Check out this post from Instructor Insights>:
Last week I photographed poison dart frogs, as well as some other fascinating creatures, in anticipation of setting up a macro workshop where the subjects will be reptiles and amphibians. These frogs are intriguing. They are very beautiful and very, very small — one of them could sit comfortably on a dime — and it was obvious to me that I needed a flash because I’d be shooting at my smallest lens aperture, f/32, for maximum depth of field. The problem, of course, is that my 580 EX Canon flash sat too high on the camera body and the light would go over the top of the frog. Even with a specialized bracket that held the flash right above the lens, I was afraid the light wouldn’t illuminate the underside of my subjects and I’d be facing serious contrast issues.
I solved the problem with a ring flash. The Canon MR-14EX has two small flash units inside the ring, and this allows you to actually create a lighting ratio. The flash output is diffused for a soft look, and the only problem I knew I’d face was a reflection in the eye from the ring of light. This would have to be touched up in Photoshop — there was no way around it.
The macro workshop will be announced in my free newsletter that I send out every month. If you would like to sign up for this newsletter, visit my website: jimzuckerman.com and on the home page fill in your email address in the appropriate box.
(from: Macro Photography with a Ring Flash)