Is this warranty replaceable?

[vvizard]

Hi guys, my name is Helge, and I'm a measurebator. I joined your club tonight, to find out if my Sigma-zoom shall be sent in for replacement or not. I shot... rulers! ;) And WOW! Did I freak out when I saw my camera front-focus? Yes I did! Do you blame me? Probably not.. Anyway, here's the shots, I would like some feedback on whether this is a warranty-repair/replace issue. All shots where taken on a tripod, at f/2.8 for the Sigma, and f/1.4 for the Canon. I used centre-point AF, and placed the middle of the point over the 13cm mark, and shot with self-timer. On the later Canon-shots I even placed the finger in on where I had focused. Should've done so on the Sigma too, but anyway, It was at the 13cm mark on all shots for all lenses. The Sigma was tested @ 200mm. Both lenses had a circular polarizer filter from HOYA.

First sigma-shot. Ruler in ~ 45 degree angle
http://www.127001.org/div_pics/canon_forum/sigma_ruler1.jpg
Where's focus here? 8? Off by 5cm.. not good :(

Second shot, ruler in a much more "laying" possition. Should be harder to focus correctly I think.
http://www.127001.org/div_pics/canon_forum/sigma_ruler2.jpg
This test I would thought should be harder for the focus. Think focus is at 10 here.. Three off, still not good.

So now I was freaked out, thinking the camera was focusing wrong. So I mounted the 50mm f/1.4 to try that one:

~ 45 degree.
http://www.127001.org/div_pics/canon_forum/canon_ruler1.jpg
Wow! Spot on! Oh, and I did a level-correction in Gimp on this one, that's the reason why the colors are way off the rest of the shots. Shouldn't affect the test though..

Laying possition:
http://www.127001.org/div_pics/canon_forum/canon_ruler2.jpg
and spot on again...

Should I send in the Sigma for replacement?

[CyberDyneSystems]

Do your focus tests WITHOUT the polarizer in better lighting...


A filter can throw off AF (in my case I had exactly the lens you have.. a Sigma 70-200mm f/2.8.. it was a perfect copy with reliable accurate focus.. but with a certain Hoyo UV filter the AF could be thrown waaaay out under certain lighting conditions...


Your test,. therefore.. is "poop" :)

[vvizard]

Ok, thanks. My focus hunted a lot with the polarizer shooting swans in sunlight yesterday. But that was either a total bummer or as good as it use to do. But never "halfway". But I will try the test again in the afternoon without filter. Now I'm off to the racing-field. Thanks for reminding me, I'll bring the standard UV-filter for that lens if the focus-problem with the polarizer continues

[KennyG]

Never test a lens with a filter, any filter.