Talk:Lens

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 (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

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

${P}={\frac {1}{f}}=(n-1)\left[{\frac {1}{R_{1}}}-{\frac {1}{R_{2}}}+{\frac {(n-1)d}{nR_{1}R_{2}}}\right],$

which I believe is good even for thick lenses. The usual thin-lens approximation for the lensmaker's equation is

${P}={\frac {1}{f}}=(n-1)\left[{\frac {1}{R_{1}}}-{\frac {1}{R_{2}}}\right].$

--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 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)

---

• Lens (optics) → Lens
• Lens → Lens (disambiguation)

– 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)

  @AjaxSmack: 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.

External links modified

Hello fellow Wikipedians,

I have just added archive links to one external link on Lens (optics). Please take a moment to review my edit. If necessary, add {{cbignore}} after the link to keep me from modifying it. Alternatively, you can add {{nobots|deny=InternetArchiveBot}} to keep me off the page altogether. I made the following changes:

• Added archive https://web.archive.org/20091123101108/http://www.optics.arizona.edu:80/OPTI696/2005/axicon_Proteep.pdf to http://www.optics.arizona.edu/OPTI696/2005/axicon_Proteep.pdf

When you have finished reviewing my changes, please set the checked parameter below to true to let others know.

Y An editor has reviewed this edit and fixed any errors that were found.

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers. —^{cyberbot II}_{Talk to my owner:Online} 00:49, 16 October 2015 (UTC)

External links modified

Hello fellow Wikipedians,

I have just added archive links to 3 external links on Lens (optics). Please take a moment to review my edit. If necessary, add {{cbignore}} after the link to keep me from modifying it. Alternatively, you can add {{nobots|deny=InternetArchiveBot}} to keep me off the page altogether. I made the following changes:

• Added archive http://web.archive.org/web/20140908111903/http://cmip.pratt.duke.edu/tomuri2009/sites/cmip.pratt.duke.edu.tomuri2009/files/pubs_purdue/2010_APB_MDC_Superlensing.pdf to http://cmip.pratt.duke.edu/tomuri2009/sites/cmip.pratt.duke.edu.tomuri2009/files/pubs_purdue/2010_APB_MDC_Superlensing.pdf
• Added archive http://web.archive.org/web/20160101061317/http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20070301.shtml to http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20070301.shtml
• Added archive http://web.archive.org/web/20151016004906/http://www3.usal.es/%7Ehistologia/aplicacion/english/museum/microsco/micros01/micros01.htm to http://www3.usal.es/%7Ehistologia/aplicacion/english/museum/microsco/micros01/micros01.htm

When you have finished reviewing my changes, please set the checked parameter below to true to let others know.

Y An editor has reviewed this edit and fixed any errors that were found.

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—^{cyberbot II}_{Talk to my owner:Online} 11:32, 27 February 2016 (UTC)

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)

Possessive apostrophes

User:Srleffler, please do not revert edits without giving an edit summary, particularly whe the edit you are reverting did leave a summary.

The issue in question is a grammatical dispute over which form of the possessive to use with a name ending in an s. Should we have:

• Aristophanes' play The Clouds

or

• Aristophanes's play The Clouds

Until recently we had Aristophanes'. An IP editor changed it to Aristophanes's with the edit summary "Fixed grammar". I reverted this with the edit summary " was not incorrect, see MOS:POSS, based in pronounciation". Srleffler has re-reverted, without an edit summary.

The guidance in the Wikpedia Manual of Style is at MOS:POSS. This says that there are two accepted styles when forming the possessive of a singular noun ending with one s. One style is to always add 's, the other style is to either add just an apostrophe or to add 's, depending on pronunciation. I favour the second style. It is unclear whether Srleffler favours the first style or if he or she would pronounce this differently.

When using the pronounciation-based style, writing Aristophanes's play implies that it is pronounced "Aris-to-fa-nees-es play". I would say "Aris-to-fa-nees play", so I would write Aristophanes' play. However, I would write "keeping up with the Jones's".

I am not attempting to impose my style on Wikipedia, but to resist "grammatical corrections" of things that are not incorrect. I will re-revert. Verbcatcher (talk) 02:07, 4 June 2017 (UTC)

Sorry about that. I'm not sure how I ended up reverting you. I agree with you. --Srleffler (talk) 19:26, 4 June 2017 (UTC)

External links modified

Hello fellow Wikipedians,

I have just modified one external link on Lens (optics). Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

• Added archive https://web.archive.org/web/20160304054022/http://www.digitalartform.com/lenses.htm to http://www.digitalartform.com/lenses.htm

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

This message was posted before February 2018. After February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete these "External links modified" talk page sections if they want to de-clutter talk pages, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{source check}} (last update: 5 June 2024).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot (Report bug) 14:36, 2 August 2017 (UTC)

Rare case?

"In the extreme case where an object is an infinite distance away, S1 = ∞, S2 = f and M = −f/∞= 0, indicating that the object would be imaged to a single point in the focal plane. In fact, the diameter of the projected spot is not actually zero, since diffraction places a lower limit on the size of the point spread function. This is called the diffraction limit."

There is a limit, but it is not zero. Right. I think this needs to be rewritten. It is certainly not an "extreme case" to not be able to see objects until you approach them... Try looking out in your garden and see if you can see the insects until you approach them or if you don't have a garden place something that doesnt diffract too much on the ground in a parking garage and see if you can see it as you move away from it... It is really true. Things disappear with distance. It's amazing i know. — Preceding unsigned comment added by 80.212.223.246 (talk) 09:36, 14 June 2018 (UTC)

The case described is extreme, in the sense that infinity is by its nature extreme. You do not in fact encounter this case looking at objects in your garden—even quite distant objects are a finite distance away, and have a nonzero magnification.

Those sentences are not really talking about the fact that things get harder to see with distance, but rather the fact that physical optics departs from the naive predictions of geometric optics when objects are very far away. You don't need to consider that to understand why objects disappear when they are too far away. Your eye has a finite resolution, even if considered using geometric optics. --Srleffler (talk) 04:54, 15 June 2018 (UTC)

Requested move 22 July 2019

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 after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: consensus against this proposed move. DrKay (talk) 18:55, 8 August 2019 (UTC)

---

Lens (optics) → Optical lens – Natural disambiguation is preferred over parenthetical disambiguation. Interstellarity (talk) 18:36, 22 July 2019 (UTC)

• Oppose Since the first word most people will type in is likely going to be "Lens". However, I support moving this article to Lens as the WP:BROADCONCEPT and moving Lens to Lens (disambiguation)._{ZXCVBNM (TALK)} 23:37, 22 July 2019 (UTC)
• Oppose. Nobody calls it an "optical lens". It's just a lens. I also oppose the move suggested by ZXCVBNM, which has been discussed before.--Srleffler (talk) 00:26, 23 July 2019 (UTC)
• Support move to Lens as proposed above. Rreagan007 (talk) 01:07, 23 July 2019 (UTC)
  • If so, then the existing Lens better go to Lens (disambiguation). Anthony Appleyard (talk) 04:51, 23 July 2019 (UTC)
• Speedy close and re-list, moving to Lens Red Slash 15:18, 23 July 2019 (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.

Requested move 8 August 2019

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 after discussing it on the closer's talk page. No further edits should be made to this discussion.

The result of the move request was: Moved. This is the primary topic and a Broad-concept article.(non-admin closure) Cwmhiraeth (talk) 10:23, 21 August 2019 (UTC)

---

• Lens (optics) → Lens
• Lens → Lens (disambiguation)

– Some support for this move in the requested move discussion of 22 July 2019, opening for re-listed discussion. DrKay (talk) 18:55, 8 August 2019 (UTC)

• Support per WP:BROADCONCEPT. Rreagan007 (talk) 00:38, 9 August 2019 (UTC)
• Support as obvious primary topic by criterion 2. Rescoping into broad concept isn't a bad idea but I think it has primacy anyways. Red Slash 02:03, 9 August 2019 (UTC)
• Oppose. WP:BROADCONCEPT doesn't apply. The term has too many uses that are not related to optical lenses. Having Lens be this article will create too many bad links, that were intended for other lens articles.--Srleffler (talk) 02:58, 9 August 2019 (UTC)
• Oppose – the term is too ambiguous to be doing a primarytopic grab. The current disambig page looks great for this. Dicklyon (talk) 03:08, 9 August 2019 (UTC)
• Oppose. Lens (optics) is not a broad-concept article. Lens (anatomy) and the others might be subtopics but they are prominent, historically significant articles in their own right and potential search/link targets. Links to them should not be hidden within a huge article. Not to mention Lens, Pas-de-Calais and RC Lens. —Xezbeth (talk) 09:16, 9 August 2019 (UTC)
• Support - I haven't checked, but I'll bet that the pageviews of optical lenses (including special cases) is much greater than all others put together. If you "buy" a lens it is almost surely a refractive lens. Other uses are usually names given based on the previous concept of optical lenses and will be understood as such by the reader. Interferometrist (talk) 19:23, 12 August 2019 (UTC)
• Support per WP:BROADCONCEPT, and per the above. bd2412 T 13:25, 17 August 2019 (UTC)
• Support. Hard to argue that this is not the primary topic. A hugely encyclopedic topic, and other uses are either specialised cases of it (making it broad concept), or are much lower in page-views/significance. No denying Lens in France and its football club are a relatively prominent topics, but not as much as the optical lens.  — Amakuru (talk) 18:39, 17 August 2019 (UTC)
• Oppose this move 2601:541:4500:1760:5C04:6A81:78FE:E352 (talk) 19:37, 19 August 2019 (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.

dobsonian lens

what is the correct distances and adjusting to be able create your own properly ?

This isn't really the right place to ask that kind of question. Wikipedia talk pages are dedicated to discussions related to how to improve the article. Wikipedia is not a "how-to" guide. Also, the general article on lenses is not the right place to look for information on a very specific type of lens.

You might be interested in the article Dobsonian telescope.--Srleffler (talk) 02:48, 27 October 2019 (UTC)

Science

Uses of lenses 182.182.71.136 (talk) 19:43, 27 April 2022 (UTC)

Need liquid lens info

As above 12.199.163.10 (talk) 17:17, 8 June 2022 (UTC)

Angular Magnification

I was looking for the formula that would give the ratio of angle of incoming rays to angle of outgoing rays, and in particular I'm interested in the case where the object being imaged is at an extreme distance (e.g. astronomical). I would consider this to be "magnification", although I understand the definition of magnification given in the article. There are basically two kinds of magnification when talking about lenses, spatial and angular magnification. I believe when talking about a telescope's magnification, we would be talking about angular magnification? Tedwtoal (talk) 21:52, 4 August 2022 (UTC)

There are several kinds of magnification. See Magnification for more on the topic, including angular magnification.--Srleffler (talk) 17:35, 7 August 2022 (UTC)

Image size at focal plane

I wanted to be able to calculate the size (e.g. in meters) of the image at the focal plane. I think I understand how, but it might be good to explicitly show a formula. I am particularly interested in images of objects at astronomical distances. What I THINK is the formula is: say we are talking about imaging a planet at distance D with diameter d in a telescope with focal length f where f << D; then the image size would be d times the magnification, or df/D (?). Tedwtoal (talk) 21:57, 4 August 2022 (UTC)

Yes, if the planet is not too far away. If you're imaging a distant star or a planet around one, geometrical optics fails; the image size is limited by diffraction. When astronomers photograph stars, I don't believe the size of the spots on the film has any relation to the size of the star; it's entirely determined by the diffraction of the telescope and aberrations in our atmosphere. Astronomers look at the brightness of the spots and their spectrum, not their size.--Srleffler (talk) 17:57, 7 August 2022 (UTC)

The correct possessive form of lens: lens's or lens'?

Both are currently used in this article. 206.180.44.25 (talk) 14:15, 22 April 2024 (UTC)

Non spherical types

In this section there is a mistake. Near the top is a piece about the costs of making them. But there exists a type of non spherical lens that is even easier to make than a spherical one. You hold a metallic plane with a hole in the centre horizontally and drop liquid glass into the hole. After cooling you have a very good lens. Unfortunately I don't have a reference for this, but I know there must be one, because I read it many years ago (on paper). 176.0.164.84 (talk) 11:23, 7 October 2024 (UTC)