Hi all, I am trying to understand this f-stop thing and getting no where. The question I have is when x brand produced a lens which says f2.8, L brand also has a lens that says f2.8, can we safely assume that both lenses have the same maximum aperture of f2.8 based on a certain measurement, barring the quality of the glass, practically will allow the same amount of light enters its iris? What about consumer camera that claims f2.8, such as the Panasonic FZ-series Leica f2.8 (420mm!!)?