My recollection is that virtually all modern wide-to-normal camera lenses contain aspherical elements, and that most of those are hybrid--a glass spherical lens with a plastic element cemented on to give it a complex aspheric shape.
The most notorious of these in Pentax land is the FA 28-70/4, whose aspheric element has had a tendency to separate over time. Rick On Jan 6, 2014, at 10:38 , Matthew Hunt wrote: > On Mon, Jan 6, 2014 at 10:11 AM, Bruce Walker <bruce.wal...@gmail.com> wrote: > >> That's a good question, Boris. Not being a gearhead I don't closely >> study the fine details of lens construction, but I assumed that only >> glass was hard and stable enough to be ground or milled into shape >> with the required tolerances. >> >> Does anyone know if plastic, or anything besides glass and coatings is >> used in the optical path of any K mount lenses? > > My understanding is that plastic elements are normally molded, not > ground. For aspherical elements, it's cheap to mold plastic, since you > only have to machine the aspheric shape in the mold, rather than each > element you produce. I think this is common for things like cell phone > camera optics. > > I don't know for sure whether plastic elements are used in Pentax > lenses or not. Someone on PentaxForums states (without proof) that the > 18-55 has plastic elements, and that wouldn't surprise me, given that > it's cheap and has "AL" (aspherical) in its name. > > Matt > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
