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"

$\frac{1}{S_1} + \frac{1}{S_2} = \frac{1}{f}$ is listed as the Gaussian Lens Formula in my copy of Hecht [1], 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

This article is a mess. It's unsuitable for most beginning readers, and is a tiresome repetition of advanced information that would already be understood by people with advanced coursework.

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
${P} = \frac{1}{f} = (n-1) \left[ \frac{1}{R_1} - \frac{1}{R_2} + \frac{(n-1)d}{n R_1 R_2} \right],$
which I believe is good even for thick lenses. The usual thin-lens approximation for the lensmaker's equation is
${P} = \frac{1}{f} = (n-1) \left[ \frac{1}{R_1} - \frac{1}{R_2} \right].$
--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:
${EFL(sphere)} = \frac{1}{2} \frac{n}{(n-1)}R.$
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:
${P} = \frac{1}{f} = (n-1) \frac{2}{R} (2-n),$
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)
• ^ Hecht, Optics, 4th edition, 2002, pg. 158