Boris, it's possibly no coincidence that the Pentax kit lenses are actually very good optically (esp. the 18-55) where the Canikon ones are apparently just disposable.
On Tue, Jan 7, 2014 at 11:58 PM, Boris Liberman <[email protected]> wrote: > Thanks for heads up, Bipin, but I have a question. It seems rather strange > to me that even the cheaper kit lenses that boast to have aspherical > elements would not use plastic in the composition. I wouldn't presume that > 18-55/3.5-5.6 AL was made all of pure glass... > > Anything I miss here? > > > On 1/7/2014 11:12 AM, Bipin Gupta 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. -- -bmw -- 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.
