I am trying to understand the net effect of a tiny lens surface area such as cell phone versus the bigger surface area of dSLR lens. For example, if the same image quality can be derived from small surface area lens, then why don’t larger cameras create physically smaller elements for their lenses? Of course the physics of producing a focused image big enough to cover the sensor will differ on cell phone and dSLR. But is this equations simply scaled to the sensor, or does more glass gather more and better photons than small glass?