Sigma 17-50 2.8 focus issues?
Hello, I'm having difficulty getting consistent focus from a Sigma 17-50 2.8 purchased recently. Attached pix 2452 2454 suggest front focus, 2447 looks fairly well focused. I was focusing center point on the text '1770', 50mm, f2.8 for all. After dialing in -4 AF fine adjustment the focus seemed better but still inconsistent. I'd focus on objects around the room as well as the same '1770' text and while the area in focus in general moved back it wasn't consistent. Some were quite out of focus with both front and back focus apparent (I chose well textured targets that were at an angle to me). Two other lenses the Pentax 18-135 DC and Tamron 90mm 2.8 macro have none of these inconsistencies on my K5.
In another recent thread one response suggested it is better to return for warranty service rather than exchanging for another new lens but that was for centering issues. Would the same logic apply for focus issues? I've got an exchange set up but am wondering if my test approach needs improved or if I should go for warranty repair instead. Any helpful suggestions would be appreciated! thanks, Fred