Talk:Corrective lens

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[edit] Comments

Some of the explanations need better wording and more accurate descriptions. Maybe someone more knowledgable can help in this regard.MichaelGoldshteyn 14:48, 8 September 2006 (UTC)

I've tried with recent edits. Are there specific areas that need attention now?Garvin (talk) 10:19, 13 January 2008 (UTC)

Most people do not seem to be bothered by a slight or even moderate amount of chromatic aberrations. However, the choice of material and index are the only criteria that are available to the average consumer. Best base curve selection and even selection of aspherics and atorics for all material types are usually not provided as options to opticians, let alone consumers. Such decisions lie solely with the lab producing finished and semi-finished blanks.MichaelGoldshteyn 14:48, 8 September 2006 (UTC)


Removed this text added by 155.136.80.163: "Polycarbonates are typically manufactured from sheeps' bladders, which contain a specific diamino - benzoic acid molecule, relatively low in molecular weight, but relatively unwearing." which appeared under High-index materials (Polyurethanes) heading, since:

  • It has nothing to do with polyurethanes, as stated
  • If true for polycarbonates, which I doubt, since they are synthetic plastics, it should be added to the page on polycarbonates not corrective lenses.

MichaelGoldshteyn 15:27, 12 September 2006 (UTC)

Undid the change made by 71.136.6.98, who changed the Fraunhofer line type from the correct He to the incorrect Na. Clearly, said user did not go to the Abbe Number link and read about which Fraunhofer line is used for Abbe number references in the US (i.e.,He-D3 or more commonly the d-line, with respective Abbe number Vd ) and Europe/Japan (i.e., Mercury e-line with respective Abbe number Ve ).
References, in order of authority:

MichaelGoldshteyn 16:31, 3 October 2006 (UTC)

Q: Polycarb lenses are supposed to be more scratch resistant than most lenses according to other sites. The article states that polycarb lenses scratch more easily than most lenses. Can someone check this?

A: Polycarbonate in and of itself is not very scratch resistant. It is the hard scratch resistant coating that is almost always applied to the polycarbonate that gives it the scratch resistance often found in lenses made from the material. The reason that uncoated polycarbonate scratches easily is that it is a very soft material. This softness is what gives it much better impact resistance, since it bends rather than breaks. However, it is this same softness that makes polycarbonate easy to scratch by harder materials. See polycarbonate and also http://www.engineeringtalk.com/news/gad/gad192.html for more information. MichaelGoldshteyn 20:15, 19 December 2006 (UTC)

Aspheric lenses are not only for cosmetics, they provide better "picture". At least stright lines looks stright.

Curtis Williams, please correct your assertion that: This qualification is necessary since best-form spherics are always better than aspherics for an ophthalmic lens application. This assertion is incorrect! MichaelGoldshteyn 17:14, 25 January 2007 (UTC)

 What quality of lenses can be expected at "discounters" such as Lense crafters and wal-mart etc>?

[edit] Sphere "axis", irregular astigmatism

The axis defines where the two powers (sphere and cylinder) are located. The sphere is almost always 90º from the cylinder. (This is regular astigmatism, which is by far more common than irregular astigmatism where separations are other than 90º).

This is garbage! A sphere has no axis (besides the optical axis which points normal to the lens surface or into the paper plane of the diagram referred to here). Irregular astigmatism is somewhat a misnomer by ophthalmologist, as in a wavefront sense, "regular" astigmatism is simply the lowest order even aberration (does not change sign on the opposite side of the pupil) that can be corrected by a "cylinder", anything that does not fit in that scheme and causes "blurring" is called "irregular" astigmatism by ophthalmologists, while more correctly, different (higher) orders of coma (odd symmetry), astigmatism (even symmetry) and even higher oder spherical aberrations can appear, but the irregularity here is not related to any orientational angle.

However, it is known that in a typical population, certain orientations of regular astigmatism are more common than other ones. Maybe this kind of irregularity was meant here, but it´s not the usual meaning of that term. —Preceding unsigned comment added by 84.174.203.127 (talk) 22:26, 27 March 2008 (UTC)

[edit] Best form vs. free form

This qualification is necessary since best-form spherics are always[verification needed] better than aspherics for an ophthalmic lens application.

This cannot really be true in the strict mathematical sense, because mathematically, the spherical "best form" is only one special case of the a general "free form" surface. So, a "best form" is a restricted "free form" surface, hence, you reduce the number of available degrees of freedom to solve the problem at hand. With less number of free parameters, the result cannot be better than a more general solution. However, for reasonable metriks, it is true, that a flatter "free form" is likely not as good as the more curved spherical "best form"! 195.127.179.227 (talk) 15:34, 30 January 2008 (UTC)