One point I have not seen mentioned is the behavior over time of plastics
used in lenses (or for glazing and the like).
Historically, plastics degrade significantly over a relatively short time
and especially with exposure to sunlight. UV breaks down polymerization
chains and the transparency suffers. Clouding, crazing and a shift in the
color of the material isn't unusual. I'd be real concerned that the
investment in a plastic-element lens is temporary, no matter how good the
initial quality, for just these reasons.
Coatings don't seem to "stick" as well to plastics either. Both my
girlfriend and I have experience with this, in having the AR coating on
eyeglass lenses last less time than the prescription does. I won't buy
coated eyeglass lenses--at all--any more as a result, and last time inquired
how much extra I'd have to pay for glass.
And, relative to glass, plastic is soft. Much easier to get inadvertent
dings, nicks, scratches and the like.
---
Scott Gomez (yetanotherprouddinosaur)
-----Original Message-----
From: Skip Williams [mailto:skipwilliamsom@xxxxxxxxxxx]
Subject: Re: [OM] Trouble in OM paradise
You can see differences in very critical situations between today's aspheric
element equipped lenses and yesterday's multi-element lenses. The
differences show up especially well in situations where you see chromatic
abberations, coma, and astigmatism, like point light sources. Not all the
lenses, just the best.
<snip>
Skip imadinosaurandproudofit
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