Shake occurs when the camera is moved while recording. The rays of light that the lens focuses on the film plane or the sensor therefore travel during the recording and leave behind overlapping traces instead of clearly defined points. This effect occurs with every hand-held picture, but it is only perceived as blurring when there is a certain degree of blurring. A shortening of the exposure time counteracts the blurring, since the bundled light covers a shorter distance on the film or the sensor with the same movement of the camera and the picture becomes sharper. The greater the focal length of the lens or the larger the image scale , the greater the risk of blurring. In practice, a blurred photo usually affects the entire image area evenly, unless there is a rotational movement around the optical axis, which means that parts of the image can be blurred to different degrees.
On the other hand, we speak of motion blur when the object moves relative to the camera during the recording. While blurring is an undesirable effect, motion blur is used, for example, by dragging the camera along with the design. A moving object is shown in focus in this way, the background appears blurred.
As a rule of thumb for hand-held photos with 35mm format, the following applies to films: the exposure time should at most roughly correspond to the reciprocal of the focal length. This time is also known as the free hand limit. Modern high-resolution digital cameras achieve significantly higher image resolutions than medium-sensitive 35mm films, which are based on this rule of thumb. Therefore, the value for the camera shake limit must be shortened accordingly.
Examples of the rule of thumb for 35mm format (film):
- With a lens with a focal length of 50 mm, you can take photos by hand with a maximum exposure time of 1/50 second. 1/50 s cannot be set with many cameras, so the next shorter time of 1/60 s is the upper limit.
- A lens with a focal length of 250 mm requires an exposure time of 1/250 second or less in order to be able to take photos safely by hand.
To avoid blurring, hold the camera firmly with both hands and press it against your forehead. With a longer exposure time it is advisable to expose the body e.g. B. to lean against a wall. If the exposure time is well above the rule of thumb, the camera must be placed on a tripod or at least on a solid surface. A heavy lens is often placed on a bean bag .
Due to their low mass , the risk of camera shake is greater with compact cameras than with heavier built models such as SLR cameras . The photography technique used in many compact digital cameras to aim at the subject with arms held up because of the lack of a see-through also has an unfavorable effect .
In addition, it makes sense to use the self-timer or a remote shutter release for a long exposure time , since pressing the shutter release can cause blurring. For this purpose, some models have the option of setting the self-timer to two instead of the usual ten seconds.
With large focal lengths and an exposure time of longer than 1/10 of a second, the movement of the mirror of a single-lens reflex camera can cause the camera to jolt despite the tripod, and the image becomes blurred. You can counteract this with the help of mirror lock-up .
Some manufacturers offer image stabilization systems that counteract blurring and thus allow an exposure time that is up to four times longer. If the camera is immovably fixed, e.g. B. on a tripod, however, image stabilizers should be switched off. Otherwise you can lead to a blurred picture through your own initiative.
- Shake blur in the context of sensor size and focal length. digitalkamera.de, accessed on October 25, 2015 .
- Avoid shaky and blurry images. digitipps.ch, accessed on July 25, 2017 .