D5100 + 28-70mm 2.8 = No autofocus?

[KmH]

Yep. Nikon made a few AF-S D lenses, like the AF-S 80-200 mm f/2.8D. So AF-S D lenses have an internal auto focus motor, and an aperture ring.

Nikon quit making the AF-S 28-70 mm f/2.8D in 2007. The much more expensive AF-S 24-70 mm f/2.8G took it's place.