I ordered the Ef 12 II extension tube from B&H and have not received it yet, and i found out that there was a larger extension tube ( EF 25). My Question is should i keep the Ef 12 tube or return it and pay the 40$ more for the EF 25? I have Rebel Xt with 28-135mm Canon IS, 100mm Canon Macro, 100-400mm Canon L Is lens. I asked a question the other day about adding a canon 1.4x extender to my 100-400 lenses and the responses i got were great i wanted to say thank you. Alot of the comments said that it the AF would hunt if attached to the extender. I am kinda new to photography and I'm not up on all the terms and didn't quite know what that ment. They also said to tape down the 3 left most pins on the extender. Would i use regular tape? And would this cause any problems Sorry for the loaded questions. I'm making these purchases because i will be taking photography classes next semester and i want to have some good hardware. I have found this site to be very helpful. I will be writing again to ask about what lenses you may recommend that i get, a( shoot alot of outdoors and some of my sisters volleyball games) and a flash mount for my camera for my 430 flash.