Ricoh GF-1 - Manual (Page 15)

EN - 
SLAVE1: Mode for cameras with a pre-flash (triggered once)
and a main flash (Type R and other cameras)
SLAVE2: Mode for cameras with a main flash only
Following is the explanation for how to use the camera's
built-in flash as a trigger.
Type R cameras
If you are using the camera’s built-in flash as a trigger, do not
attach this flash unit to the hot shoe. The built-in flash may not
be able to open.
1 Turn on the power of the camera and the flash unit and set the
flash to always fire.
2 Set the flash mode to SLAVE1 with the Mode select button.
When set to slave mode, the flash unit’s AF auxiliary light
blinks.
3 Set the flash power level to Ambient light auto (F2.8 to 5.6) or
Manual flash (1/4 or FULL) with the Flash power level select
button.
Caution
The camera's Red-eye flash function is not available.
When using Ambient light auto
Set the aperture value.
1 Manually select the aperture on the camera to match the
aperture value selected on the flash unit. If the camera does
not offer the exact same value, select the closest value. When
using a zoom lens, check the aperture value again after
adjusting the zoom and correct the aperture value if necessary.
2 Use the supplied flash stand or other device to place the flash
unit at the desired location and adjust its angle as desired.
3 Press the camera's shutter release button once to check that
the flash fires under the conditions selected.
If the flash does not fire, verify the position of the slave sensor
and the operating distance.
If after checking the results of a test shot the image is too dark,
select a smaller aperture value on the camera. If it is too bright,
select a larger aperture value instead.