Thanks for adding some facts to the debate Bipin, and welcome back! I've been wondering where you disappeared to. Hope all is well.
On Tue, Jan 7, 2014 at 4:12 AM, Bipin Gupta <[email protected]> wrote: > Hello Bruce Sir, some aspheric lens elements are made by depositing > optical plastic on the glass. > Unlike a spherical lens element which is perfectly smooth and > roundish, asperical lenses will have a number > of jagged edges forming the lens curvature. > Also Dupleix lenses (two lenses glued together) no longer use Canada > Balsam due to separation and white > patches over time. But they use modern and durable man made glue which > is basically plastic compounds. > > I have had this lens separation and white patches (not fungus) on the > Pentax FA 28-70 f4 and a Tokina 20-35. > > Pentax DSLR lenses do not use optical plastic elements in the lenses, > though some manufacturers do. > > The fresnel lens under the penta prism is made from plastic. Its > purpose is to spread the light so that the corners > in the viewfinder are not dark. > > Some lenses in front of the metering light sensors are also plastic. > > Regards. > Bipin > > -- > PDML Pentax-Discuss Mail List > [email protected] > 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 [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
