Standard (X-)Flash Synchronization
Technology - Technology
In std. flash sync. mode the flash fires as soon as the whole film frame is fully exposed to the incoming light (see picture below). This time period is obviously limited towards higher shutter speeds dependent on the speed of the shutter/curtain mechanism. This max. flash sync. speed is given in the specification of a camera. The current fastest max. sync. speed is 1/500sec is close to the flash duration of strong flashlights (around ~1/500sec for a full burst). Consumer grade SLRs can normally sync. up to 1/180sec.

Despite the short flash duration the chosen flash sync. speed has certain effects on the final image. The main (flash) subject itself is quite independent from the chosen flash sync. speed because it is exposed with the speed of the flash duration. However, this is not true for the surrounding scene. There're a couple of possible side effects.
So the faster the flash sync. speed ...

  • ...the darker is the scene around your main subject because the ambient light has less influence on the exposure process. The effect is obviously dependent on the level of the ambient light.
  • ... with a moving scene (or a static scene with moving objects) the less blurred are the objects which are not (significantly) exposed by the flash light. etc.

Many cameras offer the possibility to synchronize either on the 1st or 2nd curtain. With 1st curtain sync. the flash is fired as soon as the 1st curtain is in upward position while with 2nd curtain sync. the flash is fired just before the 2nd curtain moves upwards. Obviously this means that the natural (ambient) light of a scene exposes the films either behind or before the flash burst. If you shoot e.g. a fast moving object with 2nd curtain sync. you'll get a blurred moving effect which will end in the (flash-) exposed object. With 1st curtain sync. it'll be the other way round.

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