Barry:
I am somehow astonished about your (good) experiences with ring flashes, too.
Unfortunately, I can't recall the name of the ring flash I used.
I borrowed it from a friend of me a couple of years ago. But I remember that
it was quite heavy and that it could not be attached properly to the
objective (lens?) of my camera (Tokina/Minolta).
I also remember and that is the reason why assume it was the flash and nothing
else that the leaves of my sundews and especially the leaves of some utrics
(which however did not die later on) became totally soft in structure and wet.
I took the pictures in the greenhouse so that could not be the problem. The
distance might have a little bit shorter then 25cm...
Michael