I always hear, "shutter speed controls ambient exposure, aperture controls flash exposure." However, isn't it really "...aperture controls flash and ambient exposure"?
Without the flash, exposure is controlled by shutter speed, ISO, and aperture. Doesn't the aperture still effect ambient light even when using a flash?
Let's say I want to under expose the background (ambient light) by two stops. I do a meter reading and it says 1/60 f/4 at ISO 100. I can now underexpose the background by two stops while using flash in 1 of 2 ways:
1). Setup a flash so I get a meter reading of 1/60 f/8 at ISO 100. I then set my camera to these settings, and fire away. Haven't I accomplished my goal of under exposing ambient light by two stops even though I only adjusted the aperture?
2). Setup a flash so I get a meter reading of 1/60 f/4 ISO 100. I then adjust the shutter speed to 1/200 and fire away.
Of the two, I think #2 is better because the flash doesn't have to work as hard, but both are valid options, right? What would be the difference between the two images? Would#2 have less shadows?