Complex sentence: An IMAX 3D theatre also is in operation near the former Expo 67 site at the Montreal Science Centre in the Port of Old Montreal; however, it's screen-size is nearly half that of the Pavilion screen.
Split into simpler sentences: An IMAX 3D theatre also is in operation near the former Expo 67 site at the Montreal Science Centre in the Port of Old Montreal. However, it's screen-size is less than half that of the Pavilion screen.