Ring lights or flashes are a good addition to a photographer's bag. They allow the light hitting your subject to come from all around the lens, giving you smooth even illumination without shadows. They also give your human subjects desirable ring-shaped catch lights in their eyes. The downside is that they are typically expensive. Here I offer you a cheap DIY solution.
Step 1: Materials
-3D printer (optional but helpful)
-9v battery (you could go as high as 12 but I found this blindingly bright)
-9v battery connector wire
-velcro (only needed if you dont use a 3d printer)
-lens hood (only needed if you dont use a 3d printer)
Step 2: Design
My first step was to design and print a plastic ring that would thread onto my lens in the place where my lens hood would usually go. I left a notch for the wires. My backup plan if I couldn't get that to work was to press-fit and glue the halo light into the lens hood I already had, and drill a hole in the side. This is a great option for anyone who doesn't have a 3d printer.If you decide to go this route make sure you measure and select the diameter of the halo light you buy very carefully so it works with your lens.
Step 3: Fit
Once I successfully printed and tested that my ring would attach to the lens, I glued the halo light to it and attached a 9v battery connector to the wires coming off of it.
Step 4: Battery Holder
Once I was sure the light fit properly I downloaded a 9v battery holder design from thingiverse. Which you can find here.
I modified the design to allow me to clamp it in place underneath my camera using my tripod mount. (alternatively you can attach a piece of velcro under your camera body and to the battery and connect them that way.
Step 5: Light It Up!
When everything is plugged in, you will have a bright halo light for your dslr! You could easily modify this with a potentiometer to control the output of the light, and an on/off switch, which I will probably end up doing at some point.
If you found this useful please consider voting for me in the Photography Contest and the Lights Contest!
As always I welcome any comments or questions you may have.