S2 and studio flash
Forgot to say, a good way to test a camera and its ISO correctness (is that a real word?) is to shoot without flash outside on a nice clear sunny day near sea level at the "sunny 16 rule". Shoot at 1/ISO at F16. So, ISO 100 at 1/125 @F/16 (close to 1/100) and you should get a relatively good exposure. If sunlit subjects are 2 stops over/under exposed in these conditions, you have a lens or body problem!