[Rainer]

From your description, there are only few reasons left ...



- you''ve set camera and meter to the same iso-setting.

- you're at 1/160sec ... well within X-sync-time

- The camera is in M mode, ynd you set the aperture from

the meter reading.



so either

- the meter does not see the flash ... and therefore gives you a

reading for the ambient light

or

- the meter is not set for flashmetering and averages the light

over longer times ... and again gives you a reading for the ambient light



In both cases, since ambient light is magnitudes darker than the flash, the

resulting picture will be overexposed. ... by 8 stops ... well that is much, but

since it depends on the level of ambient light you have, it is possible.



But lets do the reverse calculation ... the 580ex has a GN of 58 (max) at 100iso.

This is approx. 80 at 200iso. Using a distance flash to subject of say 3 meters

you would have to use f/27 ... the flash was set to 1/4 and it goes through

the umbrella ... this costs about 3 stops ... this would bring you down to f/8



So ... around f/8 should give you a well exposed image ... using f/1.4 is

5 stops overexposed ... the 8 stops you mention are at least possible

(different distance ... umbrealla that doesn't eat up one stop).