Because the mirrorless cameras all have different sensor sizes, they also require different lenses to get the same angle of view from the same place. For example, if you and I were standing next to one another and I was using an m4/3 camera with a 150mm lens, if you were shooting with a Sony NEX you would need a 200mm lens to get the same shot.
|Angle of View
|35mm (FX)||APS (NEX, NX)||m4/3||CX (Nikon 1)|
(Warning: some values have been rounded for convenience in this table; * indicates a focal length not currently available in a format).
Note that manufacturers do not tend to use horizontal angle of view in their specifications. Instead, they use diagonal angle of view (angle across the diagonal of the capture area). That's not the way photographers think, though. Anyone can figure out what 90 degrees horizontal is (about an 18mm FX lens), but I don't many that can figure out how to apply 100 degree diagonal (also 18mm FX), especially when we have differing aspect ratios (3:2, 4:3, etc.).