This thing was made with Tinkercad. Edit it online tinkercad.com/things/02FqWoF8XqT
Designed to slip over the GoPro Hero2 lens, and allow you to screw the original lens from the polycarbonate case over it for Multicopter use. Saves all the weight of the full polycarbonate case, but still protects the main lens. Next step would be to print the main face ring of it to suit, then you can leave your original case intact.