My favorite portrait lens is the Nikon 50mm 1.4G. I love the light and what it is capable of. My problem with it is that on my D90 the AF is sometimes horribly slow, and in many cases (mainly low light) I can't auto focus at all. I use AF lock as much as possible, but for many shots I really wish I could just use manual focus. The problem is that I'm usually wrong about whether my subject is in focus or at least completely in focus. So my question is...
Are there any recommendations you can make for training my eye to be sure my manual focus is accurate? Any diopter adjustments or calibrating tools? Any eye exercises to train myself to recognize a true focus?
I know that I would probably have better AF performance on a more expensive body, but for now I think it's good practice to train myself in manual focus anyway. Thanks for any assistance.