Hmmm, I may be talking out of school here because I will be the first one to admit I am painfully ignorant of pretty much all of Nikon's DSLR's except the D700 (and to be honest I am pretty ignorant of about 85% of what my D700 will do because I don't need it) but since the D5100 does not have an aperture sensing prong/ring like many other Nikon DSLR's, it is true that when the lens is mounted the camera would not have any way of knowing where the aperture ring was set. And with a Nikkor Auto H there would certainly be no way to transmit that kind of data to the camera. Or, for that matter. neither would there be a way any AI or AIS could either, with the exception of the 500mm f/4 AIS P which, although it was a purely manual lens, it actually did have contacts which transmitted aperture ring position. But if I am not mistaken, most digital cameras will fine tune the exposure based on how much light is coming through the lens, right up until the time the shutter curtains open.