Sigma 120-300 F2.8 focus issues ? (1 Viewer)

Been having problems with back focusing with the Sigma 120-300 2.8 lens.
Target point out of focus and capturing 12-18 inches back from this.
has anyone had similar problems with this sigma lens ?
Has anyone had the same problems with the 300-800 lens ?
What experiences have people had with the Sigma service centre with related issues ?

Apologies for the number of questions but as you can imagine I would like a rough idea of what I am in for, in respect of standard of service !

I don't know about the problem that you're having and have never used that lens. But I did have problems with another sigma lens and they were very helpful on teh phone and quick to deal with the problem, so if it has to go back to them you shoudl be alright.

Never heard of a similar problem with this lens, but I don't own it - so I don't know from my own experience. If with other lenses you have no problem, then the fault is in the lens. I suggest to do an accurate test - by shooting a ruler from a tripod at controlled conditions. This will show you how much back focus you have (if at all) and will be used as a proof to Sigma. Could be the lens needs fine tuning (the electronic circuitry) or to be re-chipped.
Shoot the ruler @ a 45 degrees angle from above, extending away from you. Shoot at f:2.8, then @F:4 and then @F:8 and compare the results. Do the same for both extreme zoom settings. Use a shutter release cable or the IR remote control or delayed (self) shooting, not to touch the camera.
Sometimes back focus problems result from too-fast pressing the shutter release after the half press, before the camera has a chance to focus properly.

I hate to ask a stupid question but were you testing in single shot mode or mulit point focus.

I was using single focus, single shot and the problem has now been resolved by Sigma who were extemely helpful, they had a new circuit made up in Japan to compensate the figures and measurements I had calculated with charts and focus points, the lens is now working spot on at all focal lengths.
Good service.

raggetty said:

I was using single focus, single shot and the problem has now been resolved by Sigma who were extemely helpful, they had a new circuit made up in Japan to compensate the figures and measurements I had calculated with charts and focus points, the lens is now working spot on at all focal lengths.
Good service.

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Great, because the shot you showed looked on my monitor to be fantastic. I am thinking of getting it. Sometimes people use multilple focus and with my canon it will; lock on to a fantasy subject.

phili1 said:

Great, because the shot you showed looked on my monitor to be fantastic. I am thinking of getting it. Sometimes people use multilple focus and with my canon it will; lock on to a fantasy subject.

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Which shot are you refering to, I wasnt aware I posted a shot relating to this ?
Let me know.

raggetty said:

Which shot are you refering to, I wasnt aware I posted a shot relating to this ?
Let me know.

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Sorry it was someone else who had similar issues.