Qool Rail 250 is an excellent choice for studio focus stacking work. It is capable of up to 100x magnification. 
 
Specificatioin:
 
Travel distance is about 170mm (full lead screw length is 250mm)
8mm diameter lead screw with 2mm pitch
Nema 23 0.9 degree bi-polar step motor
High quality membrance coupler
60mm round Arca-Swiss camera clamp with positioning poles
Dimension: L:380mm W: 80mm, H: tallest part 60mm
Weight is 2kg (exclude camera, but with camera clamp)
Smallest step size is 0.078125um (yes, that is um) with micro stepping controller (such as our USB and IR Remote controller), but practical step size is 0.3125um as we do not have equipment to test further.
Vertical lifting capability is 2kg max when power is set to 1.5A per phase via controller (both our USB and IR remote controller have such capability), horizontal load can reach as much as 7kg
 
Please note, price will vary depending on which controller you pick.
 
Buyer is responsible for all custom duties, tax, or VAT.