Best glasses: abbe value and optics?
david
Durrant) wrote:
> In article <38093...@bonaparte.pixi.com>,
> "Carl Jung" <anim...@hotmail.com> wrote:
>
> >The optician who made last pair said that high index with either a spherical
> >or aspherical design(I can't remember what he said!) can be excellent. He
> >recommended Seiko lenses. I'm still skeptical.
>
> No high index plastic even comes close to matching CR39's Abbe Number. Ask
> the optician what the numbers are - if he doesn't know off-hand, he should
> be able to look them very quickly.
>
> Paul
Having been through this previously myself here are a few abbe values for
you. I previously gathered these from posts to this board and the web.
Index Abbe
CR39 1.499 58
Sola Spectralite 1.537 47
Seiko 1.56 42
Seiko 1.60 37
Pentax 1.6 36
Optima Hyperindex 1.66 32
Poly Carb 1.586 30
My correction is almost -10 with minor astigmatism in both eyes. I
purchased frames with smaller lenses, the sola spectralite with a 1mm
center, AR coating, edges polished. Considering my correction the edges
are fairly thin, the glasses are light and they look fairly decent. The
optics are quite good. Prior to buying these glasses I used to buy
glasses from Lenscrafters, Vision World and that ilk (in high index they
only sell polycarb). I had totally given up on reading at night as my
eyes simply got to sore. That's all better now.
Carl Jung
index (1.66) aspheric lens are. From their literature you'd think this was
the "second coming" of lens technology putting it head and shoulders above
the competition. Well here are the numbers:
Index Abbe
Vizio plastic 1.66 32
Vizio poly ? 30
These really are not spectacular numbers. Am I missing something here? In
looking at their info on the net, it shows them comparing the maximum area
of sharpness on ViZio verses another brand poly lens and it walks all over
it. Doesn't abbe value predict overall area or viewable sharpness and
chromatic aberrations?
----------
In article <dcmiller1-171...@jdsl236.mpls.uswest.net>,
Paul Durrant
"Carl Jung" <anim...@hotmail.com> wrote:
> Index Abbe
>Vizio plastic 1.66 32
>Vizio poly ? 30
>
>These really are not spectacular numbers. Am I missing something here? In
>looking at their info on the net, it shows them comparing the maximum area
>of sharpness on ViZio verses another brand poly lens and it walks all over
>it. Doesn't abbe value predict overall area or viewable sharpness and
>chromatic aberrations?
I suspect that they're talking about monochromatic sharpness - i.e. only
comparing the shape of the lens.
A lower Abbe value will, of course, make anything off the optical centre
less sharp, given otherwise similar lenses.
Paul
Specs31
>of sharpness on ViZio verses another brand poly lens and it walks all over
>it. Doesn't abbe value predict overall area or viewable sharpness and
>chromatic aberrations
Your stuck on the abbe problem, the major distortions in a visual field of
the lens is NOT due to an abbe problem but oblique astigmatism :-) The
diffrence your seeing in all the lens is NOT that its an aspheric cut its an
ATORIC cut :-) thats what is helping eliminate , well thats a bad word it
neutrilizes the effects of an oblique astigmatism.
Optics are a little more complex then just considering "abbe" value, sadly
the majority of opticians out there do not seem to understand what exactly the
problems are and the "how & why" we correct the problems that come with using
non standard indexes.
JeffT
Specs31
well as yourself:-) is mixing what exactly abbe value and oblique astigmatism
is in a lens.
You seem to understand what chromatic abberition is but the "distortion"
everyone is mentioning is more due to oblique astigmatism NOT because of the
abbe value of the lens. The lens being dicussed i.e. the ViZio and the charts
you guys were talking about was showing what an oblique astigmatism effects the
visual field in a lens, how you try to neutrilize this effect is by
manipulating the type of front surface of the lens , in the ViZio case it with
an ATORIC design while the Spectralite and most of the other higher indexed
lens do it with the use of an aspherical surface compared to a spherical.
The thing to remember is the lens is NEVER going to be any better the the
dispenser will let it. :-) with out the proper fitting procedure and frame
selection you would be defeating the purpose of using an advanced design and
index. If you keep the frame as small as possible with a comfortable visual
field and keep the vertex 10 to 12 mm with the proper panto tilt in the frame
any of the lens do a fairly good job.
With your RX , any of the 1.55 to 1.60 range would be more then effective
(making sure to get an AR coating)
In fact I just put out a pair of Super16 from Seiko and have them right
here in my hands R-2.25 sph. L-3.00sph. in a Rembrand masterpiece frame 50x18
eye the edge thickness is 2.64 mm in the right 2.98 mm in the L (I guess you
can tell I have digital calipers:-) CT is 1.2 OU
But the chromatic effect is not noticable in the lens at all no matter
which angle I turn them , the AR coat is great about letting light travel
"through" the lens and not reflect everywhere.
With PROPER fitting and design selection and frame any of the lens would
work with your rx, the major problems you usually notice is reflections and
edge reflections not as much as the internal chromatic effects.
Just go with any of the aspherical or atoric designs and make SURE they are
fit properly and you should have no problem.
AND for goodness sakes invest in a good AR coating :-) With your RX I would
probably recomend a Spectralite if you walked into my store or called me if you
were a wholesale account. BUT if it is fit incorrectly even though your RX is
not really high you will notice a difference :-)
JeffT
Paul Durrant
spe...@aol.com (Specs31) wrote:
> Optics are a little more complex then just considering "abbe" value, sadly
>the majority of opticians out there do not seem to understand what exactly the
>problems are and the "how & why" we correct the problems that come with using
>non standard indexes.
Yes, but the original complaint was about chromatic abberation. I could
well be wrong, being just a user not a maker, but I thought the only thing
that would reduce the chromatic abberation was a higher abbe value?
Paul
SpecOPTICS
>well be wrong, being just a user not a maker, but I thought the only thing
>that would reduce the chromatic abberation was a higher abbe value?
Actually he was confusing the terms "chromatric" and oblique astigmastism.
He mentioned the "sweet spot" and that is where the optical center is and as
you move across the plane of the lens the natural effect is you get induced
astigmatism at an oblique angle ..non technical...it looks "blurry" or
distorted :-)
Chromatic abberation is that "rainbow" you see out in the periphrel of the
lens..the lower the abbe number the higher the degree the lens breaks light
down into natural lengths ..result, you see colored lines beside images. :-)
and that has the effect of "feels blurry kinda" but its just the lens breaking
the ambient light down into its natural wave lengths.
The whole idea as you get higher in index you try to use the high tech
surface designs to offset the problems that you get by using a higher
refractive index. (aspherical/atoric) also you try to make sure you get proper
fitting from a good optician that understands optics :-)
JeffT (spe...@aol.com)
"optician but prefers the lab work" :-)
Paul Durrant
speco...@aol.com (SpecOPTICS) wrote:
>>Yes, but the original complaint was about chromatic abberation. I could
>>well be wrong, being just a user not a maker, but I thought the only thing
>>that would reduce the chromatic abberation was a higher abbe value?
>
> Actually he was confusing the terms "chromatric" and oblique astigmastism.
Having re-read it, I thought he wqs complaining about both, but I could
have mis-read it.
> The whole idea as you get higher in index you try to use the high tech
> surface designs to offset the problems that you get by using a higher
> refractive index.
I may have mis-interpreted you here. Are you saying that induced
astigmatism is a function of the refractive index of the material? i.e.
that (other things being equal) glasses made from a 1.5 material will have
less induced astigmatism than glasses made from a 1.66 material?
Again, are you saying that aspherical designs are intended to reduce
induced astigmatism, and if so, would their use with a low index material
result in an even better result than in a high index material?
Intrigued, but confused :-)
Paul
Specs31
>induced astigmatism,
Yes, the index of the lens does increase the amount of astigmatism at an
oblique angle so what we do is use a aspherical design or atoric to help
neutralize this effect the surface design offsets the amount of induced
astigmatism. It's still there but it get "pushed out even further to the edge.
Thats why you always see opticians or OD's telling you to get a small as frame
as possible (that still looks cosmetically good) that outer edges are just a
huge distraction and even if it were there it would not be of any use to you.
>Are you saying that induced
>astigmatism is a function of the refractive index of the material? i.e.
>that (other things being equal) glasses made from a 1.5 material will have
>less induced astigmatism than glasses made from a 1.66 material?
Astigmatism at an oblique angle is just one of the give and takes you have
when fiddling with the index and using diffrent compounds of material, the way
you get the diffrent refractive indexes is done by making the lens in different
materials. The way these materials effect "light" and transmission is where you
have the problems, besides getting chromatic problems and oblique problems
internal reflections and loss of light transmission increase as you go up in
index :-) you lose 10% of light tranmission between a cr39 to a 1.60 index
lens(frenels equation)!! :-) Thats the reason you want to make sure you always
get a anti reflective coating as you increase index. Of course the majority of
opticians don't seem to know this is the reason :-)
>would their use with a low index material
>result in an even better result than in a high index material?
The majority of indexes are available in both a spherical and aspherical
choice :-) Sorry to say that most opticians don't seem to grasp the physics
behind optics so don't undertand the "hows" and "whys" ..most don't even seem
to know whats available out here in the market, specially the "chain" store
types who are limited in the choices they have to actually dispense.
We had a thread a few weeks back (I don't remember the name of it I think
it was headed undedr "atoric curves" or someting like that) where I went into
very indepth explanation of aspherical/spherical/atoric curves.. I think it was
Mike Tyner that I was talking to ask him maybe he remembers the thread. Do a
search on DEJA news it will explain alot of what we are talking about when
talking on curve design and high indexes and how it effects light.
People want "thinner" "lighter" material thats possible but we still
have to deal with the laws of physics, when you gain in one area usually you
lose in another but then you try to offset the internal problems that arise
(chromatisism,oblique powers,loss transmission) by using diffrent types of
surface design and coatings. All these things can be improved upon but combined
you still need to have an experinced dispenser who understands optics and frame
selection and fitting to help even further in the process. I can give you a
perfect set of lens and the OD's refraction is dead on but if the optician
fails then its a waste of time :-) All three sectors need to fit together to
get the best results.
Basically you have a degree of "clear" visual area in a lens, as you leave
that area there is not really much that can be done to enhance it your eye
rotates BUT the lens is sitting still so as you move across the lens from the
OC (optical center) across the plane of the lens the "power" changes as you
look through the lens at an angle (tada your "oblique" explanation :-) Take a
sheet of glass or, since you wear glasses hold them out in front look straight
through the lens then start tilting it ..see how things "bend" :-) thats the
same thing we are talking about. Of course thats the "extreme" case but it
gives you a good idea of how it works. The higher the power the less area you
have before starting into those oblique problems. Hence the higher indexes, the
advantage of high index is not really the wght. BUT you cut "less" curve to get
the same corrective power. there by less "fish" bowl so you have a wider area
before your lens starts to "warp" images. :-) that in conjunction with the
aspherical or atoric design helps neutilize it even into a wider field :-)
I could ramble on all day about optics but I gotta get back to work :-) Let
me know if I missed any spots or if you havn't found that thread on curves.
JeffT
Paul Durrant
spe...@aol.com (Specs31) wrote:
> We had a thread a few weeks back (I don't remember the name of it I think
>it was headed undedr "atoric curves" or someting like that) where I went into
>very indepth explanation of aspherical/spherical/atoric curves..
Thanks, I'll go and look it up.
> I could ramble on all day about optics but I gotta get back to work :-) Let
>me know if I missed any spots or if you havn't found that thread on curves.
Thanks for your posts. So far I've gathered that if I want the widest
undistorted field of view, I should
(i) Get a good optician
(ii) Get small frames that fit close to the eye
(iii) Get CR-39 spherical lenses
My prescription is around -6 and -2 astigmatism.
Because I work with computer screens all say, i find chromatic abberation
really irritating - I keep on wondering if it's the scren or my glasses!
Slight blurring off-centre isn't so troublesome - it's only when the colour
split that I really notice.
Paul
Carl Seutter
would do nicely and save money over a true aspheric. Add an AR coat to round
it off if you have lights behind you that can't be moved and show up as a
ghost image. Please make sure you are using correct screen placement and
distance guidelines. A screen located too high will result in reduced
blinking rates leading to dry eye sensations and headaches!
Carl
Paul Durrant <pa...@durrant.co.uk> wrote in message
news:B435E9DD9...@g3.durrant.co.uk...
Carl Seutter
Specs31 gave a pretty detailed response, so I'l just send a general info for
all recap.
THe standard for measuring eyeglass performance can be considered a
corrected curve crown glass lens. THis is the benchmark used by lens
manufacturers and opticians.
If you go to higher indexes, you experience higher amounts of chromatic
abberation off center. This is a correlation, not a causation. Some whizz
kid may figure out how to put out a high index lens with a lower dispersion
value. (Lower chromatic abberation and a higher Abbe value. Dispersion value
and Abbe Value are inverses of one another.)
Oblique astigmatism is due to looking through as curved surface. THe farther
you look off center, the greater the oblique astigmatism. Aspheric curves
reduce this effect somewhat.
Induced astigmatism is a result of both problems stated above. You can
reduce one error significantly only to be overwhelmed by the other. Finding
the balance for a given prescription and frame fit is the hard part and this
is where true opticians make their services and products worth the cost.
There are literally hundreds of options for most Rxs and every one has
numerous benefits and vices.
You are looking for an over-generalized statement that cannot be honestly
made. Each combination has merits and demerits. The right combinations for
your neighbor may not be the right combinations for you. Unless you want to
spend a few years digesting a ton of parameter specifications and real life
applications (this is the experience part) you won't be able to find the
closest thing to the "Holy Grail" of lenses. Even then, you'll realize that
glasses are like clothes in the fact that no 1 set will serve all purposes.
Think about it. Does a swimsuit work in Barrow, Alaska? Does a parka work in
Florida? Would you wear Spandex to a board meeting? Would you wear dress
shoes climbing a mountain? Every variance has it's purpose.
Figure out what you need for each situation and talk with someone
experienced enough to outline your options fully and let you make the
decision on what compromises are best for you. We all must live within the
confines of physics. Divine mystery does not apply to eyeglasses.
Carl
>
> I may have mis-interpreted you here. Are you saying that induced
> astigmatism is a function of the refractive index of the material? i.e.
> that (other things being equal) glasses made from a 1.5 material will have
> less induced astigmatism than glasses made from a 1.66 material?
>
> Again, are you saying that aspherical designs are intended to reduce
> induced astigmatism, and if so, would their use with a low index material
> result in an even better result than in a high index material?
>
SpecOPTICS
>Slight blurring off-centre isn't so troublesome - it's only when the colour
>split that I really notice.
>
>
You may want to step it upto getting a Spectralite lens, it's a good design
and the abbe value is fairly high(compared to others in its range(index))
One other thing to consider, when dealing with computer use work area I have
found that besides the "screen" other light sources were just as guilty causing
problems, besides the reflections on the screen those "nasty" overhead lights ,
lights from beside and behind you all seem to want to bounce off your lens!!
:-) Invest in a good anti-reflective coating as well. BTW do NOT let them UV
the lens inhouse make sure it is a factory UV (which Spectralite has at NO
cost) the uv inhouse solution tends to start to break down the substrate that
helps bond the AR to the lens surface. While the lens that has the solution
mixed into the actual lens material does not.
JeffT
rob...@nospam.com
>
>I'm on the holy grail for the best possible pair of glasses, my script is:
>
>RIGHT
>SPHERE -3.25
>CYLINDER -150
>AXIS 100
>
>LEFT
>SPHERE -2.25
>CYLINDER -225
>AXIS 75
>
>
>I've had a old pair of CR39 glasses that quite frankly seem hard to beat in
>optical quality, my definition of quality is low or no chromatic
>aberrations, wide, sharp, field of view-as you scan side to side, up and
>down. In other words what we call in the audio business as "sweet spot"
>where the music sounds the best, some speakers have a very wide sweet spot
>and some a very narrow-move your head 2" inches and the music goes from
>magic to muck!
>
>I've had a pair of 1.67 high index glasses made that gave me a headache in
>15 minutes, I think in part to sloppy fitting, however the problems with
>aberrations and a small area of maximum sharpness was obvious. I next had a
>pair of 1.6 high index glasses made (with a much better optician) the
>problems were dramatically lessened but it was still clear that my CR39's
>had 'em beat in overall quality.
>
>My question is, can any high index product claim to have as good (or even in
>the ballpark) an abbe value as CR39? I know Sola makes a product called
>Spectralite, that while not high index, is thinner than CR39 and claims to
>have an abbe value approaching CR39. How much different in abbe value would
>high index 1.6 or 1.67 be compared to a Spectralite and ultimately CR39. Am
>I correct in concluding that the narrower area of maximum sharpness is tied
>to abbe value?
>
>I know that having the glasses fitted and manufactured correctly is
>important but with so many variables such as frame size and human anatomy
>I'm not looking for theoretically what should be, I'm interested in what
>really is in the best in the real world.
>
>The optician who made last pair said that high index with either a spherical
>or aspherical design(I can't remember what he said!) can be excellent. He
>recommended Seiko lenses. I'm still skeptical.
>
>Any comments?
Carl
My audio specialist put a smile on my face when I listened to a pair of B&W
speakers. Let's see if I can make eyeglass lenses make you smile too!
I'll assume that you prefer not to use a very small frame that would make
regular plastic lenses reasonably thin and lightweight, and that impact
resistance is not an issue.
In your prescription, if you use Sola's spectralite material, you should
experience excellent clarity across the entire lens surface, almost the same as
your existing plastic lenses. Overall thickness reduction of 20 to 25 percent,
about 25 percent lighter. The left lens will be on the lower end of the
thickness reduction due to a 1.5mm center thickness instead of a 1.00mm center
for the right lens. (Your optician will explain this further, and by the way,
stay with that "much better optician")
Another excellent lens made by Rodenstock combines standard plastic and an
aspheric front curve. This results in a lens that is 20+ percent thinner but
similar in weight to standard plastic. Very little improvement in vision
compared to spectralite with your Rx, with a definite weight penalty. If your Rx
increases to 7, 8, or more diopters, or you simply want the best off center
clarity possible, consider this lens.
Because these lenses use different curves than your existing lenses you will
feel slightly disoriented the first day of use. The next morning they will feel
fine.
Do not fail to have these lenses anti-glare coated.
Enjoy!
Replace "nospam" with "execpc" for replies
Robert Martellaro
Optician/Owner
Roberts Optical
William Stacy
"rob...@nospam.com" wrote:
> On Sat, 16 Oct 1999 17:20:57 -1000, "Carl Jung" <anim...@hotmail.com> wrote:
>
> >
> >I'm on the holy grail for the best possible pair of glasses, my script is:
> >
> >RIGHT
> >SPHERE -3.25
> >CYLINDER -150
> >AXIS 100
> >
> >LEFT
> >SPHERE -2.25
> >CYLINDER -225
> >AXIS 75
> I'll assume that you prefer not to use a very small frame that would make
> regular plastic lenses reasonably thin and lightweight, and that impact
> resistance is not an issue.
>
> In your prescription, if you use Sola's spectralite material, you should
> experience excellent clarity across the entire lens surface, almost the same as
> your existing plastic lenses.
Almost is the functional word here. Nothing really comes close to the clarity of
ordinary cr39 plastic or (ahem) crown glass, especially in the lens periphery.
Keep the horizontal lens dimension as small as possible, and using ordinary, no
extra charge materials, you have the holy grail of ophthalmic optics.
Anti-reflection coatings are totally optional. Try it without first, since it can
easily be added afterwards if the reflections bother you. If you do buy into those
trendy aspheric lenses, then yes, you probably need the AR coat because of the
horribly flat surfaces they come up with...
Bill
Specs31
Actually Seiko makes a lens that is the best of both worlds (atleast in SV)
its the it has a spherical fitting button (I think its 10 or 15 mm wide) and
the edges are aspherical :-) Its a great lens but most of the OD/MD opticians
just don't seem to know about it. :-)
BTW this week was biketober fest we had around a 150,000 bikes in town, it
was a blast!! :-) I'm still in "recovery" mode....Both my brothers came down
with thier bikes and we had a blast. Did your son make it over here to Daytona
this weekend?
JeffT
rob...@nospam.com
>Almost is the functional word here. Nothing really comes close to the clarity of
>ordinary cr39 plastic or (ahem) crown glass, especially in the lens periphery.
Spectralite comes close. I wear a similar Rx and I can't tell the difference,
sharp and clear on the vertical and horizontal, and I'm plenty fussy about my
vision. So are the 1000+ clients I've fit with spectralite since it's inception.
The only difference of note is that the lenses stay positioned better with
improved comfort on the nose and ears due to the lighter weight.
>
>Keep the horizontal lens dimension as small as possible, and using ordinary, no
>extra charge materials, you have the holy grail of ophthalmic optics.
>Anti-reflection coatings are totally optional. Try it without first, since it can
>easily be added afterwards if the reflections bother you. If you do buy into those
>trendy aspheric lenses, then yes, you probably need the AR coat because of the
>horribly flat surfaces they come up with...
>
>Bill
>
If my glasses were comfortable with "ordinary, no extra charge materials", then
I would not recommend a change. If my glasses slip excessively, hurt my nose and
ears, Holy Grail is not the word(s) I would use to describe my eyeglasses. Since
Carl has been trying other "thin and light" lenses, it would seem that weight
and/or thickness is an issue as well as visual quality. He wants the best of
both worlds. In his prescription spectralite (and aspheric cr39 plastic, sans
significant weight reduction) provides this. Nothing trendy here, function only.
William Stacy
index, and very few aspherics, and very few of my patients have
significant nose or ear problems, and very few have any peripheral
distortion complaints. I do take care in frame selection and use mostly
modern small frames which are properly adjusted.
I do use spectralite when indicated, but not across the board, and
certainly not in weak Rxs. If big frames ever come back into style, my
numbers will shift, that's for sure.
Bill