On 19 Nov 2002 at 16:28, Brad Dobo wrote: > Ok, THAT much in error, I'm talking a good scratch to metal and a scuff on > plastics. > So not so hardy paint is robust and nice smooth non-porous metal it adheres to > well?? Why do my rooms walls mark so easily then? Now if they were plastic!!! > ;-)
The difference is that some of the plastic lenses are painted too, from my experience painted plastic lenses tend to scratch easier than painted meta1 lenses. The other thing is that the limited lenses aren't painted, they are hard anodised. Anodising is the process by which a tough oxide layer on the metal surface is subjected to dyes, this treatment is generally more ware resistant than the painted surfaces of most lenses. Now back to the plastic vs metal war, the arguments that I've seen so far are futile, materials science goes just a little deeper than plastic vs metal. For instance the physical characteristics of alloys of one base metal can range from crystalline structures that crumble under minimal loads to materials that can be used to produce long life springs. Heat treating such as annealing etc also changes properties. Plastics is a pretty broad term too, none are "good" or "bad" all materials have their place and are good if appropriately implemented. However from my observation the general rule in lens production is that the more expensive the lens the more the tendency to utilize metals in their fabrication. I have no problems in plastics being used in appropriate places but in most instances even thought the strength of the types of plastics used lens barrels etc is most probably very good it's guaranteed to result in a larger product as the strength to volume ratio will be higher than strong metal alloys. Now both the SMCP FA 20-35mm f/4 AL and the FA* 24mm f/2 AL lenses use polymers in an area that I'm far more concerned about and that is in the light path. The AL lens surfaces are plastic moulded on glass as far as I recall. This fabrication method is used to produce aspheric lens surfaces because it is fast and cheap, moulded or precision ground glass surfaces are better and have predictable longevity but are expensive to produce. Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications.html
