Nikon D300 User Manual page 758

External Speedlight flash units offer modes like TTL BL,
TTL BL FP, TTL FP, or just TTL. TTL stand for
through-the-lens, and represents an i-TTL mode (intelligent
though-the-lens). BL stands for balanced. FP stands for Auto
FP high-speed sync mode. Refer to your flash unit's user's
manual for exact details on how to switch between modes on
the flash unit.
When I'm shooting outside (only) and want a great exposure
of my subject's surroundings, along with the subject, I'll
often use Slow sync mode. The only caveat to this is that you
must be aware that slow shutter speeds will cause ghosting
and blurring as the light falls.
I don't use the Red-eye reduction modes often because it
seems to confuse people. They think the initial shine of the
AF-assist illuminator is the flash firing and then look away
just as the main flash fires. If you are going to use Red-eye
reduction modes, you might want to tell your subject to wait
for the main flash.
Rear-curtain sync creates a cool effect if you want to show a
ghosted image stretching out behind your subject when you
use slow shutter speeds. Rear-curtain sync is sometimes used
by sports shooters in situations where there may be some
blurring from fast movement in low light. It is much more
acceptable to have a ghosted blur after the subject since it
implies motion. Front-curtain sync makes the blur show up in
front of the subject, which just plain looks weird.
I suggest experimenting with all five of these modes. You'll
need to use each of them at various times.
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