Ring flash suggestions

[armatage]

I have just bought a Nikkor 40mm Micro lens for my D5100 as I wanted to get into close up/macro photography and so far I'm loving the lens. I will buy a 105mm at some point but as I want a Nikkor 10-24mm lens next it will most likely be next year.

Any way what I'm after is a ring flash around £50-£100 (£150 at a stretch), I've been looking but not sure which one to go for. Any suggestions for a ring flash please?

 

[armatage]

I plumed for a Welimex ring lite 670 for £160, will do for the moment. Quite pleased with the build quality but never came with a manual and one not downloadable, all though fairly easy to work out all the settings but cannot work out why the top swivels around, 0 to 180 degrees to the left and 90 degrees to the right (30 degrees steps). I've been looking into what this does but cannot find out what it does?

I have just bought a Hoya Pro-1 NDx16 (4 stops) filter as my Nikon D5100 has a max sync of 1/200 of a second meaning I have to use f16 to get the wanted exposure and therefore cannot get a narrow depth of field. This is my camera and not the flash.

Any idea what the swivle top does?