# Talk:Lens (optics)

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## Lens grinding

Isaac Asimov said, “I don’t understand the ecstasy of lens grinding myself, but the history of astronomy is littered with peculiar people who would rather grind lenses than eat.” (Source: “Quasar, Quasar, Burning Bright”, by Isaac Asimov. Doubleday, 1978, p. 196.)

Asimov identifies Alvan Graham Clark as the first notable American lens grinder in a field then dominated by British, French, and German practitioners. However, there doesn’t seem to be any articles in Wikipedia on lens grinding. As far as I can tell, it is only discussed in the article on Baruch Spinoza. Would it fit into the history section here? Psalm 119:105 (talk) 10:46, 24 January 2011 (UTC)

Another possibility would be Fabrication and testing of optical components.--Srleffler (talk) 05:16, 25 January 2011 (UTC)

## Misnamed Formula in "Imaging Properties"

${\displaystyle {\frac {1}{S_{1}}}+{\frac {1}{S_{2}}}={\frac {1}{f}}}$ is listed as the Gaussian Lens Formula in my copy of Hecht (Hecht, Optics, 4th edition, 2002, pg. 158), not the thin lens formula. --97.83.155.54 (talk) 10:58, 28 March 2011 (UTC)

The formula has more than one name.--Srleffler (talk) 23:55, 28 March 2011 (UTC)

## Mistake regarding Archimedes' "burning glass"

It is stated in the article that Archimedes used a "burning glass" which was a biconvex lens. However, most sources state that what was actually used was a series of plane mirrors. A biconvex lens of the scale necessary to burn a hole in a wooden ship would be incredibly difficult to produce in 424 BC, whereas modern replications of the "burning mirror" method have yielded results.

69.110.229.37 (talk) 05:53, 9 June 2011 (UTC) Curtis

Archimedes isn't mentioned in this article. I think you mean over in Burning glass.

## "History"

The "History" section stops at John Dollond in 1758. Obviously there is more that needs to be added. Fountains of Bryn Mawr (talk) 21:50, 8 March 2012 (UTC)

There is a main history article. Why not use this? Tagremover (talk) 21:56, 8 March 2012 (UTC)
Additionally camera lens covers a LOT. Tagremover (talk) 21:58, 8 March 2012 (UTC)
We certainly can use the main history article, but this article's history section should contain a good, concise summary of the full history article. (See WP:Summary style.) The history of optics doesn't stop in 1758, and neither should the history section here.--Srleffler (talk) 03:52, 15 March 2012 (UTC)

## An example of an almost completely useless wiki article

And how many readers will be interested in someone's 600 word shaky historical speculations, following the brief, banal opening?

It's an example of how "committee decisions" of "editors" can be worse than useless, in that they alienate most readers from understanding. The Britiannica does a far better job at describing the topic. This Wikipedia at its most pointless. Except, of course, lengthy articles about pop stars citing fashion magazines. 76.102.1.193 (talk) 05:32, 25 August 2012 (UTC)

Thank you for your suggestion. When you believe an article needs improvement, please feel free to make those changes. Wikipedia is a wiki, so anyone can edit almost any article by simply following the edit this page link at the top.
The Wikipedia community encourages you to be bold in updating pages. Don't worry too much about making honest mistakes—they're likely to be found and corrected quickly. If you're not sure how editing works, check out how to edit a page, or use the sandbox to try out your editing skills. New contributors are always welcome. You don't even need to log in (although there are many reasons why you might want to).--Srleffler (talk) 19:56, 25 August 2012 (UTC)

## Mobile/small-screen fix needed

The side-by-side diagrams and photos in Lens (optics)#Types of simple lenses are too wide in their tables to fit on mobile devices (typically 320px wide). These should be tweaked so they passively degrade to one-over-the-other on narrow screens; if nobody gets to it, this is a note to myself to poke at it later. :) --brion (talk) 19:15, 24 September 2012 (UTC)

## no derivation for the lensmaker's equation?

It just appears out of nowhere. Can someone provide the derivation for it? 137.54.11.202 (talk) 05:54, 2 October 2012 (UTC)

The equation is given without derivation because Wikipedia is not a textbook. Derivations of equations are (often) out of our scope. This question is best handled at the Science Reference Desk (where you have already asked it).--Srleffler (talk) 03:57, 3 October 2012 (UTC)

## notes/ remarks on lensmaker's equation

After some effort to try to derive the lensmaker's equation I discovered that it is an approximation, be it a very good one under normal circumstances. The approximation used is that d << R1,R2. I recommend that this be included in the description of this variable (d).Gerald Tros (talk) 23:56, 29 December 2012 (UTC)

Are you sure the form given in this article has that approximation? The form given here is
${\displaystyle {P}={\frac {1}{f}}=(n-1)\left[{\frac {1}{R_{1}}}-{\frac {1}{R_{2}}}+{\frac {(n-1)d}{nR_{1}R_{2}}}\right],}$
which I believe is good even for thick lenses. The usual thin-lens approximation for the lensmaker's equation is
${\displaystyle {P}={\frac {1}{f}}=(n-1)\left[{\frac {1}{R_{1}}}-{\frac {1}{R_{2}}}\right].}$
--Srleffler (talk) 22:52, 30 December 2012 (UTC)
Yes, Srleffler, I'm fairly sure of it. I stumbled upon this topic while working out the focal length of a pretty thick lens, a sphere (my girlfriend's 95 mm diameter "crystal ball", at home, just doing some physics for fun). My result was consistent with web searches, which was:
${\displaystyle {EFL(sphere)}={\frac {1}{2}}{\frac {n}{(n-1)}}R.}$
In this case (the sphere), the thickness d = 2R. I came across your lensmaker's equation and tested it with d = 2R and R1 = R2 = R. It didn't become EFL(sphere). So I did the nitty gritty for any thickness d and I eventually succeeded in producing the lensmaker's equation by dropping terms in d^2.
I've been through it only once, thoroughly. Wouldn't publish it yet, as such. I was hoping it might ring a bell with someone else.
I now suspect that the term "thin lens approximation" should be read as "the ideally thin lens approximation" (i.e. assuming d = 0, or very close to 0). I further suspect that the lensmaker's equation accurately caters for lenses of thickness up to several mm. Anyway :-) Gerald Tros (talk) 21:30, 1 January 2013 (UTC)
You didn't follow the sign convention. For a ball lens, R2 = –R. If you substitute into the first expression I gave (which is the one given in this article), you get your expression for the EFL.--Srleffler (talk) 23:36, 1 January 2013 (UTC)
Ah, I'm sorry, I'm afraid I reported incorrectly. I did in fact use R1 = R and R2 = –R (and d=2R). What I get then is:
${\displaystyle {P}={\frac {1}{f}}=(n-1){\frac {2}{R}}(2-n),}$
which is not the EFL(sphere). Would you like to try this for yourself? I reiterate my observation that I had to drop terms in d^2 during derivation to get from an exact expression to the lensmaker's equation (everything done in the paraxial approximation, of course). Now d=2R is a really big d :-) Gerald Tros (talk) 00:35, 2 January 2013 (UTC)
You made a math error somewhere. The equation you give is not what results from substituting those variables into the lensmaker's equation. I have done the math and it comes out to the correct expression for the EFL.--Srleffler (talk) 02:52, 3 January 2013 (UTC)
Thank you for taking the trouble. And ah, yes, I've found my (elementary!?!) mistake, I forgot the "n" in the denominator (the n in in nR1R2). I now agree with your check. I offer you my humble apologies. Your check confirms that the LMEq holds perfectly for this particular spherical lens, a pretty damn thick lens. I'll now go back and review my "dropping terms in d^2" calculations, expecting that something be awry there too... So chances are good we're all square, I reckon. Thank you for your trouble.--Gerald Tros (talk) 02:17, 4 January 2013 (UTC)

## "simple glass meniscal lenses", 8th Century or 5th?

This article refers to "simple glass meniscal lenses", and gives a date of the 8th Century. This disagrees with 5th Century in the Glasses article. Which is correct? I added [citation needed] to both articles. The other article was uncited. I don't know if the reference here can be looked up or if it includes that information. Thanks! Misty MH (talk) 08:08, 25 July 2013 (UTC)

I changed the tag here to "verify source", since the issue is not that a citation is needed, but rather that we need someone to go look up the cited source and verify that it says what is claimed.--Srleffler (talk) 03:50, 26 July 2013 (UTC)

## Need reference for "thin lens formula"

Hi - I write for Wikiversity mostly, and am trying to bridge the gap between the completeness of many Wikipedia articles and the needs of first and second year college students. I assigned a lab in which the students are asked to verify that this is called the "thin lens formula" after seeing that this name for the formula is omitted on the article Thin lens. Some of my students are beginning to edit, and they will correct this on Thin lens.--Guy vandegrift (talk) 15:57, 16 March 2015 (UTC)

## Illustration of negative meniscus lens is not clear

The lens looks like it is evenly thick and would have little or no negative character. It would be better with an illustration where the negative meniscus was clearly thinner in the middle. Jeff tupo (talk) 11:59, 21 April 2015 (UTC)

Done --Guy vandegrift (talk) 13:11, 21 April 2015 (UTC)

## Language consistence

Article is currently written in a mixture of different forms of English, against WP:ARTCON. (For example, both centre and center are used in the article, and there are more such examples). Usually, the guideline would be to go back to the original language form used. That would be British English, by the way. However, I'll readily acknowledge that's almost 13 years ago and the article has changed significantly since then, so instead of going boldly ahead, I'm asking here first if anyone has a problem with me bringing the article back into line with British English. Alternatively, if someone has a good reason for this article to use a different variation of English (such as American English) to be used that I have overlooked, please let me know. AddWittyNameHere (talk) 22:36, 1 June 2015 (UTC)

By means of the lack of response here, I am tentatively concluding there are no issues if I were to bring this article's language consistency back in line to British English. If there still has been no response in 36-48 hours, I likely will go ahead and just simply fix it. AddWittyNameHere (talk) 04:13, 6 June 2015 (UTC)
Go for it. It's the right thing to do.--Srleffler (talk) 17:25, 6 June 2015 (UTC)

## Requested move 12 August 2015

The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section.

The result of the move request was: not moved. Jenks24 (talk) 11:37, 20 August 2015 (UTC)

– The concept in optics seems to be the primary topic by long-term importance. bd2412 T 14:31, 12 August 2015 (UTC)

• Yep, GregKaye 20:05, 12 August 2015 (UTC)
• Oppose, unless the plan is to convert the optics article into more of a broad-concept article. For example, someone looking up "lens" could honestly be trying to look up one of the sub articles listed on the disambiguation page under "Lens (optics)". (It already looks like sort of a braid concept article, but I'm thinking a list needs to be added somewhere to provide brief explanations of manufactured optic lens types.) Steel1943 (talk) 19:04, 13 August 2015 (UTC)
• What about lens (anatomy)?  AjaxSmack  01:43, 15 August 2015 (UTC)
Isn't a lens in anatomy merely a Lens (optics) that happens to be part of an animal? bd2412 T 16:50, 15 August 2015 (UTC)
True but irrelevant since anatomical lenses are not covered in the lens (optics) article. Lens (anatomy), camera lens and corrective lens are all significant topics also referred to simply as "lens" (unlike contact lens which usually isn't). I'm not convinced that the great majority of readers are seeking the optical lens article rather than one of those other three articles even if they are all technically optical lenses. Therefore,...
• ...Oppose per User:Steel1943 but am more sk/ceptical of the need for a broad-concept article. —  AjaxSmack  17:11, 16 August 2015 (UTC)
• Opppose. Lens (optics) is clearly not primary over Lens (anatomy) and Camera lens by usage. While one might argue that the optics article is more fundamental, there is greater practical benefit in having Lens be a dab page, so that when "lens" is used ambiguously in articles about biology or cameras, the incorrect links can be found and corrected. If you move Lens (optics) to "Lens", many incorrect links will be created, and fixing them will be more difficult.--Srleffler (talk) 06:15, 17 August 2015 (UTC)
• Oppose. Not convinced it's the primary topic over lens (anatomy) and other pages of the same name. Calidum 03:27, 20 August 2015 (UTC)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

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## Inverted cone lens?

Could one of our resident optics gurus add a paragraph or two about inverted cone lenses? [1][2] Thanks! --Guy Macon (talk) 09:02, 8 March 2016 (UTC)

They aren't lenses; they are reflectors.--Srleffler (talk) 05:23, 9 March 2016 (UTC)
The optical structures around light sources are sometimes called lenses. These inverted cones are molded plastic that work by total internal reflection, converting the upward beam of the LED to a horizontal ring, with vertical spread corresponding to the original beam width. Not related to lenses that affect focus, which is what this article is about. Dicklyon (talk) 05:26, 9 March 2016 (UTC)