I too have a 50D and tried using LR4 tethered. It "worked" but not very well. One big problem that I found was that the transfer to LR4 was slow, and so I could take a few shots quickly, but after about 4, it slowed down to being unusable. I now use Canon's DPP utility, it keeps up. I then load them into LR4 with the standard import function.