Modern Digital Single Lens Reflex (DSLR) cameras have mechanical components for both the shutter and the mirror mechanism. These mechanical components can have a significent effect on the sharpness of any image due to the vibrations within the camera causing the camera to move. The mirror slap vibrations in particular will cause a degradation in the image sharpness which may be increased by using lenses of a longer focal length. A longer lens will effectively magnify the camera movement and shorter focal length lenses wioll have less effect on the loss of sharpness.
Lens Focal Length
The effect of the loss of sharpness can be measured by photographing a resolution chart to determine the sharpness at various shutter speeds. In general any loss of sharpness effect is not noticable when lense of 50mm or shorter are used. However with lenses longer than 50mm, some image degradion will commence. At a focal length of 100mm the mirror slap degradation will commence and get worse as the focal length is increased.
High shutter speeds can be used to help reduce the effect of mirror slap. In general a shutter speed of 1/250 second or greater will reduce the effect of the image degradation. Also with shorter speeds when taking long exposures, the exposures should be kept longer than 2 seconds to reduce this effect.
Methods to eliminate Camera Vibrations
There are several methods that a photographer can use to help reduce the effect of mirror slap.
- Some cameras have a facility to lock up the mirror prior to the actual exposure and this will help to ensure that the vibrations cease before the exposure takes place. A delay of several seconds is required for the best effect. This is the most effective way of reducing the effect of mirror slap.
- It is generally thought that a tripod will help reduce the effect of mirror slap however this is not always the case. The main reason for using a tripod is to avoid camera movenment due to physically moving the camera and not holding it steady.
If using a lens longer than 50mm, try to use a shutter speed of 1/250 second or greater and your images will be significantly sharper. Also use the mirror lock up where ever possible.
I am also a firm believer that the more weight that there is in the tripod and the ball head then the more that the camera will be stabilised against any vibration or movement.