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Any owners of the Sony 70-400 4-5.6 SSM II (A mount)? I have a question.

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I have just taken delivery of the above lens in good second hand condition for a nice price. On inspecting it the condition looks good as described. I notice that when I hold it and rock it gently back and forth there is a slight "thunk" noise which sounds and feels like something moving inside the lens. Not unreasonable for something of such heft, but it reminds me very much of how my Sigma 85mm sounds since dropping it (entirely my own fault) - which didn't affect the optics but did somewhat bugger the focus motor.


So I did a few tests. If I put the lens cap on (or otherwise point the lens at something it would struggle to focus on, like a plain white surface), zoom to more than approx 150mm and trigger the autofocus to rack it from infinity to MFD and back, the AF moves a LOT slower than I'd expect. It almost looks, going by the speed of what's in the distance window that the focus motor is struggling, though the speed is consistent. At first I thought I had the same issue as my Sigma, but it looks like this happens regardless of what angle I point the lens (the Sigma more or less packs up if I point it downwards). If I take the cap off, focussing appears to be mostly fast and consistent, but I haven't yet done a proper field test.


I am somewhat encouraged by the fact that if I turn the camera off with the lens at MFD, with the lens cap on, it returns to infinity focus very quickly so I suspect the AF motor is actually fine. I do however notice a very slight, though definitely present high pitched squeal from the AF motor usually when returning to infinity. Mind, I do have sensitive hearing so perhaps don't read into that too much.


Can anyone with the same lens perhaps test it for me with the lens cap on, at 400mm to see if this racking behaviour is the same? It's almost as if it slows itself down under challenging conditions at the higher FLs in hope of obtaining a lock. I bought the lens from MPB so have 6 month recourse but I don't want to go through the faff of returning it unless it is genuinely faulty.

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