The inelegant ring light rig:

[DrEntropy]

The light is an "El Cheapo" 'Kalimar' unit, from the film epoch. No hot shoe foot, a sync cord for a PC connection. My answer is to use the RF triggered slave with a PC adaptor as the means of firing it. Clumsy, but it works. For as little as it will get used, this was an experiment to see if we could get away with it without spending any money. Haven't checked yet to determine what the triggering voltage output is, so didn't want to tie it directly to my DSLR hot shoe via the adaptor. If it's a low enough output I can eliminate the RF stuff.

The "NIKON" sticker was put on there to keep snide comments from the "peanut gallery" at bay: "Hey! He's usin' cheap equipment!" kinda stuff. I called that: "Art Directors' Syndrome".

 

[Basil]

I have a similar flash from my film days. Mine has 4 separate lights arranged in a big square. Like your ring it mounts on the front of the lens. I used it mostly for macro back in the day.

 

[DrEntropy]

Checked trigger voltage and can eliminate the RF remote. 6.7V, so no issue with that. Found that the same unit was branded by several flash accessory companies including Vivitar ("Macro 5000"). Still need the hot shoe-to-PC adaptor.

Another concern is the weight of the unit on the front of an AF lens, so a Neewer LED ring flash is on the way, ring separated from the power unit. That mounts to the flash shoe on the camera. Much less stress on a plastic AF lens barrel.

More G.A.S. I guess...

 

[DrEntropy]

Got the Neewer LED ring-light today, much lighter than the old one, batteries and control unit mount on the hot shoe of the camera, loading the lens only with the ring. Much better IMO.

One "test" taken with the DX 40mm Micro Nikkor, camera in manual. ISO at 800, 125th at ∱16:

 

[DrEntropy]

Neewer unit has proprietary "snap in" adapter rings from 49mm to 77mm, they're plastic so care will be taken when screwing them onto the lens. So far my only criticism.