Directed to John and Jinny
When dealing with a wide aperture lens, as much as at all possible, use your center focus point on AI focus mode, and focus and shoot directly. Don’t focus-and-recompose. It won’t work as your plane of focus will fall behind your subject if you recompose even from a tripod. Your depth of field is really that thin. Instead, shoot a little wide and crop in post. If have a camera with Autofocus MicroAdjustment (I don’t) by all means run it through its paces either manually or using a software such as Focal.
Also, find out where your AF points actually are- the black boxes you see in the viewfinder are just a guide. The can be larger or smaller, or even not centered on the box. Test this by placing a target on a blank background, (blank enough for your camera to be unable to focus) put your camera in AI servo, and move the AF point around your target “feeling” at point point on all sides the camera snaps into focus.
That’s what I wish someone had told me when I started with a fast prime 🙂