – or the exposure time of the sensor to light.
A change in shutter speed from 250 to 125 (or 1/250th second to 1/125th second) doubles the exposure time; whereas changing the shutter speed to 500 (1/250th second to 1/500th second) halves the exposure time.
Shutter speeds can be longer than 1 second; the annotation for these is that the speed is followed by a quote mark “. Thus a shutter speed of 2 seconds is displayed as 2”.
The Olympus E520 can have a shutter sped as slow as 60 seconds (60”).
There is also a shutter speed setting called ‘bulb’. In this mode the shutter release is pressed once to open the shutter and a second time to close the shutter. The amount of time the shutter remains open is determined by the operator. With this setting movement can be tracked e.g. stars in the sky, car lights on a road.
Shutter speed and motion.
Shutter speed has a direct effect upon the recording of motion within a photograph. An image in motion will be frozen at a fast shutter speed, whereas the same image taken at a slower speed will probably be blurred.
I plan to take photos within my garden of birds and animals whose movement is not only fast but also unpredictable – for this I will need to use a fast shutter speed. I also plan to take photos of plants and trees which might be quite still so a slower shutter speed can be used – but even leaves blowing in a gentle breeze can be blurred with a slow shutter speed.
Shutter speed and the hand held camera.
When holding a camera in your hands a very slow shutter speed will cause blurring of the whole image. If using a shutter speed of 4 (1/4 second) the shutter remains open for a relatively long time with the effect that camera shake will cause blurring. For this situation the use of a tripod to stabilise the camera and prevent camera shake is essential.
Shutter speed and focal length.
Focal length is the measurement in millimetres from the optical centre of the lens to the camera’s sensor.
If a camera is hand held (without use of flash) using a shutter speed slower than the reciprocal of the focal length will result in a blurred image.
Focal length | 1/focal length | Closest shutter speed |
28mm | 1/28 | 1/30th second |
50mm | 1/50 | 1/50th second |
100mm | 1/100 | 1/100th second |
300mm | 1/300 | 1/320th second |
The Olympus E520 contains an image stabilisation system. Image stabilisation will to a certain extent counteract the movement of the hand held camera. This means that shutter speeds slower than the reciprocal of the focal length can be used without blurring – but only for stationary objects.
The table above becomes:
Focal length | 1/focal length | Closest shutter speed |
28mm | 1/28 | 1/15th second |
50mm | 1/50 | 1/30th second |
100mm | 1/100 | 1/50th second |
300mm | 1/300 | 1/160th second |
References:
Collins Complete Photography Course. John Garrett and Graeme Harrris. 2008. Harper Collins Publishers. ISBN: 978-0-00-727992-0
Get the most from your digital SLR. The Digital SLR Guide. Chris Roberts. 2008. Downloaded from the Internet March 2009.
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