Thanks to the new Micro Four Thirds System standard, the LUMIX DMC-G1 eliminates the internal mirror structure normally found in digital single-lens reflex (DSLR) cameras. Because the internal mirror system is absent, the camera's size and weight is half that of standard digital single-lens reflex DSLR cameras, weighing in at just 385 grams (0.85 lbs).

Without the internal mirror system, the G1's flange back -- the distance between the mount and the image sensor -- has been cut from 40 mm to approximately 20 mm.