Misinformation 101

[Barry Santini]

industry to mean:

any unwanted light that diminishes contrast transfer.

I think this general definition holds for eyewear as well.

Barry Santini, ABOM

[shanbaum]

any unwanted light that diminishes contrast transfer.

You mean, like the scattered blue light in a fog or haze?

[Barry Santini]

You mean, like the scattered blue light in a fog or haze?

yes

[Darryl Meister]

There are certainly several definitions of "glare," though the kind you guys are referring to with scattered light is often called disability glare or veiling glare. Any stray light has the potential to reduce contrast sensitivity, or the modulation transfer function for optical devices, though the term "glare" is often reserved for light of a relatively significant intensity.

While the intensity of surface reflections is generally quite small (0.2 to 4%), these reflections can still be problematic in low-light conditions, as Robert alluded to earlier. Surface reflections of headlights can produce significant sources of "glare" compared to the background (night sky). Diffuse reflections of the face after being illuminated by oncoming headlights can also cause veiling glare -- and possibly even "discomfort" glare.

However, to Fezz's original point, statements regarding antireflection coatings and glare are periodically made in the context of settings that are not necessarily associated with low luminance levels, such as office work. For instance, I've seen statements of this type used as a caption to photos of computer users. Many computer users with poor workstation lighting may suffer from the effects of glare due to reflections from their monitor screen. Consequently, this type of statement becomes ambiguous -- potentially suggesting to consumers that antireflection coatings will alleviate "glare," in general, at their workstation, or even symptoms of other conditions that could be similar to the symptoms associated with glare (such as eyestrain from CVS).

However, there are situations in which glare from specular reflections can also become problematic in the office, such as reflections of sunlight from a window.

[Alan W]

If I might add my 2 cents . . . In the clinical setting, where the patient complained of glare, I found that in the majority of instances the offending source of light was oblique, whether diffused or not and that's what polaroid filters are so effective for. Also, although not nearly as prevalent as it used to be, there is an element of fluorescence on some lens materials (i.e crown glass). I haven't investigated possible fluoresence on the newer materials. But, as i said, it invariably turns out that the patient when asked where the glare is coming from, invariably seems to come from reflected surfaces that are not in the direct line of light. Having worked with several pilots, I've also dicovered that bright light that is diffused such as from clouds and other secondary light sources like fog etc. can be a problem that requires either polarizing filters or highly selective absorptive filters. The G-15 lens was created for the Air Force and has in its composition both selective filtration (grey) and small amounts of yellow/green that help in contrast discrimination necessary since the gray filter absorbs so much of the entire spectrum. I have yet to find someone, however, who can discern overly bright light from glare.

[DragonLensmanWV]

If you step back and look at lens edges it's possible to treat that as a unique cosmetic enhancement. By that I mean a higher powered lens, particularly a higher minus, with a flat edge highly polished and engraved or faceted can actually become a "work of art" that appears very much "intentional". I've made hundreds of such eyewear pieces selling them from samples that have been designed and crafted to look intentional. They can even be tinted on the edge as well as powder coated solid and in patterns. I believe there will be a resurgence of that technique which was very popular in the 80's. Some of us who have photos of Elton John's eyewear are examples crafted by Hans Feibig (of Optique Boutique) in Hollywood along with a few others.

My only problem with high edge polish and AR lenses is - why do you want to introduce more reflections into a lens that you are trying to reduce them in??
However, i do like a subtle edge tint. You can take your AR lenses, smooth the edge(not bright polish it) and a quick dip in Sahara and you get an edge tint.

[chip anderson]

Why not have the AR applied after edge polish? Then the edge would also be AR. Not to mention there would be no chance of scratching or otherwise screwing up the AR during polishing.

Chip

[AWTECH]

Chip said:

Why not have the AR applied after edge polish? Then the edge would also be AR. Not to mention there would be no chance of scratching or otherwise screwing up the AR during polishing.

Two reasons I would not recommend this.

First, you will not get equal coverage of the AR on the edge, this could cause the edge to look different than the AR. Processing cut lenses is a much larger task to manage since you have to make sure that each lens shape is held in the fixture correctly.

Second, you do not want to increase light transmission on the edge. The polishing already increases the light transmission from the dull unpolished finish.

[Alan W]

Rimless lenses with polished edges are far more attractive than ones with a frosted (unpolished edge). 99% of my customers insisted that the frosted edge looked ugly. AR, including on the edge, increases the transmission of light and minimizes internal reflection. That's what AR is all about. I agree with Chip. Tinting the edge before AR was applied is esthetically much more refined, and in the case of womans glasses, a light diaganol blush in the lower outside corners softens the look of lenses . . . purple based if the lady has yellow skin undertones and VERY slightly orange on skin undertones other than yellow. All intended to carry skin tones forward to avoid the look of being behind a "glass" barrier. And, as Chip said, a touch of Sahara is great. I used to carry that lightly around to the lower outside corner at a diaganol for mens eyewear as it lent itself towards a more tanned look.

If all this seems too "foofy" I am reminded constantly that before designer eyewear, which brought down the barriers of the stigma of glasses, we sold "medical devices." Now, just as human looking artificial limbs, veneers on teeth, hair transplants, etc. are significant elements esthetically AND psychologically, we are obligated to make eyewear as esthetically human as possible.

I'm reminded of the old timer who said I have no business putting a "blush" or "eyeliner" tint on lenses. Even if they are above and to the side of the line of sight. It is detremental to good vision and optics. I discovered that the patient will decide that. Without exception, the owner of such eyewear shows them off proudly (as well as who made them!) and wants to own more like it. I havn't heard of an exam or aquity test yet that revealed any dangers.

That's our job....make em see better. Make em look better!

[AWTECH]

Alan W said:

AR, including on the edge, increases the transmission of light and minimizes internal reflection.

How do suggest you apply such AR to the edges?

Why would you want light entering the lens from a direction that the lens is not designed to manage?

If you have a "B" measurement of 30 and you have a curve on the top of the lens equal to a 4 base and a curve on the bottom of the lens equal to a 4 base, you have a pretty large plus power of light. Without going into a great deal of technical details this magnified light coming in a different direction creates many optical issues.

Properly produced edges without a high luster can look great and offer superior optical performance. I believe the customer should be made aware of the plus and minus to polished edges.

[Robert Martellaro]

Here's another one-

Super high index of refraction materials are generally lighter in weight than mid and high index materials.

[EyeFitWell]

Here's another one-

Super high index of refraction materials are generally lighter in weight than mid and high index materials.

?? Is that misinformation? Or information?
I recently learned about how poly can be much lighter than high index plastic (depending on the Rx) even though high index can be considerably thinner.

[jherman]

1/8 or a 1/12

[EyeFitWell]

Half of a quarter is 1/8

1/4 divided by two = (1/4)times(1/2)=1/8

[Darryl Meister]

?? Is that misinformation? Or information?

It's a very broad generalization that may be right in some cases, and wrong in others, depending upon factors such as refractive index, density, minimum center thickness, prescription, blank size, etcetera.

[Robert Martellaro]

I recently learned about how poly can be much lighter than high index plastic (depending on the Rx) even though high index can be considerably thinner.

Right.

Trivex, Finalite, the newer Seiko 1.6, and poly are lighter in weight than 1.67 and 1.74, even in very high powers. The key is the lower specific gravity- low 1.20's for poly and some of the 1.6 materials, and 1.11g/cm3 for trivex. The only exceptions might be the atoric designs that have some asphericity on the ocular surface like the Vizio and Optima, (1.74 atorics are still(?) unavailable in the US), and with large eye sizes, although if you're trying to minimize weight I doubt you'll put a -10 in a 60mm eye size.

[Cherry Optical]

Right.

Trivex, Finalite, the newer Seiko 1.6, and poly are lighter in weight than 1.67 and 1.74, even in very high powers. The key is the lower specific gravity- low 1.20's for poly and some of the 1.6 materials, and 1.11g/cm3 for trivex. The only exceptions might be the atoric designs that have some asphericity on the ocular surface like the Vizio and Optima, (1.74 atorics are still(?) unavailable in the US), and with large eye sizes, although if you're trying to minimize weight I doubt you'll put a -10 in a 60mm eye size.

I can't seem to get my mind to undestand this whole concept. Does there ever come a point where a lighter/thicker material will have a total weight higher than heavier/thinner materials? I've played around with some numbers and just can't seem to convince myself one way or another.

For example: Would a -15.00 Polycarbonate weigh less than a -15.00 1.70 HOYA lens?

Any help on this would help to put my mind at ease.

Regards,



Adam

[Darryl Meister]

For example: Would a -15.00 Polycarbonate weigh less than a -15.00 1.70 HOYA lens?

Actually, ignoring any special lens designs, the difference in weight is pretty negligible between the two for a typical blank size (50 mm). Here are some ballpark figures:

Polycarbonate at 1.1 mm Center = 14.7 g
Hoya EYRY at 1.5 mm Center = 15.0 g
MR-7 1.66 at 1.5 mm Center = 15.3 g
Trivex at 1.1 mm Center = 16.3 g

Note that Trivex is by far the heaviest, even at a reduced center.

[Cherry Optical]

Actually, ignoring any special lens designs, the difference in weight is pretty negligible between the two for a typical blank size (50 mm). Here are some ballpark figures:

Polycarbonate at 1.1 mm Center = 14.7 g
Hoya EYRY at 1.5 mm Center = 15.0 g
MR-7 1.66 at 1.5 mm Center = 15.3 g
Trivex at 1.1 mm Center = 16.3 g

Note that Trivex is by far the heaviest, even at a reduced center.

I would love to see the equation used to figure this out! My weak math skills were unable to create anything that resembles your findings.

Adam

[Darryl Meister]

I used my Optical Analysis program. There are quite a few calculations involved.

[Robert Martellaro]

Actually, ignoring any special lens designs,
the difference in weight is pretty negligible between the two for a typical
blank size (50 mm).

Agreed. To say that super hi-index is generally lighter in weight would be inaccurate, unless your comparing to cr39, and the lens manufacturers don't always make this so clear in their advertisements.

Here's what your really cool Optical Analysis program shows, using 50mm -15 plano BC with 1.5 centers.

Trivex 13.9g
Poly 13.7g
1.67 14.2g
1.70 13.9g
1.74 13.9g

Inputting a -6 on a 2 base 48 eye 1.5CT gives

Trivex 6.4g
Poly 6.5g
1.67 7.0g
1.70 7.0g
1.74 7.1g

I suspect there's some fudge factoring involved here, but my DOS EZframe
program mirrors the above pretty well, along with anecdotal evidence.

[jherman]

where's that plugged in?

[Darryl Meister]

The specific gravity for each lens material is stored automatically, along with the refractive index, Abbe value, and typical minimum center thickness (though you can change the minimum center thickness using the Input menu).

[EyeFitWell]

Here's one that (I hope) is something customers misunderstand and Opticians can set straight:
I don't need AR, because my computer screen is antireflective.
Someone told me today that another "optician" had explained this to her.
If the computer screen is antireflective, that keeps light from bouncing off the screen, making it harder to see the screen (like seeing your lamp reflecting in the TV). It does NOT keep reflections off your lenses. Only AR can do that. I am surprised by how often I have to explain this one!

[braheem24]

If you're trying to get a lower index/lower specific gravity lens to be lighter then the higher index/higher specific gravity you'll have to calculate numbers closer to the plano range.