A T-ring is a simple adapter that allows you to connect your SLR or DSLR camera to a spotting scope or Telescope. It will screw on to any T-adapter, eyepiece or other digi-scoping adapter with standard T-thread (M42x0.75 metric thread).
With this type of photography you use the camera body only.
You can purchase T-rings from http://shop.northernoptics.co.uk