Originally posted by arnold urely the mirror is supposed to move up first and then the shutter trip
I like calling it the Pentax flick... it is possible to do on many of the Pentax mechanical bodies that use the similar design. MX, KM, KX, K1000, Spotmatic I & II and pre-Spotties can do it too as long as it is a mechanical one with no automation to the shutter. The mechanism is a two part action rather than a sequential one or in other words...
...mirror up- release shutter, but instead for some pentax bodies...
...mirror up- release blocker- shutter may fire -full press, fire shutter.
If you poise your finger at the edge of the release button and flick the tip of your finger off the button, then the mirror will do that for all listed above.
On some that can't, it seems that the release rod is set too tight, but on all my bodies I seem to easily do this every time.
Hope that helped.