Originally posted by saladin 
sorry to post yet again. i'm learning as i go, and hopefully some of this will make sense to someone, or even be of some help. the shutter speed when the flash is up seems to be constant irrespective of the aperture size - i can stop right down to f38 and the shutter doesn't change!. but the speed does get quicker as i wind the zoom out from 55mm to 18 mm (it comes down to 1/30 sec at 18mm). so i'd say the flash works by looking at the focal length of the lens, and then the objects distance ( guess that makes sense), then adjusts the intensity/timing of the burst to obtain what it thinks is correct exposure. to check this, i dialled in 1 stop of over exposure compensation. the shutter speed remained at 1/60 - as it appears it always will with the lens at 55mm - but the exposure definitely advanced to about right. so the flash is adjusting is output. it must obviously be applying relatively more light when the aperture is smaller than when it is larger - hence the brighter pictures at larger f-numbers.
now i am a novice really, so someone may be able to explain exactly why this is, and what i should do to shoot around it. i have not looked into flash compensation yet - not sure what that is actually doing - but could this be the answer?
That's by design. The camera can only sync to a certain max speed when using the flash. the issue is that the shutter needs to be fully open when the flsh fires, or you'll get a properly exposed zone and an underexposed zone where the shutter is blocking the light if the shutter speed is faster than the sync speed.
Similar Threads 
