Talk:Luneburg lens

Fish-eye attribution

I reckoned it was worth clarifying the fact that the attribution of the fish-eye to Maxwell is indirect. However I haven't restored mention of the alternative attribution[1] to Charles Anthony Swainson as it's not clear that this has been published in a reliable source (also, the stated grounds are unconvincing; the 'C.A.S.' could equally well attach to just the last solution of the set). --catslash (talk) 00:22, 25 July 2011 (UTC)

I agree, and I think that the current version of the text makes the attribution issue much clearer than the early versions did.

I added a "cite needed" request to the earlier claim in the article that the lens was first described by Maxwell in 1854, since it isn't clear to me if this refers to the problem set you mention or to some other publication that year. The date is confusing, since it doesn't agree with the 1853 first publication in the problem set. If the 1854 publication is just referring to the solutions to the problem set, we can make a duplicate link to the same reference.--Srleffler (talk) 01:15, 25 July 2011 (UTC)

What does it do, and what is it used for?

Like a lot of technical articles in Wikipedia, this one is unfortunately written for those who are already fairly knowledgeable or specialists in the field involved. I read the article and I have NO idea what the device does or what it is used for. I had a year of college physics, one and a half years of college chemistry, and college mathematics through spherical trigonometry and integral calculus, and with all that I still don't know what is going on. Keep in mind that you have teenage high school students who are just gaining knowledge about the physical world and how it works, make sure they can understand the basics, too. — Preceding unsigned comment added by Linstrum (talk • contribs) 02:07, 1 December 2012 (UTC)

According to the article the lens form[s] perfect geometrical images of two given concentric spheres onto each other - this could surely be expressed more clearly. As to applications, the article mentions microwave antennas, radar calibration standards and radar reflectors (with links in case the reader doesn't know what these things are) - can't see how that part could be any clearer. The article as it stands assumes the reader is familiar with the concepts of a lens and refractive index (only), so it ought to be comprehensible to teenagers. Perhaps you could re-read the page and identify what threw you the first time - then we could fix it. --catslash (talk) 03:04, 1 December 2012 (UTC)

I reorganized the article quite a bit. Please let us know if this helped.--Srleffler (talk) 06:51, 2 December 2012 (UTC)

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Sorry about getting back to you late, and sorry about this being so long.

The reorganization did help. Thanks for listening to my concerns, I appreciate it! I also appreciate how much work has been put into the article, and I am not finding fault with the article as a whole, just with the sequence of details that will ultimately help with more quickly understanding the basic Luneburg concept and real-world applications. I was referred to this article from another Wikipedia article where the functions, uses, types, real-world method of construction (like used at a "Luneburg lens factory"?), etc., of Luneburg lenses would have helped understand the original article, and where the Luneburg article addresses these was not easily found within a minute or two because of the method of fact presentation.

What I have to say below applies to problems I have with Wikipedia in general and I am not specifically singling out this article, it is one of a very great many that can be improved to make more understandable, at least from MY point of view (which I consider to be quite valid because of my ~ 50 years experience working in the various fields of the hard-core sciences). I used to edit scientific/technical papers and articles, and one of the problems I ran across fairly often was authors who confused the scientific or mechanical principals behind some kind of function (or how something is constructed) with explaining how it works in practical operation. The authors were quite knowledgable in their fields, but they were also really lousy fact-presenters - again, don't confuse having knowledge with having good writing, organizing, and presenting skills, they are not the same! In many cases, how something is used or its advantages are quite easily understood from its principles or construction, but not always. Like how those scientific principles are taken advantage of for its function or how those principles ultimately allow it to do what it does out there in the real world. As an example, one could describe a trout fishhook as "a small device typically constructed from a single piece of 0.75 millimeter tempered high carbon steel wire bent 180º in a 3.5 millimeter internal radius near one end with another 360º fully enclosed bend of 1 millimeter internal radius at the other end, with the tip end of the wire at the 180º bend acutely sharpened with a barb near its tip; the whole device being 15 millimeters in length" . Anyone lacking prior knowledge of what a fish is or a fish's basic behavior could never know from that description that the purpose of this device is for capturing-through-enticement small animals that live and feed in water, and is implemented by tying a long string to its "eye" end, that a small amount of some kind of food that a fish will enjoy eating is put on the hook to make the fish think the hook can be eaten so it will be taken into the mouth, the baited hook is placed in the fish's environment where the fish will detect it and take it into its mouth, that after the tip of the hook is in the fish's mouth the point and barb will usually penetrate the animal's strong mouth tissue to effectively attach the animal to the string so it can be put under control of the fisherman and taken out of the water, usually so the fish can be eaten. I do realize that it is beyond the scope of describing what a fishhook is to go into further detail about all kinds of fishing, but the basics of its operation are essential in describing what a fishhook is. The devil is in the details, and you surely have my sympathy about deciding how much information to give the reader to ensure a basic understanding of what is going on, especially when Wikipedia is also meant for young and unworldly people who may have only heard vague rumors that large bodies of water exist above ground and that catchable edible animals live in that water.

Okay, in the Luneburg Lens article, as one example, I would have put "Luneburg lenses are one type of gradient-index lens. They can be made for use with electromagnetic radiation from visible light to radio waves" as the very first sentence, not in the third paragraph where a reader may have started to lose incentive to keep reading because of finding what at first glance in his/her mind appears to be irrelevant "word salad" presented first. I would have written the first sentence as: "Luneburg lenses are one type of variable index lens, where the index of refraction changes, or gradates, from one part of the lens to another in a radially (spherically) symmetrical manner so that incoming rays originating at a point at infinity will all converge at one point not at infinity after passing through the lens. The gradient must start at a low index of refraction near the lens's outer perimeter and increase symmetrically toward its center for Luneburg lenses to function. See gradient-index lens. They can be made for use with electromagnetic radiation from visible light to radio waves."

If it applies (I don't know for sure if it does) I would have also added something like "The advantage of this kind of lens is a more efficient function or shape compared to conventional single index of refraction lenses" or some-such additional descriptors in your opening statement to help set the Luneburg lens apart from more traditional lens types. I am not sure, but from the article I kind of get the idea that the Luneburg lens is used for highly use-specific applications because the enormous difficulty in making a lens with a true index gradient, or even with concentric spheres with differing indices, is quite impractical compared to making single index of refraction lenses (I am quite aware of chromatic aberration and how color correction is addressed by using different indices of refraction in composite camera and binocular/telescope lenses). It seems that the Luneburg lens constructed from concentric spheres of differing indices could be considered a type of Fresnel lens, despite traditional Fresnel lenses having an incident angle gradient on one plane instead of an index gradient, but I didn't see any mention of the Fresnel principle in relation to stepped indices Luneburg lenses in the article. That gravitational lenses are Luneburg lenses is quite interesting, and obvious if one understands how the inverse square law works and that real world observable gravitational lenses are a phenomenon most often associated with large stars and dense galaxies where the distances involved are at a great enough scale for a gravitational gradient to be observable. That could be included in something like what kinds of indices are gradated that also work as Luneburg lenses, one doesn't normally think of gravity having a gradient here on the surface of the earth.

Like a said above, I do appreciate the work that has gone into presenting all the math/trig and getting the stuff correct, I have spent a good part of my life working with stuff like this, and I know this is not an easy subject to describe, hence the importance of making subjects like this as easy to assimilate by the "math and science novitiate" as possible. If they weren't "novitiates" they wouldn't be reading the article. We have to remember that Wikipedia is not a "washing-out" or "weeding-out" organization that separates the very-easily-educated from those who find it more difficult (like way, way too many colleges/universities promote), or that Wikipedia does not come with a professor to interpret difficult to understand articles. Unlike many college textbooks, Wikipedia articles have to stand on their own as far as being understandable without a teacher or numerous side trips to other Wikipedia pages or off-site articles to look up terms or related facts. Like I used to tell some of the authors who I edited for: "Don't force your readers to do YOUR work for you! When you do your work right it only has to be done once; but when you force your readers to do your work for you, that work has to be done over and over and over - - - ." — Preceding unsigned comment added by Linstrum (talk • contribs) 10:43, 26 December 2012 (UTC)

I restored the text that got deleted when you replied. This section was created by another editor to separate out the discussion you started from the earlier one above.

I agree with your line of thinking about how an article should be structured, and I think most experienced Wikipedia editors would as well. A good article starts by explaining the basics at a level aimed at a reader with no prior exposure to the subject. Technical details belong further down. This article is not very good, and could use some attention.

Badly-written articles arise because Wikipedia is written by volunteers—in fact by people just like you. You have some good ideas about how to change the introduction. Why don't you try adding them to the article? It works just like this talk page: you click "edit" at the top of the article page and make whatever changes you think are needed. Other editors will tinker with your text too—you'll probably find that some of what you write gets deleted and some gets kept. This is a normal part of the Wikipedia process. When it works well, it can become a real collaboration with different editors trying different phrasings until the best one is found. In the best cases, we end up with something that is better than any one of us could do on our own. I added a boilerplate "welcome" message to your personal talk page. It has some useful links to information about how Wikipedia works.--Srleffler (talk) 18:17, 26 December 2012 (UTC)

Should this article be the redirect for Dielectric lens?

The term Dielectric lens redirects to this article. Dielectric lenses are lenses used to focus radio waves or microwaves instead of light, and are used in microwave antennas. There are many types, the Luneburg lens is just one of them. Dielectric lenses are not covered adequately by this article. so I don't think this article should be the target for that term. Is there a better target for it, or should a new Dielectric lenses article be written? --Chetvorno^TALK 06:01, 21 August 2017 (UTC)

Redirects are often used as placeholders for articles that have not yet been created. Feel free to change Dielectric lens into an actual article, if you know enough about them to get it started. Don't create Dielectric lenses: article names are supposed to be singular, not plural.--Srleffler (talk) 06:16, 21 August 2017 (UTC)

Metal grill lens of radar antenna for US Nike Ajax antiaircraft missile, 1960s.

Thanks. I think I'll talk to some other editors of electronic articles before creating the article, to see what new articles they think we need in this area. In addition to dielectric lenses there are also several other types of lens antennas, none of which are currently covered in WP. Maybe it would be better to have a Lens antenna article to cover all these types. --Chetvorno^TALK 22:46, 2 September 2017 (UTC)