Is my 300 f/4 focus clutch failing?

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Vahur Krouverk Senior Member • Posts: 2,949
Is my 300 f/4 focus clutch failing?

On weekend I discovered that my 300 mm lens focus clutch is not working: when I pull it, it sets to manual focus, but does not focus to close range, only on distant objects.

Later I tried lens with other cameras with same issue and also tried 12-100 on same camera, which worked perfectly, so I'd exclude camera settings being culprit. If I set MF assist focus indicator, then I can see that full turn with clutch pulled changes only small part of focusing distance on longer end. I checked lens firmware, it's latest and I also tried to clean contacts. Setting on camera manual focus works as expected, everything else is working as well, just seems like pulling clutch does not change focus ring throw to manual focusing range but uses same range as if it were in-camera manual focusing.

Most likely lens is showing its age (7 years, I think) and needs service, but I thought that I'd ask here if anyone had similar case and it's caused by some obscure setting?

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