Golden Rule wrote:
Okay, I have been working with the lens and have found that f2.0 is the widest I can go to get consistent tack sharp eyes. But I'm still going to check the calibration. This is from about 5 feet away and the eye on camera right is what I was aiming for and got it. Oops, it looks a bit dark on this post. Second one is about 10 feet away at f2.0
Glad you found an effective answer. With a fast lens, it’s often helpful to stop down just a little (assuming you have the light) for max sharpness, and to provide just a little more DOF and room for AF error without significantly affecting subject to background isolation or bokeh.