It's my understanding that shutter speed controls the ambient light and aperture controls the amount of light from the flash. Is that right, Gerry?
Errr it's GARRY
While Garry makes a SHOUTING point about shutter speeds being irrelevant, some here seem to have not entirely understood that point - so calmly - I'll try to elaborate
Any flash exposure has 2 parts - 1 is the exposure for any ambient light, and 2 - is for the exposure with the flash
Where 1 is so low as to record nothing at all - i.e. pressing the shutter to fire at 1 second, 1/8th second, 1/60th second, 1/125th second, or whatever your flash sync speed it means you only get black - so nothing records - then clearly the speed of the shutter is making no difference - there is not light about, so all is black
2 is the flash exposure
Here a burst of light is emitted to light your subject when otherwise nothing would be recorded as in 1 above
The power of the flash then records as over/correct/under exposed due entirely to it's power v the aperture. The actual flash may last only 1/500th second or up to 1/30,000th sec
During such a shot - all your shutter speed is doing is allowing the shutter to open... then a flash goes off... then the shutter closes
Imagine in a dark room your shutter speed is 1 second
You shoot it, and nothing at all records
Now you fire a flash when the shutter opens... if the flash is bright enough to correctly expose a shot at f8, you have a shot in the bag
Depending on how powerful that flashgun/studio light was - the burst of light emitted to achieve a correct exposure of f8 may have been 1/500th sec or even 1/30,000th sec. If it was massively powerful it could have been 1/million th of a second (where you see shots of bullets stopped dead as they enter a balloon for example)
Your camera's shutter was open for the same length of time - but records nothing at all - the flash is powered to record an image at f8 - so whatever speed the flash lasts is the effective exposure time. Hence you can have a 1 second exposure of your shutter, but the flash can stop dead a bunch of cheerleaders, or if powerful enough, a bullet too
So changing your shutter speed from 1/125th to 1/180 makes no differnce at all
Get it now?
HTH
DD