do those focusing adapters get stuck easily? thinking of buying some and selling them
One of the CU adapters had impact damage (dropped?) and needed minor modification & repair to allow smooth operation. The main issue with the early adapters is their tendency to bind in focusing when the long and heavy lens heads such as 800/8 and 1200/11 are attached. Nikon designed the newer version AU-1 to overcome this issue. However, although AU-1 does not bind and provides a nice filter slot for rear filters, it is also
much heavier and less easy to operate hand-held (one might say it is lunacy to work with these contraptions hand held, and be correct, but the human mindset operates in mysterious ways so sometimes one tries the impossible).
The extremely non-linear (actually, rotational) movement of the aperture stop-down lever in these adapters confers a disadvantage for modern cameras and Nikon lists all these old lens/adapter combinations as incompatible with current cameras. However, we found a way to overcome this problem with minor side effects by judiciously special programming of the adapter CPU.