Due to long weekend and no fly-fishing conditions, I spent some time bird-watching and photographing (more the former). As the birds are quite far from the bird-watchtowers (I visit), only my long telephoto lens is suitable for this kind of photography.
However, a while ago I started to have focusing issues with my Sigma 120-400 OS HSM lens. It just started to hunt and even if achieved focus after about 10 secs it was often false focus. By time, the lens focusing deteriorated and during this weekend it went to non-existent. Of course, I could still shoot with manual focus, but in most cases, like hunting osprey, it was just luck or lack :).
I tried to work out in what conditions was the focus working (distance, light, aperture, ISO, etc.), but the whole thing was inconclusive.
A short consult of the mighty Internet revealed that Sigma announced some kind of design issue with their long lenses and offered fixes of those.
It is strange that the focus, in my case, deteriorated vs sudden failing. Anyway, I took the lens to the local Sigma service and they confirmed this issue. The estimated time to get the lens back is 3 days. So, I will update this blog soon and tell about my experience.
This is Sigma's announcement about the focus failure.
These are the affected models and serial numbers:
--- APO 50-500mm F4.5-6.3 DG OS HSM
--- Serial Numbers between 10633051 and 10972000
--- APO 120-400mm F4.5-5.6 DG OS HSM
--- Serial Numbers between 10574001 and 10972000
--- APO 150-500mm F5-6.3 DG OS HSM
--- Serial Numbers between 10674301 and 10972000
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