So the other day I had to drive past the infmaous DD on the way to a studio to play around with some lighting. I'd heard the day before that DD had some cheap Rayflash ring flash adapters, so I just couldn't resist stopping in and getting one to play with.
I'd heard rumour that it only lost one stop of light compared to bare flash, but I wasn't sure what that actually meant, so I did some testing to see what kind of light I could get, and this is what I found...
There's plenty enough light belting out of the Rayflash for a head-shot @ 50mm on a crop sensor (ISO100, f/5)
... or even 70mm (ISO100, f/2.8)
For more idea on the power, I set a 580EXII to 1/128th power, camera on manual. For about the same crop as the mannequin shot (a little tighter) I could shoot at f/2.8, ISO100 and still be in the top section on the histogram (f/1.8 was probably a better exposure).
1/128th power, ISO800 @ about 2m at f/1.8 was blowing out foreground white paper, maybe slightly overexposed in the mid-ground (model), which gives you about another 7 stops to play with (without touching the ISO!). Much higher than my expectations.
The only thing(s) that bug me about it so far are that the actual ring is a little small - it'll fit over a 77mm sized lens, but, maybe not if its got a lenshood, and the actual ring of light (the thickness of the ring) itself is fairly small.
From what I've seen the 'pro' alternatives have both a larger and a thicker ring, so you get a bigger apparent light source, which (though I haven't done a comparison) probably gives you a softer light as well as the ringlight effect!
Click here for David Hobby's full review, with usage suggestions