Is there any SI unit for the base curve and refractive index???????
Is there any SI unit for the base curve and refractive index???????
The diopter is a measure of the focal length in inverse meters so it is an SI measure, as for index it is a standard measurement although the value can change depending on your countries refrence index.
If you're speaking of specific gravity, isn't the reference index the density of water?Originally Posted by YrahG
Refrence wavelength. :hammer:
Sorry, I was confused. I thought that the refractive index increased proportionally to the specific gravity of the material. After some "light" reading, I have found that this is not always the case. Thanks-:cheers:
Index of refraction is unitless (being velocity/velocity).
Right, it's the ratio between the speed of light in a vacumn and the speed of light in the media.
Which reminds me of a joke... the top ten cool things about driving a car that goes faster than the speed of light.
10. Sleep 'till noon...and still get to work by 8:00 a.m.
9. Doppler shift makes red lights appear green.
8. You can get to the good hookers before Charlie Sheen.
7. That deer in your headlights is actually behind you.
6. Cigarette butts don't land in the back seat...they land in last week.
5. You can make a fortune delivering pizza with the slogan: "It's there before you order it...or it's free".
4. L.A. to Vegas in 2 nanoseconds
3. Traffic enforcements limited to officers with PhD's in Quantum Physics.
2. License plate: "Me=mc^2"
And the number one cool thing about a car that goes faster than the speed of light...Chicks dig it!
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
To clarify, the "reference" for refractive index is a vacuum. Speed of light in a vacuum. In a 1.67 index material, light travels 1/1.67 times as fast as it does in a vacuum.
There's also the issue of reference wavelength, because light of different wavelengths travels at slightly different speeds in the same material. This reference is what varies by country.
Yeah, I was asking about the wavelengths used earlier, but apparently Harry C. is too disenfranchised to be lurking and answering.
What do they use? The emission spectrum of sodium or neon or something?
Care to pinch-hit, Charvak?
(BTW, is "Charvak" Vulcan?)
Hi Dr. K,
I'm not certain which wavelength is used, but I learned about it elsewhere on OptiBoard: http://www.optiboard.com/forums/showthread.php?t=24401
Lensgrinder seems to know that the US and UK use the "helium d- line" while Europe use the "mercury e-line". Wikipedia's table of indices of refraction http://en.wikipedia.org/wiki/List_of_refractive_indices cites a 589.29 nm wavelength for some materials, which appears to be the familiar yellow sodium D.
While searching for wavelengths, I came across this site: http://refractiveindex.info/abbe-num...material=CR-39 It looks like a great reference for the math behind Abbe numbers even if the data aren't complete. I'll reference that if I ever write a study quantifying the blurring caused by Abbe numbers vs. other abberations like oblique astigmatism or varying vertex distance.
Oh, and Charvak is actually my name, but I know it sounds kind of like a Star Trek word. It also sounds like a Pokemon, Charzard or something? It's Indian and pronounced more like Charwak, but I'm glad Indian people can't tell the difference between W and V and my parents went with the V. I guess I would have been an Ewok otherwise?
You da man, Charvak!
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