Aspheris plastic 1.74 or glass 1.9 index

[benlang]

hello. i am considering new glasses. i am nearsight-7 and -8 approx...what is difference in thickness between 1.9 index glass lenses and 1.74 asheric...i have read that glass is thinner and then contradictions saying glass min of 2mm in middle so thicker- obviously depends on how thicj 1.74 is for -8 in middle. also asheric is supposed to be thunner edges and make eyes look natural size But is 1.74 asheric better than 1.9 glass for -8......anyone jnow or know of online calculator or maybe just the formula

[apaul]

:idea: Speak to your optician
They are there to do this for you
If your not happy try another
Your not obligated to buy where you have your eyes tested!

Alan

[benlang]

thanks for the reply - appreciate the fact you took time out to reply but really this is not something that i have not already thought of...

yeah i ill speak to opticians but i am also asking for opinions on forum as i want a number of opinions - i do not trust anyone including opticians to not have a personal interest behind theuir opinion. I can not get many opticians opinion as each visit takes time etcv...i have already spoken to two opticians and one said just go for glass 1.9 coz we sell it and it is thinest [also most expensive not that i care baout the money] and another who said no way go for plastic 1.74 and when i asked if they sold the glass he said no - therefore on two occasions they have plugged whatever they happen to sell.
Therefore independent opinions much appreciated

[HarryChiling]

In the downloads section you can find a download of optical equations written by me in it their is a thickness calculator. It isn't going to be accurate because you are measuring a aspheric lens to a spherical, but it will give you an idea of the thickness differences. Also you can view an online version of it at www.opticampus.com the site belongs to Darryl Meister who takes pride in providing knowledge to opticians he is also a moderator in the opthalmic optics section of this board if you post your question their e may give you more insight.

[Dave Nelson]

You could also find a reputable, experienced optician who can guide you through the whole thing, then stick with him/her just like you would if you found an honest, experienced reputable mechanic for your car. Researching the products on your own is a good thing to be doing, but at the end of the day, you won't come close to matching the knowlege base of a good optician. Good luck.

[mirage2k2]

No one has mentioned abbe value. From what I understand 1.9 glass has a shocking abbe value! I would imagine the optical performance of a good 1.74, or even a Hoya 1.7, would be much better than a 1.9 glass. Also, 1.9 glass is very fragile ... apply a bit too much pressure in the wrong spot when your cleaning them and you might end up with a handfull of peaces.