[robski]

I think your find a true macro lens is tuned to give a flatter field of focus. If the lens was square onto a sheet of paper with text. The whole frame should be in focus at the same time. Standard lens tend to suffer some curvature in the field of focus. When the centre of the frame is in focus the edge of frame maybe out of focus. Then when you adjust to get the edge in focus the centre goes out of focus. With such shallow DOF at 1:1 this maybe important dependant on the subject matter.

I have just looked at spec sheet for my 100mm f2.8 macro. It says that f2.8 is when the lens is focused to infinity and you lose 2 stops of light when at 1:1 magnification.

I should think tubes and bellows are idea for studio setup but to lose infinity focusing for a walk about lens would be a pain. One minute you could be taking a closeup shot of an insect the next subject could be 30 feet away.

I went for a macro lens as the best closeup I could get with my other lens was 1:4. I doubt I will do much 1:1 work but it will handy for 1:2 or 1:3 without any fiddling around.