I have bought quite a few helicoid focusers for use with various lenses (M42 and enlarger lenses). I will post about each helicoid focuser I have separately, and then combine them together for future easy reference. The information will include the various dimensions of each helicoid and my impression of how each works. This first post will be about the Hawk Factory M42-Nex helicoid.
1) Hawk Factory M42 to NEX adapter
It extends by 20.87mm in total.
Expensive but well built. Very little play in this mount. It comes with markings on the helicoid up to 21 (one for each mm of extension of the helicoid), which can be very useful. Very light. One of the best helicoids I own.