This is my new design to refine the focus below the 17.248µ microns according to my configuration for the Taka Epsilon 180 ED plus the Robo-focus, based on the Critical Focus Zone equation, CFS = fr squared x 2.2.
Taka Epsilon 180 ED have a f/2.8 squared x 2.2 = 17.248µ or 0.017248mm
The Robo-Focus unit coupled directly to the focuser shaft of the Epsilon 180, translates into approximately 25.400µ or 0.0254mm of drawtube motion.
So with this configuration I have a reduction of :1: 2.44, thus I have 0.00040µ or 0.00000040mm, now I can work within the theoretical focus zone.
The pulleys and belts were purchased on line from (http://www.indarbelt.es/html/main.htm) for about 26 Euros included transport. Parts list as follows:
Timing pulley primary with flange: 18 MXL 025 (Robofocus motor).
Timing pulley secondary with flange: 44 MXL 025 (drawtube focuser).
Timing belt: 96 MXL 025 (96 means the total lenght belt in mm).