If any of you are interested in using M42 lens on NEX directly. I have a blog post that may be of some interest to you especially if you have a Konica AR mount
The premise is the smaller size on the Konica AR to NEX adapter and together with the silver screw mount adapter for M42 to Konica AR, one can use the M42 mount lens with a smaller setup. Not that it shorten the overall length but it will look smaller due to the smaller AR adapter
more detail in blog post
When using Lens Turbo, here is my setup with genuine M42 adapter mounted inside the Lens Turbo adapter.
Super-Takumar 35mm f/3.5 mounted solidly with
genuine m42 to K adapter + Zhongyi Lens Turbo for k-mount
with nex 5n, LT, Super-Tak 35mm f/3.5
1/60 sec, 35mm, f/3.5, iso 320, -0.3 Ev
1/60 sec, 35mm, f/3.5, iso 1000, -1.3 Ev
I always prefer the genuine m42 adapter, if you have loose stopping plate or the screw on the 3rd party adapter, you can easily get your camera/lens stuck. I wrote about my bad experience with Bower adapter in m42 nightmare article with 3rd party adapters in which I was scrambling to free a stuck adapter from an adapter with loose stopping plate and screw.