Pentax K-X Operating Manual page 49

1 Set the mode dial to P, Sv, Tv, Av or M.
2 Press the four-way controller (T).
The [Flash Mode]screen appears.
3 Select _ or >_ and press the
OK
button.
Press the _UP/_ button.
The built-in flash pops up.
5 Take a picture.
Trailing Curtain SYnc slows the shutter speed. Use the Shake Reduction
function or turn off the Shake Reduction function and use a tripod to avoid
Camera shake.