How to get flash in sync
Slow Sync is useful when shooting in low light, allowing a long exposure to be combined with a brief burst of flash. Rear Curtain Sync allows you to fire the flash at the end of an exposure, rather than at the start.
Automatic camera modes default to a flash sync speed of 1/60 sec, which is too short to allow much ambient light in at night.
Slow Sync flash
By using slow-sync flash, a longer exposure can be used to allow ambient light to register on the sensor as well. Use a tripod too.
Front Curtain Sync
In a long exposure, subject movement recorded after the flash fires will appear as a trail in front – they’ll seem to be travelling backwards!
Rear Curtain Sync
The results look more natural, but it’s harder to predict where the subject will be when the flash fires at the end of the exposure.