Shutter Speed Light

• Shutter speed controls the ambient light when using flash
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• Controlling light from the flash
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• Controls that change the power settings on the flash
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• Flash is subject to distance

Aperture

Lower aperture is less light shown in flash
Lower fstop is a higher out put.

f11, f16, f22
f.4 f5.6

ISO

Changes flash and flash brightness (will also effect ambient light in scene).

Aperture 

Controls DOF and brightness of flash.

Pop up flash can cause red eye, it is short range and good to use as an emergency flash.
It is good for fill lighting to soften shadows

Flash mode ETTL.

Shutter speed controls ambient light.
Aperture controls flash output

F 3.5 = brighter flash
f22 = dimmer flash