Roger, I've shot at up to 30:1, albeit not with a long lens. Getting the illumination isn't much of a problem. Small flashes close to the subject will do the job perfectly well without frying anything. If you don't believe me, do the guide number arithmetic.

The real problems with high magnification photography are getting focus, maintaining focus, and stability. Getting focus is possible, maintaining focus and getting stability require a combination of brute force and subtlety. The first stand I built for photomacrography wasn't rigid enough, lost focus if I leaned on it while focusing and then let go.

If you don't have the two books I suggested earlier in this discussion, do yourself a favor and get them and read them. Or buy a copy of Brian Bracegirdle's Scientific Photomacrography, which is in one of the RMS' series.

You're absolutely right that the technique of shooting at high magnification is exacting.

That " even the specialist macro lenses are reaching the edges of their comfort zones" at 10x is simply wrong. It depends on the lens and the range of magnifications it is optimized for. I tried my little fixed aperture 25/2.8 Summar from 5:1 to 15:1; resolution increases with magification. Since the lens was made for a projection microscope, this makes sense. The 10/1.7 Mikrotar is best between 15:1 and 20:1, the 17/4 Tominon at 20:1

Cheers,

Dan

Oh, yes, you're absolutely right that the technique of shooting at high magnification is exacting.