Ricoh GF-1 - Manual (Page 12)

EN - 
Reference
About the illumination coverage
With Type R cameras, the illumination coverage will vary from 24 mm
to 105 mm, depending on the focal length.
You can use a illumination coverage of 105 mm to cover also focal
lengths beyond 105 mm toward the telephoto end. However,
when using focal lengths under 24 mm toward the wide angle
end, please use the wide panel (18 mm). In such case, the
illumination coverage will not be automatically linked to the
zoom position.
* All illumination coverage values given are 35-mm camera
equivalents.
About the focal length
If the image appears too dark even when using flash, get closer to
the subject or select a higher ISO setting on the camera.
To Better Enjoy Flash Photography
Ambient light auto flash
1 Set the flash mode to NORMAL with the Mode select button
and the flash power level to F2.8 - 5.6 with the Flash power
level select button. If the subject is relatively far or if you want
a short interval between flashes, select a power level of F2.8.
To get a deeper depth of field, select a power level of F5.6.
2 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.
3 Set a shutter speed slower than 1/250 second.
* For details on the camera's settings, see the Camera User
Guide.
* Depending on the shooting conditions (subject, surroundings,
color and reflectiveness of the background, etc.) the resulting
image may not come out as you expected. In such case, try
changing the aperture value on the camera or the shooting
distance.