spk1965 wrote:Thanks Lester

Makes alot of sense. So with the Canon 100mm/f2.8 how far can I stop down? I'm I best off in Manual, Av, or Tv mode? I assume that I don't worry too much about achieving correct EV values as the flash fill will take care of foreground and background. Is this right or totally ignorant?
Thanks.
If using flash with the 100mm I tend to use manual 100 ISO, set the shutter sync speed and use f16. Sharper results but with less DOF might be obtained using f11. As a variation you can get some background exposure by increasing the ambient light exposure, perhaps ISO 200, 1/200, f11. With the MP-E I tend to use f8-f16 depending on the magnification.
Using ambient light with the 100mm possibly ISO 400 or 800, down as far as 1/160 but possibly 1/250 if possible and f8 or f11 depending on subject and light. I also use a monopod if at all possible.
In fact I use a monopod even with flash, paricularly with the MP-E at higher magnifications, as this not only steadies the focus but helps take the weight of the kit of my old bones. 