Hi Don and welcome to the Q&A Board.
You are correct in stating that there are adapters that will connect certain lens mounts to certain camera mounts. In doing so, some modes on your camera will not function. That's often something you can get around though by shooting manually, etc. I don't have first-hand experience with Canon but this article may help you:
http://photonotes.org/articles/eos-manual-lenses/Good luck.
