Pentax K10D Operating Manual page 177

Using Trailing Curtain Sync
Trailing curtain sync discharges the flash immediately before the shutter
curtain closes. When shooting moving objects with a slow shutter speed,
Trailing curtain sync and Slow-speed sync produce different effects
depending on when the flash is discharged.
For example, when shooting a moving car with Trailing curtain sync,
trailing light is captured while the shutter is open and the flash captures the
car when the shutter is released. Therefore, a picture that looks as if light
is trailing is captured.
Slow-speed sync
1 Set the mode dial to any mode other than B or M.
2 Press the { button and press the four-way controller (3).
3 Select I and press the 4 button twice.
4 Press the K button.
5 Take the picture.
Trailing curtain sync slows the shutter speed. Turn off the Shake Reduction
function and use a tripod to avoid camera shake.
Trailing curtain sync
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