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Medical Forum / General / Vision / January 2006New lenses have high chromatic aberation Ugh!
I have a very strong prescription. -15 range with astigmatism. I ask for the best in plastic lenses. I get high index aspheric with abrasion and reflection coatings. They always had strong off axis chromatic aberration. A year ago, what I got was incredible. Virtually no chromatic aberration. I could look out near the edge and still read the fine text on my screen. The coating was getting scratched so I ordered new lenses. These are nasty. Lots of color smear like the older ones. What baffles me is the optician tells me the same material was specified. She tries to adjust them and finally to no avail (I knew it would not make a difference). Clearly this can not be the same material. I guess the lab may have used low dispersion material before. The optician tells me the lab used both times is Hoya. Can someone tell me what the low dispersion material is? What is the index and Abbe numbers? IIRC, the optician says the material they specified has an index of around 1.6 Thanks for the help. John >I have a very strong prescription. -15 range with astigmatism. I ask for >the best in plastic lenses. I get high index aspheric with abrasion and [quoted text clipped - 15 lines] > > Thanks for the help. John It may be polycarbonate, which is 1.59 index, although I don't know of any polycarb lenses that go to -15.. Polycarb has the lowest abbe value (30) of any widely used material and is even lower than most 1.70 index materials. The advantage of polycarb is that it has high impact resistance and high tensile strength. Otherwise it is crap. Hoya, like other manufacturers, have lenses in many different materials, so you need to find out exactly what it is. >>I have a very strong prescription. -15 range with astigmatism. I ask for >>the best in plastic lenses. I get high index aspheric with abrasion and [quoted text clipped - 24 lines] > Hoya, like other manufacturers, have lenses in many different materials, > so you need to find out exactly what it is. Mark, I've been poking around the Web tonight and from what I found, It seems the good lenses may be Spectralite. They are a couple mm thicker than the ones I have with the color fringing. I think the lower index with higher Abbe should give me better vision from what I read. I guess the curving distortion will be reduced as well. I read that CR-39 is ideal, but would be very thick and not available in my Rx. Thanks, John > Mark, > I've been poking around the Web tonight and from what I found, It seems [quoted text clipped - 5 lines] > > Thanks, John Spectralite is a proprietary brand name for a 1.54 index lens sold by Sola or American Optical (who recently merged with Sola). Hoya would not have that exact same material. If you have progressives there is usually an etching on the lens that indicates the brand, model, and material, but otherwise it will hard for you to know what you have now. You might try taking it to Wal-Mart optical and see if they can id it. Are you sure you have a -15 lens power? I believe that Spectralite only goes up to -12.0 and not too many other lenses go to -15.0. >> Mark, >> I've been poking around the Web tonight and from what I found, It seems [quoted text clipped - 15 lines] > Are you sure you have a -15 lens power? I believe that Spectralite only > goes up to -12.0 and not too many other lenses go to -15.0. Yep, my eys are bad. Wouldn't even qualify for laser surgery. I notice the lenses I have now (good ones), the thickest part is 9/16", The older lens, is a bit under 1/2". In other words, about 2mm. Another test I did was touch a hot soldering iron to the side of the lens. The good lens is impervious to the intense heat! The older lens (with higher color fringing) give a odor similar to burning hair. Perhaps these properties would help identify the material. I'm starting to believe the good lenses are CR-39. I've never seen such freedom from chromatic aberration. John Hi John, the index in lens optics is the "refractive index" of a lens. Basically what it means for you is that the higher the index is (highest index for plastic lenses is 1.74 from ZEISS, Rodenstock, Seiko etc) the lower the Abbe number will be. The lower the Abbe number is the higher chromatic aberration will be. So the best lens would be a plastic lens with an index of 1.5 and an Abbe number around 52-58 depending on the manufacturer. This lens would have the best optic. Downside ofcourse is that these lenses with -15 dpt would be "monsters" (very thick) and mega heavy. The only manufacturer which produces a lens which almost gets ride of chromatic aberration and is thin is the German manufacturer Rodenstock (http://www.rodenstockusa.com/) . It's called the "Cosmolit 1.67 Impression Mono". It's the only mono lens which considers individual parameters and has an index of 1.67 so it will be very thin. Because individual parameters are considered chromatic aberration will be eliminated (even though the Abbe number is 32). I hope this could help you. Best Regards Christopher Zoett, BO > I have a very strong prescription. -15 range with astigmatism. I ask for the > best in plastic lenses. I get high index aspheric with abrasion and [quoted text clipped - 15 lines] > > Thanks for the help. John > Hi John, > [quoted text clipped - 22 lines] > > Christopher Zoett, BO Can you elaborate on "individual parameters" and how it can elliminate CA from a material with an Abbe number of 32? John JohnR66 schrieb: >>Hi John, >> [quoted text clipped - 26 lines] > from a material with an Abbe number of 32? > John The ellimination of CA occurs through special calculation of these Individual parameters: - pantoscopic angle - fitting height - base curve - lens form - frame dimensions - back and front surface optimizing - frame sag The only lens manufactures who can consider these parameters are Zeiss and Rodenstock. Essilor, American Optical, Sola, etc. say they also offer such lenses but they use total different parameters and calculation so you DO NOT get an individual lens. Since I guess you live in the USA or Canada, and don't need progressiv lenses yet, the Rodenstock "Cosmolit 1.67 Impression Mono" lens won't be available to you. Zeiss and Rodenstock offer lenses with consideration of individual parameters but only with progressiv lenses in the USA/Canada. >I spoke to the optician today and was told the lenses are Seiko w/ >index >1.67. No wonder! I told them I wanted minimal CA and the best vision >for my >perscription. I don't care if my lenses are 2mm thicker. >John my suggestion would be the ZEISS Clarlet 1.6 AS with Lotutec AR-Coating. This lens is thinner than a 1.5 and has good optics. Also take the best AR-Coating. Without this coating CA will be higher. But remember these lenses won't be 2mm thicker than a 1.74, they will be almost 1 cm (!) thicker. >my suggestion would be the ZEISS Clarlet 1.6 AS with Lotutec AR-Coating. >This lens is thinner than a 1.5 and has good optics. Also take the best >AR-Coating. Without this coating CA will be higher. >But remember these lenses won't be 2mm thicker than a 1.74, they will be >almost 1 cm (!) thicker. Thicker for sure, but not quite that much thicker. -15.00DS 1.5mm centers cut to a 41mm diameter using a plano base and a non-aspheric ocular curve. 1.74 index will be about 6.2mm at the edge 1.60 index will be 7.5mm, about 1.3mm or 20% thicker. Regards, Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr Robert Martellaro schrieb: >>my suggestion would be the ZEISS Clarlet 1.6 AS with Lotutec AR-Coating. >>This lens is thinner than a 1.5 and has good optics. Also take the best [quoted text clipped - 21 lines] > "An expert is a person who has made all the mistakes that can be made in a very narrow field." > - Niels Bohr sorry i forgot it the 1 cm was based on a lens with an index of 1.5 >Robert Martellaro schrieb: >> [quoted text clipped - 25 lines] > >sorry i forgot it the 1 cm was based on a lens with an index of 1.5 Christopher, No problem. I wasn't sure if the poster was following your example and was concerned that he might think his lenses would be so thick. By the way, welcome to s.m.v. Keep your kill filter handy if the quacks bother you. Regards, Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr >I have a very strong prescription. -15 range with astigmatism. I ask for the >best in plastic lenses. I get high index aspheric with abrasion and [quoted text clipped - 15 lines] > >Thanks for the help. John John, The optician can call Hoya to get the archived lens material info. However, it's possible, by improperly positioning the lens in front of the eyes, to induce more chromatic aberration in a high Abbe material compared to properly positioned lower Abbe lenses. I would check the monocular vertical and horizontal centers. Hoya's 1.70 index of refraction lens is usually my first choice for this Rx power. You will have more choices if you live outside of the USA. Hope this helps Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr >>I have a very strong prescription. -15 range with astigmatism. I ask for >>the [quoted text clipped - 44 lines] > very narrow field." > - Niels Bohr I spoke to the optician today and was told the lenses are Seiko w/ index 1.67. No wonder! I told them I wanted minimal CA and the best vision for my perscription. I don't care if my lenses are 2mm thicker. John
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