Here’s a great idea for a DIY DSLR ring flash, use fiber optics to transmit the flash light from your DSLR’s built-in flash to a ring.
This is the best method I have seen so far as it uses no external LEDs but just fiber optic cables to transmit light.
For flash purposes, this light source is of course a regular flash unit, and the other ends of the fiber optics cables are fitted in the circular outline of the ring flash, that is, where other DIY people have placed LEDs. Unlike LED constructions, however, this construction allows the camera to adjust its flash intensity automatically, and it doesn’t require a power supply. Also, with a large number of fibers, the light should be very evenly distributed, possibly eliminating the need for a diffuser.