MZ I assume is what Olympus refers to their micro four thirds lenses by.... M. Zuiko Digital Lenses (Used to be Zuiko Digital Lenses for 4/3 cameras and just plain Zuiko for film).
Back on Topic. I am very impressed by what you can get out of that 75-300mm lens. Great technique and processing!
That lens surprises me at time. But honestly the biggest trick to the 75-300 is filling the frame with your subject and either having amazing long lens technique or keeping the shutter speed up.