Pentax K-7 Operating Manual page 114

The shutter speed is locked at 1/180 seconds. Use this when using an
external flash that does not automatically set the sync speed.
I Set the mode dial to X.
' Turn the rear e_dial (%_,,_) to adjust the aperture Valuel
, Press the ® (Green) button to retain the shutter speed at 1/180 seconds and
automatically adjust the aperturel
• When the sensitivity is set to [AUTO] and the exposure mode is set to X
mode, the sensitivity is the lowest sensitivity set in '!Setting the Range of
Automatic Correction in AUTO" (p.90).