Poly Tale

[chip anderson]

I have a patient who is a contractor who has always worn 7/28 glass lenses in clear and Autum Gold for hunting. For some reason the lab got his new Autum Gold lenses ready in a couple days and took about 10 and an barrel of the usual "They had a breakage and are waiting on blanks" excuses. The patient decided he wanted a pair of shades in a hurry (I don't do hurry). He went first to Eye Masters got poly, complained about distortion, had re-made still had distortion. Then went to LC same problem 3 tries, then was told at LC "That's just Poly! We'll have to send them off and have it done in glass." As far as I know he is still waiting on glass.

I send this out just for your information and I don't need to know anything about the dangers of glass for cotractor/hunter, patient is aware and fine with it.

Chip

[Cherry Optical]

I have a patient who is a contractor who has always worn 7/28 glass lenses in clear and Autum Gold for hunting. For some reason the lab got his new Autum Gold lenses ready in a couple days and took about 10 and an barrel of the usual "They had a breakage and are waiting on blanks" excuses. The patient decided he wanted a pair of shades in a hurry (I don't do hurry). He went first to Eye Masters got poly, complained about distortion, had re-made still had distortion. Then went to LC same problem 3 tries, then was told at LC "That's just Poly! We'll have to send them off and have it done in glass." As far as I know he is still waiting on glass.

I send this out just for your information and I don't need to know anything about the dangers of glass for cotractor/hunter, patient is aware and fine with it.

Chip

Chip:

TRIVEX 7X28 is available. TRIVEX and PLASTIC would seem to be the natural transition from GLASS.

Adam

[chip anderson]

Point was patient insist on glass and can tell the difference in the optics of glass vs. poly, and probably trivex and CR-39. Glass is ground, does not have the negative optical charateristics of molded product.

Not that I was looking for a "safer product."

[Cherry Optical]

Point was patient insist on glass and can tell the difference in the optics of glass vs. poly, and probably trivex and CR-39. Glass is ground, does not have the negative optical charateristics of molded product.

Not that I was looking for a "safer product."

I too understand that you were not looking for a safer product. The recommendation of TRIVEX or PLASTIC was to better match the optical quality of GLASS.

We all know Polycarbonate (by any name) has the lowest optical quality.

Adam

[OPTIDONN]

I too understand that you were not looking for a safer product. The recommendation of TRIVEX or PLASTIC was to better match the optical quality of GLASS.

We all know Polycarbonate (by any name) has the lowest optical quality.

Adam

How so? Is it the birefringence? Even heat tempered glass has this and really how much does this effect the optical performance? Is it the chromatic aberrations? It takes a pretty strong power and looking way off the optical axis for it to have a significant effect on acuity. Poly has an abbe of 30 while 1.66 has an abbe of 32. I do agree that going from glass to any poly or high index material could cause a non-adapt.

[Cherry Optical]

How so? Is it the birefringence? Even heat tempered glass has this and really how much does this effect the optical performance? Is it the chromatic aberrations? It takes a pretty strong power and looking way off the optical axis for it to have a significant effect on acuity. Poly has an abbe of 30 while 1.66 has an abbe of 32. I do agree that going from glass to any poly or high index material could cause a non-adapt.

I am positive there are a number of Opticians that could get into great detail about the differences in optical quality between lens materials, I however am not that skilled at this point.

I do know there is drastic difference in ABBE value between GLASS, PLASTIC, and POLY. I also get to see first hand remakes due to changing lens materials (most notiably from GLASS to POLY). And my last quick and simple observation is that I have not seen any highly precise optical instruments that 'brag' of the use of polycarbonate lenses.

Again, I am always into be corrected, as that is how I learn, but I have yet to have someone explain to me how poly's optical quality is better than or equal to other lens materials without the use of qualifiers such as "high power" and "off axis".

Qualifiers are for sales people. The truth is for professionals.

Adam

[Chris Ryser]

I
........................but I have yet to have someone explain to me how poly's optical quality is better than or equal to other lens materials without the use of qualifiers such as "high power" and "off axis".

Having never worn any poly lenses ..........I read right here on the Optiboard all the time how inferior they are optically.

I do know as a fact that nothing really beats glass but that is in the past and we have to deal with what is available a a decent cost.

Today I decided to make test myself. I get a new computer with one of those big rectangular screens and a pair of SV poly lenses on my nose.

When looking straight at the screen without moving the picture is alright, when turning to the right or left the lines are moving. When putting the head down and looking through the lens at an agle, the screen becomes distorted and has lsot it's right angle lool.

Going back to my CR39 lenses everything is back to normal and by doing the same movements the effects I get with the poly do NOT exist.

I am now in a position to say that the optics of the equivalent poly could be rated at least as uncomfortable in a direct comparison. ( Maybe if I would wear them full time I would not see these defects anymore)

[OPTIDONN]

Poly is by far not the perfect material. There are other factors that contribute to non-adapts when switching from glass to poly. One is the weight issue. Going to a lighter lens does not always lead to patient satisfaction. The second is design, polycarbonate lenses use much flatter curves than crown glass and yes chromatic aberration is another factor.

"And my last quick and simple observation is that I have not seen any highly precise optical instruments 'brag' of the use of polycarbonate lenses."

And you probably never will. But the fact that glass is used in precision optical equipment may be a result of it's physical characteristics. Glass is much more durrable, in terms of scratching etc. not impact resistance, than polycarbonate but this is not a reflection of "optical superiority". Also the main argument against poly is it's low abbe. In some of the precision istruments there is so much chromatic aberration that achromatic doublets are used to minimize this.

"...but I have yet to have someone explain to me how poly's optical quality is better than or equal to other lens materials without the use of qualifiers such as 'high power' and 'off axis'."

Measuring 'off axis' performance of 'high power' lenses is one way to judge the optical performance of a lens design. It's like asking someone to explain the performance of a computer with out using computer terms.

To be honest I don't like wearing poly all that much and I do prefer glass. Just way to many people jump to the myth that poly has the poorest optic's and thats that without looking into the other factors or can't back it up.

[OPTIDONN]

Some of this could be a result of lens form. We could say that all high index lenses are optically inferior as a result of the flatter curves when compared to CR-39 or crown glass.

As a side note I love these ECP's that are of the opinion that glass is the worst lens material and obsolete.:hammer: It's either one extreme of the other.

[HarryChiling]

Dpower = [10 * ChA * Abbe] / [R * tan(A)]

Dpower = Power along the meridian
ChA = Amount of allowable chromatic abberation (in M.Jalie texts 0.10)
Abbe = Abbe value of the lens material
R = Distance to center of rotation
A = angle of rotation

If we use M.Jalie text and want our client to get no more than 0.10 D of chromatic aberration then the equation is

Dpower = [10 * 0.10 * Abbe] / [R * tan(A)]
Dpower = Abbe / [R * tan(A)]

Now if this same client wants the widest possible field of view let's give him 30 degrees of rotation and assuming the distance from the back of the lens to the center of the eyes rotation is 27mm:

Dpower = Abbe / [27 * tan(30)]
Dpower = Abbe / 15.59

So now lets see what the clients Rx has to be under for him to not have any noticeable effect from chromatic aberration in a poly lens which has an Abbe of 30:

Dpower = 30 / 15.59
Dpower = +-1.89 Diopters

Now what if you choose CR-39:

Dpower = 58 / 15.59
Dpower = +-3.72 Diopters

Crown Glass:

Dpower = 59 / 15.59
Dpower = +-3.78 Diopters

MR-8 (1.60):

Dpower = 40 / 15.59
Dpower = +-2.57 Diopters

Some people are sensitive to chromatic aberration and some are not, it is worthwhile for opticians to know how chromatic aberration does effect a clients vision.

[Cherry Optical]

In some of the precision istruments there is so much chromatic aberration that achromatic doublets are used to minimize this.

Please explain what/how an achromatic doublet is/works?

Adam

[OPTIDONN]

You can check out this link.

[HarryChiling]

Please explain what/how an achromatic doublet is/works?

An Achromatic Doublet or Triplet, is a optical system in which a second or third lens is placed in series with the first so that the chromatic effects of the second and third lens are equal to and opposite the first lens so that your lens system can be optimized for more than one wavelength of light also can be made to eliminate or optimize shpherical aberrations.

[For-Life]

Let us not forget about the processing of poly. Some processing is cleaner than others. I argue that you get an Airwear Aspheric or a Revolution lens you will have a much clearer lens than Gentex.

[MarcE]

Revolution lens you will have a much clearer lens than Gentex.

I think you mean "Resolution", right?

Statement is right on. I was comparing spherical stock poly lenses once and the distortion toward the edge of the Gentex lens versus Somo, Ce-Tru, and AO lenses was lots worse. And this is the kicker - the Gentex lens had a base curve closer to "ideal" than the other 2, which were made flatter. Is it in the processing? Or do I get an aspheric lens with the 'better' optical lenses, even though it's not packaged and priced that way?

I guess Essilor wants a product that makes their Airwear look good.

[Chris Ryser]

Some of this could be a result of lens form. We could say that all high index lenses are optically inferior as a result of the flatter curves when compared to CR-39 or crown glass.

Just look at the history of development of lens curves...................

1) plano/conevex or -concave

2) Bi/convec or concave

3) Meniscus lens +6.00D base curve

4) Coreccted curves

Hi index lenses did and still do have the flatter curves from which the corrected curves designs departed in the 1930'd and have ever since been considered as lower quality optics .............but thinner lenses which people have been buying because of esthetic reasons and not because of better vision. And this seem to be the the latest and newest wave in lens supplies.

[FVCCHRIS]

Dpower = [10 * ChA * Abbe] / [R * tan(A)]

Dpower = Power along the meridian
ChA = Amount of allowable chromatic abberation (in M.Jalie texts 0.10)
Abbe = Abbe value of the lens material
R = Distance to center of rotation
A = angle of rotation

If we use M.Jalie text and want our client to get no more than 0.10 D of chromatic aberration then the equation is

Dpower = [10 * 0.10 * Abbe] / [R * tan(A)]
Dpower = Abbe / [R * tan(A)]

Now if this same client wants the widest possible field of view let's give him 30 degrees of rotation and assuming the distance from the back of the lens to the center of the eyes rotation is 27mm:

Dpower = Abbe / [27 * tan(30)]
Dpower = Abbe / 15.59

So now lets see what the clients Rx has to be under for him to not have any noticeable effect from chromatic aberration in a poly lens which has an Abbe of 30:

Dpower = 30 / 15.59
Dpower = +-1.89 Diopters

Now what if you choose CR-39:

Dpower = 58 / 15.59
Dpower = +-3.72 Diopters

Crown Glass:

Dpower = 59 / 15.59
Dpower = +-3.78 Diopters

MR-8 (1.60):

Dpower = 40 / 15.59
Dpower = +-2.57 Diopters

Some people are sensitive to chromatic aberration and some are not, it is worthwhile for opticians to know how chromatic aberration does effect a clients vision.

Hey Harry, will any of these need adjusting/compensating at the stroke of mid-night on 12/31/06??? Sometimes, as my young son would say, you hurt my head with MATH!!:bbg: Chris.