Displaying The Optical Preview - Pentax K-5 Operating Manual

I
Position the subject inside the AF
frame and press the shutter
release button halfway to focus
on the subject.
2
3
Turn the main switch to O while
looking through the viewfinder.
You can check the depth of field in the
viewfinder while the main switch is set to
the position 0.
During this time, no shooting information
is displayed in the viewfinder, and the
shutter cannot be released.
Take your finger off the main switch.
Optical Preview is ended and the camera is ready to take a picture.