BS I find with my macro flash I have to use exp comp as much as -1 stop
- with Canon its working, so it must be Nikon's fault
I have also had incorrect exposures with ring flashes, but my old Canon MR14-EX worked very well with exposure calculations and correction, so I can only hope it will be the same or better with the bigger, better (and more expensive) MT24-EX. Its actually for the butterfly photography where you normally have less time for a photo.
BV, in theory the same amount of light should be transmitted from a ring flash as from any other flash to obtain a correct exposure. The flash-heads are closer to the object and become quite hot, which might be a problem, but the brightness of the light should not be any worse. Also, I think it is better photographing them during the day when their pupils are closed for the bright sunlight. However, I try my best to do it as quick as possible since I don't want the snakes to become albinos...
We must remember that a photograph can hold just as much as we put into it, and no one has ever approached the full possibilities of the medium - Ansel Adams