06-03-2021 07:12 PM
This use to be true, But not anymore!
No, it is not faulty. The 2x extenders do not work with, or allow for autofocus, with any and all combinations of cameras and lenses.
It still holds true for the OP's EOS 7D DSLR camera.
06-04-2021 08:56 AM
John Hoffman's unofficial samples proves that a native lens can and does produce similar results, perhaps even a bit better, when cropped to tel-con status as the addition of the tel-con on the lens. So why bother?