SIGMA 300mm f2.8 EX APO DG HSM PRIME LENS - CANON EF FIT ***MANUAL FOCUS ONLY***

When I first connected this lens to my test body and actuated AF, it cycled correctly from infinity to near focus and back again (I had the lens cap on). I can't get AF to work now. Whether there is a loose connection, or whether the looseness at the rear of the lens is affecting the AF I don't know.

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