Talk:Abbe number

Untitled
On the Cadmium page, http://en.wikipedia.org/wiki/Cadmium, in the "Applications" section, bullet (7) states that there is "no such thing as cadmium blue, green or violet". The Abbe Number article refers to "blue and red cadmium lines". What does this mean?

The article ought to specify whether lower or higher values are better if you want to avoid chromatic aberration. --Jsnow 00:54, 16 June 2007 (UTC)

The article mentions fluor-crown (crown glasses is a group of silicate glasses) but links to fluorite (which is not a crown and not a glass at all but crystalline calcium fluoride, which probably has a high Abbe number and is indeed used for this property). The article on crown glasses mentions fluorite as an additive. Fluorite as a glass additive is otherwise known for making glass turbid (e.g. milk-glass) which would be highly undesirable for an optic glass. The turbidity is likely to depend on amount, other constituents and heat treatment. Some kind of clarification is needed, what is the Abbe number of fluorite and are there indeed fluor-crown glasses?

—Preceding unsigned comment added by 150.227.15.253 (talk) 13:10, 22 March 2010 (UTC)

If the Abbe number describes the properties of a material, then it seems like it is possible to calculate the refractive index at any wavelength based on the Abbe number. Right? And if yes, how?--TeakHoken193.187.211.118 (talk) 11:22, 1 August 2008 (UTC)

Abbe number is best indicated by the greek letter ν (ni). The letter V is acceptable, though, and is indeed commonly used on lens catalogues, but somebody ought to clarify this within the article —Preceding unsigned comment added by 93.144.184.43 (talk) 11:26, 4 March 2009 (UTC)

The appears to be inconsistency in the naming of the green mercury line (546.073 nm). In the upper half of the page it's called the E-line but it's the e-line in the table at the bottom. The table is consistent with. The E-line is a close pair caused by calcium and iron. NoiseJammer (talk) 15:34, 6 August 2013 (UTC)

Wrong wave lengths in abbe formula?!
There seems to be s.th. wrong with the wave lengths and the corresponding fraunhofer lines, e.g. nC vs. nC'. See the german wikipedia site for more details. Can someone who knows better than me check this and correct it, if neccessary? Thanks. — Preceding unsigned comment added by 192.53.103.242 (talk) 11:28, 27 January 2012 (UTC)

Inconsistancy
Inconsistancy in two paragraphs, inconsistency between article and Abbe diagram picture provided.

This article stated

1)"Abbe The number, VD, of a material is defined as


 * $$V_D = \frac{ n_D - 1 }{ n_F - n_C },$$

where nD, nF and nC are the refractive indices of the material at the wavelengths of the Fraunhofer D-, F- and C- spectral lines (589.3 nm, 486.1 nm and 656.3 nm respectively). "

and then

2)"An Abbe diagram is produced by plotting the Abbe number Vd of a material versus its refractive index nd''. Glasses can then be categorised by their composition and position on the diagram. This can be a letter-number code, as used in the Schott Glass catalogue, or a 6-digit glass code."

If you defined Abbe diagram as using  Vd,why bother  mentioning  VD in the first place ??. Further the Abbe diagram picture showed here clearly stated using  nd with  is consistant with your 2) but contrary to 1).

Suggestion, get rid of

)"Abbe The number, VD, of a material is defined as


 * $$V_D = \frac{ n_D - 1 }{ n_F - n_C },$$

replace it with the more common


 * )"Abbe The number, Vd, of a material is defined as


 * $$V_d= \frac{ n_d - 1 }{ n_F - n_C },$$

as per Schott Glass work--Gisling (talk) 09:08, 21 October 2013 (UTC).


 * That was laying around for 9 years now. I corrected it. Palindrom~plwiki (talk) 22:22, 15 August 2022 (UTC)

Pronunciation
State how you pronounce Abbe.

(Footnotes following aren't mine.) — Preceding unsigned comment added by Jimlue (talk • contribs) 23:06, 1 April 2017 (UTC)

Modeling refractive index using Abbe number
So, as I understand it Abbe number is a single number to somehow express the shape of the $$n(\lambda)$$ curve using single number. Most specifically its convexivity? The selection of specific $$\lambda$$ is mostly dictated by 1) its practicality (easy source of monochromatic light), 2) its applicability (it covers wide and important visible part of spectrum), 3) utility (it is good enough approximation in intended wavelength range), 4) ability to compare dispersion properties of materials with different indexes of refractions. Or second derivative? How one would express approximated $$n(\lambda)$$, knowing n_D and V_D? My guess is that it is some kind of quadratic function. Sure, it is not theoretically backed by underlying glass optics, but it is very useful as a phenomenological model. The thing is I am not sure why three wavelengths are used. 2 wavelengths would be enough to create a number showing if the glass has low or high dispersion. So using 3 makes it hard to interpret intuitively what Abbe number actually is. I think the $$\frac{1}{n_F - n_C}$$, is easy to interpret by itself, it is using two extreme wavelengths, and is lower if the dispersion is high (because $$n_F - n_C$$ is high, if the dispersion is high, also it will always be positive and non-zero in real materials, but it can be very low in air, or very light materials, or zero in vacuum). The addition of $$n_D - 1$$, doesn't look to be serving much purpose, and in fact without knowing $$n_D$$ it doesn't allow one to know the shape of the dispersion curve even approximately. It appears to me one can construct vastly different dispersion curves, that has the same Abbe number, yet they will not be comparable to each other in any respect. 81.6.34.246 (talk) 06:28, 7 January 2020 (UTC)

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 * SpiderGraph Abbe Number-en.svg