If you find an older lens that has the aperture ring on the lens, you can mount it to a non AF-S tube and mount that to the D3100. You will have no meters, so you will need to shoot in Manual, and read the histogram to get to the right exposure. Your EXIF will be missing data, so you will need to keep a shooters log, tracking the shot # with the f/stop used. Your EXIF will also be missing the focal length of the lens used. I currently have a Series E 50mm f/1.8 that I shoot with. It is trial and error and reading the histogram to get the right exposure. It would be no different than what I have outlined above.