Without Slow Synchronization With Slow Synchronization Click on the image to see a larger one This problem can be overcome using slow synchronization . Slow synchronization means after sending out flash light, the shutter stays open for a little longer. In this way, the flash light illuminates main subjects and the slow shutter speed helps capture the background. The right image above shows the effect of slow synchronization. As you can see, the background pops up and the snow in the foreground looks more natural.
Slow synchronization can also make an image to look more natural.
The left image below uses flash without slow synchronization. It does not look like the actual scene which should be warmer. With slow synchronization, we have the right image. Now, the foreground is illuminated by the flash, and the background, which is illuminated by a table-top lamp, becomes warmer and looks more natural. Once SLOW appears, all subsequent shots using flash will use slow synchronization.