Thanks for the reply, my easiest, first option is to use the 25mm tube, but I am not able tell apriori, what kind of mag that would get me. I heard that to get a 1:1 reproduction ratio, you need a tube the same length as the focal length of your lens. But my 100mm macro is already 1:1, so I don't know how putting a tube will affect this ratio.
Thanks for mentioning about the number of flashes I need too. I think I'll try with 3 flashes to start with. I have several u/w strobes (flashes) that come integrated with the slave, adding flashes to the picture should not be problem.
I also have a 500D filter-type lens, but I tend to use that with my 300/4. From my understanding of the 500D, it allows you to focus at a distance of approximately 500mm. well, for this I want to be focusing at a much closer distance than that so I believe the 500D will not be useful for this. At this time, in my mind the options are using the 100/2.8 + tube, or 100/2.8 + reversed 50/1.4, or both. Does anyone know if I can reverse a lens onto the 300/4?
BTW, what is this 2x or 3x type macro lens you mention above? specialized macro lens that can shoot 1:2 or 1:3? Incidentally, I dont plan to be making any huge purchases for this experiment, just want to see if anyone has ideas or tried this before with non-specializezd equipment and had some degree of success?