Re: Different types of plastic 1.6?

On Tue, 13 Jan 2009 18:40:27 -0600
Robert Martellaro <robopt@xxxxxxxxxx> wrote:

On Tue, 13 Jan 2009 23:15:30 +0000, Tony Houghton <h@xxxxxxxxxxx> wrote:

On Tue, 13 Jan 2009 15:03:08 -0600
Robert Martellaro <robopt@xxxxxxxxxx> wrote:

On Sun, 11 Jan 2009 15:51:09 +0000, Tony Houghton <h@xxxxxxxxxxx> wrote:

[OK with old 1.6 lenses, too much dispersion with new ones]

They should use the lens that you want- the lens that would be best
for you as an individual, within your eyeglass budget. If they don't
have what you need then go elsewhere. It's usually best to avoid the
discounters if you're looking for precision and good service.

I said to the dispenser right from the beginning that I had this problem
and he seemed to be quite aware of what I meant, but reckoned that I'd
be OK with their 1.6 now if I had been before :-(.

Right. But something has changed- either you're more sensitive to these
aberrations (unlikely), a significant change in Rx (seems unlikely) the lenses
are fit incorrectly (common), and/or they subbed Poly for 1.60 index.

We can rule out the first because I've still got the old glasses. I
could have just stuck with them I suppose, but I was fed up with the
frame. And is it my imagination, or do the coatings deteriorate in some
way and get harder to clean after time?

[Snip]

I don't think I've kept my prescription from 2002, but the changes have
been very minor in the last few years (since 2006 the only change is the
axis by about 5deg). It's annoying that I was able to have a truly
useful reduction in thickness for moderate extra cost back then which
doesn't seem possible now, but I don't know why.

A good optician will sort it out. It looks like Rx changes can be ruled out.

Finding a good one here seems to be the difficulty :-(.

I suspect there's more
profit in materials with lower Abbe values.

In general, as the index of refraction goes up the Abbe value goes down. Has
more to do with the physics of light than profit and loss.

Yes, but some materials are better than others at similar indexes. At
opticians in the UK I always feel like they're hard-selling
polycarbonate (usually dressed up in an impressive-sounding brand name).
The raw material can't be expensive because they use it for things like
roofs, while if there's an additional difficulty in machining it, surely
they've all got the right/improved tools etc by now and that cost is
largely amortized, but they can still charge the customer more for
"thinner, stronger, lighter".

--
TH * http://www.realh.co.uk

.

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