Shelly Glaser: I have several pre-auto-focus, pre-CPU Nikon lenses, and they work fine on my Nikon D80 and D7000. The basic things to note -
(a) the lens must be of the AI type or later, or retrofitted to be AI-type (if made before 1977).
(b) The automatic diaphragm will work fine (close by itself at the movement of exposure and reopen after) but you should use it on M setting (Manual exposure - you select aperture on the lens and shutter speed on the camera - not too bad since you have instant display of the results) and focus manually, On the D700 (and I think also on the D7000) you can use A setting and let the camera select shutter speed automatically, though not all exposure measurement modes will work.
I think it is safe to say that non-CPU Nikon-compatible lenses (like Carl Zeiss and Samyang's), will work fine within these restrictions.
The problem with guesstimating your exposure on the Nikon D5100 is the camera itself- it is too automated to work with non-CPU lenses. That is why I bought the D300- it will work perfectlky with these lenses.