Two feet away - focus looks great!
Four feet away - slight back focus ...
Seven feet away - focus is pretty bad
Ten feet away - focus is wayyyy off
I recently acquired a Canon 50mm F/1.4 lens and was excited to do some low-light shooting. It's amazing how fast of shutter speeds you can get with this lens, especially if you bump the ISO. However, my first shots came back pretty fuzzy, so I decided to see if there was a focus problem with this Canon lens.
As can be seen in the pictures to the left (click on them to see the full-res originals) the focus is very accurate for very close pictures like two feet. However, the farther away I moved, the worst it back-focused ... and it becomes a considerable amount even at less than 10'. Again, click on the images to see the full-res originals where it's very evident that the focus is off.
All pictures at F/1.4 and high shutter speeds, handheld using center point focus. The results were extremely repeatable ... and when I put the 85mm f/1.8 lens on the same camera, focus was dead on at all distances.
I.e. I think my testing methodology is sound and I even tried cleaning the lens and closing down the shutter a bit - same results. Something is wrong with this lens.