In October, I bought a Nikon 24-70 f2.8 and I have been having major issues with getting sharp images with it. I didn't think the problem was with the lens at first, my first thought was camera shake, even though I almost always use this lens in a studio, at 1/250. So, I started using a tripod all the time. I thought maybe it was still an issue with the camera moving, so I tried using a remote to trigger it. Same problem. I ended up replacing the D300 I originally had with a D7100, but the problem still existed. So finally I sent the lens back to Nikon to have it fixed. It was under warranty, so they never really said if they found a problem, just said they made some adjustments, calibrated and cleaned it. Well, yesterday I did the first shoot since getting it back, and... same problem. I want to point out that I also have a NIkon 70-200 f2.8 and I get perfectly sharp photos with it, but I use that lens outdoors. So the only real difference is that with the 70-200, I'm shooting in natural light most of the time while with the 24 70 I'm using strobes (Einstein or White Lightning strobes). I cannot figure this out. The image I've attached to this is a 100% crop of a typical image. Virtually every shot I took yesterday has this same issue. It LOOKS like the camera is moving, but I don't see how. It's mounted on a Vanguard tripod, I'm positive that the focus point in the camera was directly on her face, this particular shot was taken at 1/250 at f4 but I've had the same problem at f5.6, f8 etc. Any ideas? I don't know what else to do, I cannot figure out why this is happening.