Some more resources for testing your 24-105
Take note under the section "Principles of Optical Testing", Item 4 "An element just a bit off center can cause chromatic aberration, astigmatism, coma and edge softness"
http://www.canonrumors.com/tech-articles/how-to-test-a-lens/
http://www.lensrentals.com/blog/2012/05/testing-for-a-decentered-lens-an-old-technique-gets-a-makeov...
There is no hard data to back this up (and I certainly don't want to make any false accusations) but I have read lots of post and comments where people have had QC issues with the 24-105 lens and had to exchange it for a replacement copy. I was one of them. My brand new copy (not from a kit) had a huge air bubble in the front element. My second copy has been just fine. Maybe these numerous post are misleading because of the mass numbers of this lens in the field compare to other lens. Anyway I think the 24-105 is a fantastic lens and one of Canons very best valued lens.
After your testing, if you think you've got a defective lens, get it sent in to Canon before the warranty expires. Good luck and post your findings if you wouldn't mind.
