Hello, Jeffrey - Micro 4/3 has a 2x "crop factor" when compared to a full frame sensor, meaning the field of view for an equivalent focal length is twice as narrow. For instance, a m4/3 lens with a focal length of 25mm delivers the same field of view as a 50mm lens on full-frame.

In the case of the 40-150mm f/2.8 tele-zoom, 150mm has the same "reach" as 300mm on full-frame. Adding the TC-20, which is a 2x teleconverter, extends the reach to the equivalent of a 600mm full frame lens.