When and how do you use fill in and slow sync in photography?

Question

When and how do you use fill in and slow sync in photography?

Answer 1

Fill is used to soften an uneven lit subject, for example when a subject is lit from only one direction - fill is used to break up the shadows.  Slow sync is used to allow ambient light to fill the background as its exposure tends to be much slower than the subject when using flash.  When using flash and not in slow sync mode, many cameras default the shutter speed to 1/60 and range up to the maximum sync speed for that camera.  Slow sync allows for a slower shutter speed.  For example, if the exposure of ambient light in the background of your shot is 1/15 and your default shutter speed for flash is 1/60, the background will be very dark.  If you are able to set the shutter speed at 1/15, you can allow the ambient light to fill in the background as the subject's exposure is set and frozen by the flash.  It just makes shots using flash look more natural.

Answer 2

Fill flash adds enough light to "fill" some shadow areas but not to delete all shadows or to significantly change the overall lighting. It tends to give you a softer but flatter look. Slow sync is used in dark areas where you want to shoot at slow shutter speeds to keep backgroung lighting but have the flash fire to give you a sharp picture of the subject in the foreground.  

Answer 3

Fill flash is used in low light conditions to light the scene.  Your on board flash will get out about 4 ft.  An external flash that can be mounted to a flash bracket(like a wedding photographer uses) or on the cameras hot shoe significantly increases that distance.  The fill flash lighting is a flat but flattering type of lighting as it does not show wrinkles on the face.  It is also used in bright sunny conditions to prevent harsh shadows and the raccoon eye effect.