OK, the speed booster changes the FL of the lens by 0.71x without changing the diameter of the aperture, so the max f/stop is changed to a larger one in terms of f/number
50mm f/2 (25mm diameter aperture), with speedbooster yields 35.5mm with 25mm diameter aperture or 35.5/25 = f/1.4
Put that on a 4/3 format body and you have the FOV equivalent to using
- 70mm FL on FF body or
- 44mm FL on APS-C body or
- 35.5mm on 4/3 body
In terms of DOF, at a shooting distance of 10'