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Science Forum Index » Medicine - Vision Forum » Zeiss
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| Paul via MedKB.com |
 Posted: Tue Jan 30, 2007 3:37 pm |
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I've been told that Zeiss lenses are best quality. Is that the generally held
view here?
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Message posted via http://www.medkb.com |
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| Mark A |
| Posted: Tue Jan 30, 2007 11:15 pm |
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"Paul via MedKB.com" <u12444@uwe> wrote in message news:6d1203efd8057@uwe...
Quote: I've been told that Zeiss lenses are best quality. Is that the generally
held
view here?
--
Message posted via http://www.medkb.com
There are two main things to consider when choosing a lens:
1.. Lens Material
2. Lens Design
Most lens manufacturers offer a lens in several different materials, and
they usually offer similar or identical materials. Each lens material has a
different index of refraction. Regular Plastic 1.50 (aka CR-39) is the
standard lens material. Getting a higher index lens results in a thinner
(and therefore lighter) lens, however the optical qualities of the lens go
down as the lens index goes up. The only exception to that is polycarb,
which has the worst optics of any commonly dispensed lens even though it is
not the highest index available. Avoid polycarb material. If you need safety
glasses, get Trivex instead (only available from the Hoya and Younger in the
US).
The lens design is also important, especially if you are getting progressive
lenses (PALs). Each manufacturer has several different models with different
designs, so just knowing the manufacturer alone will not tell you which is
the better lens. Sort of like saying which is better: Lincoln Continental
made by Ford, or a Corolla made by Toyota. A lot of people would say Toyota
is better than Ford, but not many would say Corolla is better than Lincoln
Continental.
If you are getting single vision lenses, focus primarily on the lens
material. Lens design (aspheric vs. spherical) is somewhat important if you
have a moderate to higher power Rx. Manufacturer is not as important.
If you are getting progressive lenses, focus on the lens material and the
lens design/model (which is proprietary to each manufacturer).
Zeiss has some premium lens designs like the Individual, and some very good
lens designs like the Gradal Top. So on that respect they are considered one
of the better lens designs. But not many would argue that the Gradal Top is
the best progressive lens available (although it may be entirely appropriate
for a low to moderate Rx).. |
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| Salmon Egg |
| Posted: Wed Jan 31, 2007 4:38 pm |
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On 1/30/07 7:15 PM, in article t6qdnSDwOotDlF3YnZ2dnUVZ_hmtnZ2d@comcast.com,
"Mark A" <nobody@nowhere.com> wrote:
Quote: Most lens manufacturers offer a lens in several different materials, and
they usually offer similar or identical materials. Each lens material has a
different index of refraction. Regular Plastic 1.50 (aka CR-39) is the
standard lens material. Getting a higher index lens results in a thinner
(and therefore lighter) lens, however the optical qualities of the lens go
down as the lens index goes up. The only exception to that is polycarb,
which has the worst optics of any commonly dispensed lens even though it is
not the highest index available. Avoid polycarb material. If you need safety
glasses, get Trivex instead (only available from the Hoya and Younger in the
US).
Thinner yes. Lighter, not necessarily so. I am not that familiar with
optical plastics. The old time glasses do not necessarily follow your rule.
In terms of refraction, it is n-1 that tells you how effective the material
is for bending light. When you take into account that "denser" glass has
higher index than "lighter" glass higher index may not mean lighter lenses.
I have not kept up with more modern developments. Using certain rare earth
oxides might give higher index without comparable increase in density. The
same may hold for plastics.
Bill
-- Fermez le Bush--about two years to go. |
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| James |
| Posted: Wed Jan 31, 2007 10:53 pm |
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"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C1E63E58.5ED7C%salmonegg@sbcglobal.net...
Quote: Thinner yes. Lighter, not necessarily so. I am not that familiar with
optical plastics. The old time glasses do not necessarily follow your
rule.
In terms of refraction, it is n-1 that tells you how effective the
material
is for bending light. When you take into account that "denser" glass has
higher index than "lighter" glass higher index may not mean lighter
lenses.
I have not kept up with more modern developments. Using certain rare earth
oxides might give higher index without comparable increase in density. The
same may hold for plastics.
Bill
Yes, I am only referring to plastic lenses, which probably account for 99%
of the lenses dispensed in the US. For a given Rx, if the lens is thinner,
then it is usually lighter simply because there is less material needed.
It is possible that a higher index lens would be so much heavier in terms
that the extra density would offset the use of less material. But that is
usually not the case. |
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| Salmon Egg |
| Posted: Thu Feb 01, 2007 3:00 am |
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On 1/31/07 6:53 PM, in article nJKdnZHpWZiEy1zYnZ2dnUVZ_rOqnZ2d@comcast.com,
"James" <nobody@nowhere.com> wrote:
Quote: Yes, I am only referring to plastic lenses, which probably account for 99%
of the lenses dispensed in the US. For a given Rx, if the lens is thinner,
then it is usually lighter simply because there is less material needed.
It is possible that a higher index lens would be so much heavier in terms
that the extra density would offset the use of less material. But that is
usually not the case.
The rule of thumb is that the index of refraction of a material is
determined by the valence electron density. Look at any decent book on
physical chemistry. Also different chemical bonds contribute to the index.
Double bonds contribute more than single bonds. The polymers that are useful
for optics can have various kinds of bonds that are found in organics.
Bill
-- Fermez le Bush--about two years to go. |
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| Mark A |
| Posted: Thu Feb 01, 2007 3:48 am |
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Guest
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"Salmon Egg" <salmonegg@sbcglobal.net> wrote in message
news:C1E6D021.5F0C6%salmonegg@sbcglobal.net...
Quote: The rule of thumb is that the index of refraction of a material is
determined by the valence electron density. Look at any decent book on
physical chemistry. Also different chemical bonds contribute to the index.
Double bonds contribute more than single bonds. The polymers that are
useful
for optics can have various kinds of bonds that are found in organics.
Bill
I don't need to look at a chemistry book. I was explaining the basics of
choosing a plastic lens to a consumer. Neither the consumer nor I need to
know chemistry. |
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| Sibir |
| Posted: Wed Feb 07, 2007 4:53 am |
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Yes they are if you buy Ziess's hype.
The quality from the major manufacturers are pretty much neck and neck. Pick
the design and material that works best for you and ignore the brand hype.
Carl
"Paul via MedKB.com" <u12444@uwe> wrote in message news:6d1203efd8057@uwe...
Quote: I've been told that Zeiss lenses are best quality. Is that the generally
held
view here?
--
Message posted via http://www.medkb.com
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