An FD mount is the type of mount that Canon used before the now current EF and EF-S mounts. Lenses with FD mounts are manual focus only. When Canon needed to introduce auto-focus lenses, they had to create a different mount to enable the technology. FD lenses aren't exactly obsolete, but they're a hell of a lot less useful than EF lenses with autofocus (assuming autofocus works).


EF lenses will work on all newer Canon cameras. However, EF-S lenses will only work on Canon cameras with APS-C sized sensors (which are smaller than their full-sized cousins). APS-C sized sensors are found in the Canon digital Rebels, xxD series, and 7D. Cameras with APS-C sized sensors can use EF and EF-S lenses, but full-frame cameras can only use EF lenses.