First off, I've been reading these forums for a couple months, and I think you guys and gals are great. I've got a little problem, and I was hoping you could help. I just bought a used 40d on ebay. This was an upgrade for my rebel XT. I also ordered 2 new lenses from Adorama, a 50mm 1.8 and a 55-250 IS. I got the lenses a few days ago, and I love them, especially the 50mm. So I get the camera today, take it out of the box, slap on the 55-250, and shoot a couple pics. Everything worked great. I put on the 50mm, and it wont AF. I made sure it was set to AF, I tried it on the rebel, works fine. Put it back on the 40d, nothing. So I tried the 18-55 kit lens from the rebel, nothing. Put the 55-250 back on and it works fine. I checked the manual, but I can't find anything. Why would one lens work but two others not? Any help would be great. Thanks.