Long-term synchronization
The slow-sync is a photographic recording method of flash photography , in which the shutter speed is always longer than the flash sync speed is. The synchronization of the flashlight takes place here with the X-synchronization or the M-synchronization.
The technology
In flash photography, the flash is usually synchronized to the fastest shutter speed at which the shutter is fully open. Modern cameras allow shutter speeds that are longer than the flash sync time during flash exposure. By default, the flash is fired at the moment when the first shutter curtain is fully open, i.e. at the beginning of the exposure time with the shutter fully open. Many cameras also allow flash synchronization with the second shutter curtain. The flash is fired at the moment when the second shutter curtain is still open, i.e. at the end of the exposure time with the shutter fully open.
Applications
The camera usually selects fast shutter speeds when taking pictures with the flash. As a result, when there is little light and a great depth of space, for example when taking pictures outdoors at night, the foreground subject is shown brightly by the flash, while the background remains dark due to the short shutter speed and the short range of the flash. With long-time synchronization, the flash ensures that the foreground subject is well illuminated and the long exposure time ensures that the background is sufficiently bright.
Interesting effects can be achieved with motion sequences using long-term synchronization. By combining the flash light with a long exposure time, movements at the moment of flashing create a sharp, bright, frozen image of the movement and, during the rest of the exposure time, a blurred wipe effect corresponding to the movement . This gives the movement in the picture a strong dynamic impression. When the flash is synchronized with the first shutter curtain, the wiping effect precedes the frozen moment of movement, which counteracts the natural impression of movement. When the flash is synchronized with the second shutter curtain, the wiping effect lags behind the frozen moment of movement. This enhances the natural impression of movement. If the camera only supports synchronization on the first shutter curtain, it is possible to obtain the synchronization effect on the second shutter curtain by performing the movement against the desired image effect.