Messing around with various macro lens combinations - seeing what lens could be reversed in front of what, which lenses worked well with the 500D diopter, and how any of them compared with using a dedicated macro lens.

Very unscientific tests but I did discover that reversing the 35 F/4L in front of the 400 F/5.6L gives a wicked magnification (and it fits quite nicely inside the lens hood.....

Anyway, this one was with the 500D diopter mounted in the 70-200 F/2.8L, which is a reasonably hand-holdable solution for moderate magnification.