Hi, I only own Canon lenses right now. I know about the mount systems and how EF-S lenses are only usable on the crop bodies. My question is what about Sigma and Tamron? How do you know if a particular Sigma or Tamron will fit a crop and FF Canon body? Here's my reason. I am heading to Mexico for a family vacation and have read a lot about the Canon 18-200 IS lens for vacations. It sounds like a great travel light, one lens solution. I have had people tell me to look at the SIgma 18-250 or Tamron 18-270 as an alternative. I know the Canon is an EF-S. Are the Sigma and Tamron limited to crop bodies too? I am likely to add a FF to my camera list this year. As for the vacation. I am trying to decide between getting one of these lenses or just carrying my 24-105L with me. I love that lens, but having 200mm could be nice too. I just do not want to carry a lot of lenses on this vacation.