Nikon D300 - Manual (Page 316)

290
U
e2: Flash Shutter Speed
This option determines the slowest shutter speed available when
using front- or rear-curtain sync or red-eye reduction in
programmed auto or aperture-priority auto exposure modes
(regardless of the setting chosen, shutter speeds can be as slow as
30 s in shutter-priority auto and manual exposure modes or at
flash settings of slow sync, slow rear-curtain sync, or red-eye
reduction with slow sync). Options range from
1 /
60
s ([1/60 s], the
default setting) to 30 s ([30 s]).