In case you, like many photographers, wonder how aperture and shutter, as well as ISO and flash power, affect your flash pictures – here’s how!
Study that graph – a good photographer knows this graph off by heart – in fact, a good photographer has made this chart part of his or her DNA.
Note that if you set your camera to an automatic mode (like P), or if you set your flash to an automatic mode (i.e. TTL), you’ll get confused, since the camera varies things! So when learning, keep everything on manual.