If they're anything like the Nikon -> Canon adapters, then they focus just fine to infinity, but you are stuck with stop-down shooting. I mount my old Nikon MF glass on a Canon AF body all of the time with two of these adapters (cheapies from eBay that work fine). Since Canon puts all of the metering smarts in the bodies, you can still meter in aperture priority and manual mode just fine. Since the Canon bodies are so slim, you can mount just about any other brand of lens on them with an adapter. (The reverse is not true in many cases. For example, you can't mount a Canon AF lens on a Nikon body without introducing some glass into the adapter, because the Canon lens would be too far from the film plane.)Originally Posted by Flotsam
There is no electrical or mechanical connection between the lenses (other than the actual mount itself), so you can't use shutter priority mode (there's no way for the camera to set the aperture on the lens), all program-style modes are out, and autofocus lenses won't autofocus.
A quick scan of eBay will show you which adapters are commonly available. If you can live within the limitations imposed, it's a great way to use old glass on a new body. With any luck I'll still be shooting with my Nikkor 105/2.5 for another thirty years, even if my FE2 gives up the ghost.