question?????

[bser]

does the refractive index have anything to do with the thickness of the lens.
IE will a cr39 be the thickess and a 1.70 thiness? with a crown glass 1.5 and POLY LENS TOO?? PLACE IN ORDER OF THIN TO THICK

[OPTIDONN]

The higher the index the less curvature is needed there fore you get a flatter thinner lens. In addition in most lenses the higher the index the more likely the lens can be processed thinner. So in a CR-39 you may get a 2.0 center thickness and in a spectralite you can get a 1.0 center thickness. I hope this helps. I'm sure others will do a much better job explaining it.

in order from thin to thick
1.70
poly
crown glass (but I have seen most glass thicker than cr-39. I don't know if they do that for structural support or what but it does have a higher index than cr-39)
cr-39

[Happylady]

If the center thickness is the same than the higher the index of the lens the thinner it will be. So assuming the same center thickness and rounding off from thickest to thinnest:

cr-39-1.50
crown glass-1.52
Trivex-1.53
Spectrilite-1.54
1.56
polycarb-1.59
1.60
1.67
1.70
1.74

There are also high index glass lenses available. Now sometimes a lower index lens will have a thinner center and will be thinner then a higher index lens.

The size of the lens also makes a huge difference in thickness of the finished glasses. The bigger the lenses the thicker they will be especially in minus lenses. Also the closer togeather someones pupils are makes a difference. The closer set the pupils the thicker the outside of minus lenses and the thicker the inside of plus lenses.

[ASenior]

Well said Happylady.

[Happylady]

Thank you. :)

[OptiStudent]

A higher index of refraction indicates a denser material. The denser a material is, the more it slows down light entering the material. The slower light travels through a material the more it is bent or refracted. Hence, a higher index lens is thinner than a lower index lens of the same power. The index of refraction is calculated by divinding 186,000 miles/sec (speed of light in a vacum) by the speed of light in the lens.

[QDO1]

A higher index of refraction indicates a denser material. The denser a material is, the more it slows down light entering the material. The slower light travels through a material the more it is bent or refracted. Hence, a higher index lens is thinner than a lower index lens of the same power. The index of refraction is calculated by divinding 186,000 miles/sec (speed of light in a vacum) by the speed of light in the lens. FYI: air has an indice of 1.0

I would be careful with the word dense. Density has more to do with weight, than optical properties. Perhaps use "optically dense" or "higher index materials bend light more than lower index lenses, so less curve is required to achieve the same corection"

[OptiStudent]

In optical theory I was taught that air is a rarer substance than say CR 39 and Poly is a denser material than CR 39 & air. Denser and rarer are the terminology that is taught. The density of a material is determined by its index of refraction.

[Darryl Meister]

There really isn't much of a correlation between physical density and refractive index, and the two terms definitely don't mean the same thing. After all, you can have a Polycarbonate lens that has a higher refractive index than Crown Glass but with half the physical density. You really shouldn't even use "optical density" to describe the refractive index, since this is also a specific measure (of inverse spectral transmittance). If I had to make up a "layman's term" for refractive index, "optical resistance" might do the trick.