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Camera shutter

Camera shutter - Photographer David Hemmings tells us all about the camera shutter.

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Digital Cameras

Shutter and lensThe shutter is fundamental to most cameras including video equipment. It times how long the continuous light (not flash usually) is acting on the film or sensor and controls the exposure along with the aperture.

It also decides how moving subjects will appear in the picture e.g. blurred or sharp.

Polo match Waterfall long exposure
Fast shutter speed. Slow shutter speed.

The earliest shutter was hardly more than a piece of card or tape held over the ‘lens’ or pinhole which was removed for a set period. The time normally ran into seconds or minutes due to the low sensitivity of film and the small apertures used.

Shutters are normally between-the-lens (Leaf) or Focal Plane.

Leaf types can usually be found in older cameras, film compacts and medium format camera lenses. Focal plane shutters are generally used on SLR’s.

Focal plane shutter – vertically running, this gives more opportunity for higher speeds as there is less travel for the blades.
Leaf shutter Focal plane shuuter
Leaf shutter mechanism. Vertical shutter mechanism.

The main differences between the two is the range of speeds and the highest flash (sync) speed. Leaf shutters can sync over their complete range of  1/500sec to 4 or 8 sec. Focal planes can run from 30sec to 1/8000sec but have relatively low sync speeds typically 1/90sec to 1/250sec.

Vertical shutter mechanismWhat is synchronisation?
There has always been a need to make sure the light output from bulbs and flash are captured efficiently. Filament bulbs need time to reach max. power and are fired just before the shutter is opened. With flash there's no warm-up but the shutter needs to be fully open. Leaf shutters do this at all speeds but focal plane types form a narrow slit at their higher settings.
At slower speeds the shutter blades are fully open, thus allowing flash photography to be possible.  Most cameras prevent unsynchronised flash and shutter automatically.  High speed flash sync allows higher speeds by ‘burning’ the flash for longer but this greatly reduces power

This is a typical shutter and 1/250sec is too fast for flash so is therefore not ‘synchronised’.  You can see apart from the area within the narrow slit, the rest of the image will not appear as it is shielded by the shutter blades.  In daylight the flash would not be effective at this shutter speed and the image would appear to have been taken by continuous light alone.

Perntax 67 Mk11Minimising camera shake:
For hand holding the shutter speed should not fall below the reciprocal of the focal length in use. E.g., use 125th when a lens is zoomed to 100mm. Even with wide-angles it is advisable not to let the shutter fall below 125th as it may then be the subject that causes the movement rather than camera shake. 
One of the larger shutters to be found is on the discontinued  Pentax 67 medium format camera.  If not used with care and even with the mirror locked up, the shutter itself can cause camera shake.

Shutter speeds
Many cameras have 1/2 steps or 1/3 steps increments for their shutter speeds which can cause confusion. As an example 0’’7 is 3/4 second.

Seconds are shown as (’’) to distinguish them from thousands of a second or fractions of a seconds. For example: (4’’) is 4 seconds, (4) is 1/4sec and (350) is 1/350sec.

Exposure setting
When you set your choice of shutter speed the camera will automatically set the aperture for correct exposure. If the aperture value blinks in the viewfinder it indicates the camera is unable to find a suitable aperture for correct exposure. Usually it is because your choice of shutter speed is too high - set a slower speed until the display stops blinking. You cannot usually choose fast shutter speeds and expect small apertures i.e. F/22 unless there is bright light or the film is fast e.g. ISO800. 

Shutter priority is ideal for action and motion effects. Bracket with different shutter speeds when you are not certain of the optimum speed.  The table below will help give you a starting point.
Shutter speed guide

Final tip: 
Do not use a pressurised ‘air’ to clean the rear of the camera close to the shutter. The shutter blades are thin and delicate and may be distorted or overlap incorrectly if a blast of air should catch them. Earlier shutters were made of rubberised cloth and were a little more robust.  Use a hand blower instead - they are more gentle. 

Visit David Hemming's website.

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