I have one of these macro lenses and when focused at infinity the image will shift slightly if you move the focus back and forth. I'm wondering if someone else with one of these could check theirs and post the results. I've relubed all the helicals and checked the tension on the turn stops and everything looks good. There are four helicals in this lens compared to the normal two surfaces in most other lenses so I'm wondering if this is just an inherent issue. Thanks!