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- Richard
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I've got what might or might not be a lens fault which is driving me mad - i cant decide whether to send it off for a service or not.
The lens in question is a Sigma 17-70 f/2.8-4 OS about 13 months old.
Its worth mentioning i've tried 5 other lenses on the body and no problem and this lens on another body and there is the same issue.
Im experiencing an occasional slight "miss" with the auto focus but only with certain types of shot.
Generally this seems to be on infinity focus and for most focal lengths and even stopped down to f/8 or lower.
I can take a batch of shots using the AF and these will be *slightly* out of focus to the point the picture is soft.
If i take the IDENTICAL scene, focussing on exactly the same spot using live view focus the image is much much sharper.
Problem is it comes and goes. I can take say 10 shots in a row and its perfectly find but i can also take 10 shots in a row and all will be out. This means i can't reliably replicate it.
I've tried OS on and off, tripod vs hand held, shutter speeds ranging from 1/20th to 1/800th and most apertures and its appearing on and off at random on all those.
Im getting confused now as ive run the focus test charts indoors and the lens comes out fine all the time, maybe 2mm back focus but thats it.
Is it worth me sending this lens off to Sigma to get it looked at or does the above just sound "normal"? I've never come across anything like it on any of mother other lenses or previous bodies. Yes i get some focus "misses" but never that many in a row or that often, and hand holding with live view the second after a bad one and it focuses in that normally.
Im reluctant to gamble £80 if they say its fine.
Is it even possible to have a lens that seems fine on close up tests that only has issues at infinity focus type scenes?
Has anyone got any idea what if any the fault might be? I can't do a microadjust as the body doesnt support it (but as its intermittent anyway i cant see this helping).
Its driving me nuts as ive now got a lens that i cant trust.
The lens in question is a Sigma 17-70 f/2.8-4 OS about 13 months old.
Its worth mentioning i've tried 5 other lenses on the body and no problem and this lens on another body and there is the same issue.
Im experiencing an occasional slight "miss" with the auto focus but only with certain types of shot.
Generally this seems to be on infinity focus and for most focal lengths and even stopped down to f/8 or lower.
I can take a batch of shots using the AF and these will be *slightly* out of focus to the point the picture is soft.
If i take the IDENTICAL scene, focussing on exactly the same spot using live view focus the image is much much sharper.
Problem is it comes and goes. I can take say 10 shots in a row and its perfectly find but i can also take 10 shots in a row and all will be out. This means i can't reliably replicate it.
I've tried OS on and off, tripod vs hand held, shutter speeds ranging from 1/20th to 1/800th and most apertures and its appearing on and off at random on all those.
Im getting confused now as ive run the focus test charts indoors and the lens comes out fine all the time, maybe 2mm back focus but thats it.
Is it worth me sending this lens off to Sigma to get it looked at or does the above just sound "normal"? I've never come across anything like it on any of mother other lenses or previous bodies. Yes i get some focus "misses" but never that many in a row or that often, and hand holding with live view the second after a bad one and it focuses in that normally.
Im reluctant to gamble £80 if they say its fine.
Is it even possible to have a lens that seems fine on close up tests that only has issues at infinity focus type scenes?
Has anyone got any idea what if any the fault might be? I can't do a microadjust as the body doesnt support it (but as its intermittent anyway i cant see this helping).
Its driving me nuts as ive now got a lens that i cant trust.
