Just got me a QL17 and I found something not mentioned in the manual is that ambient light level affect the aperture setting when using in GN flash mode. When I set a high shutter speed then basically the aperture only varies with focus distance and that's what I expected. What I didn't expect is that when using a slow shutter speed ambient light does make the aperture stop down a bit. Because of this it would be interesting to use the camera for daylight fill flash.