[hotspur (Chris)]

How does one go about looking at if there is aback focus issue with a lens,and then getting it looked at?

I have a 70-200 F2.8 canon,and its a very fine piece of glass,I am happy with images,but around 10% or a little less,seem to have back focus.I have noticed when using its not as good as focusing as say my 400 L or my (17-55 F 2.8 which is the best I have ever had for focusing).

Recently I took some images at my son's year ten formal,my work friend asked if I could take some of his daughter,I took some in the hall,some were quite good,I then took some of the girl outside against a tree,but all 6 or 7 images were like the three posted,focus on the tree,I aimed at her eye.

The ones inside hall,pic 4 look ok,the only major difference,I had soft box on flash out side.

Any thoughts,about how I could think about this issue,most likey operator error-99% of lens issues are 98% user error.But the 17-55 F2.8 almost out guns the 70-200,this should not be so.

Images are as is out of camera.