An imaging optical system includes, in order from the object side to the image side, a first lens element, a second lens element, a third lens element, an aperture stop, a fourth lens element, a fifth lens element, and a sixth lens element arranged along an optical axis. The method utilizes waste heat from a cement kiln and the pyrolysis system includes at least a feed inerting section and a pyrolysis chamber. An input device inputs a MIN to be stored in the memory. RF feeds are electrically connected to the first, third, and fifth RF elements. The oxide may be an oxide which etches at a rate of at least about 100 \u212bminute with dilute HF at room temperature.