kkchang168

When I brought the second-hand cannon 1.4X extender, the salesman helped to cover the 3 pins and the AF works (I am using 7D+100-400mm f5.6). For 7D for AF, the f should be below 7, so when I use 400mm with 1.4X extender, the effective f is 7.84, so do not have AF. Although, AF works but the speed is too slow for capturing flying birds and practically it does not have AF.

kkchang168

Thanks Bob for your information. But f4 x 1.4 x 1.4 = 7.84 which is the same as my 5.6 x 1.4, so you mean you can AF with your set of equipment?

kkchang168

Thanks once again for sharing