This is the helicoid focuser I have permanently mounted on my Olympus EM-5 and the Coastal Optics 60mm F4 APO via an F-mount to M42 adapter.
Cost: about US$80 from China
It extends by 16.59mm in total.
It is very solidly built and fairly heavy compared to some other helicoid focusers. It comes as a M42-M36 helicoid focuser and a separate M36 to Micro 4/3rds adapter. There is a little play in the adapter, but I still really like to use it. It will allow for infinity focus with the 35mm F3.5 enlarger lenses. I would definitely buy this again.