<p>Jack, that lever in photo #1, if released, appears to allow the rear portion of the lens to be rotated relative to the front portion. In photo #6 you can clearly see red and white index marks that are out of alignment. The default position is when the two marks are aligned. BTW, the Adapt-a-Matic,, interchangeable, Tamron mount was superseded by the later Adaptall and Adaptall 2 mounts. The solution to your mount problem would be to acquire an Adapt-a-Matic mount for Nikon F.</p>