Originally posted by cbaytan I am sure rear one is made of regular glass we see as the back and front elements. But front one density is quiet low, looks like it is made of very light material almost like an acrylic. (shown with arrow)
Does anyone know what is made of? Thats interesting.
that would most likely be a hybrid aspherical element. most mass produced modern lenses have them, some manufacturers in the bottom the barrel lenses use completely plastic ones, then there are plastic cemented onto a glass surface which are more effective (these are the hybrid aspheric), and then there are lenses that have glass moulded aspheric elements which are more expensive and more effective at correcting various aberrations and then lastly and most expensive is the ground aspheric which is when a glass blank is ground down to it's final shape by lapidary techniques employed by machines, then polished and multicoated and assembled into a lens.
the Pentax 31mm f/1.8 limited has a glass moulded aspherical element in it's optical formula