Wow, those are some great shots, @abigailblackstone. If you can do the tests that @nasa suggested then I think you’ll be able to narrow down where the problem lies. I wonder now if the lens doesn’t have a back- or front-focusing problem that would need micro-adjusting. If you have a friend with a camera that would allow that . . . I love @thefarmhand’s idea there.
@nasa, your comments are very logical and helpful; thanks so much for taking the time to share you experience with us!