text:
Talk:Veterans Day

Wiki Education Foundation-supported course assignment
This article was the subject of a Wiki Education Foundation-supported course assignment, between 12 January 2021 and 30 April 2021. Further details are available on the course page. Student editor(s): StudiousBear23, Shelbyfulton, Laurel Genova, Ellemahoney12.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 12:20, 17 January 2022 (UTC)

Edit Request: Irrelevant and Opinionated Segment
While I do not oppose the idea of a ferdural holiday for elections, I do oppose the placing of a political talking point in an article about Veterans Day.

"Several commentators have noted the irony of Election Day being a regular working day, while Veterans Day, which typically falls the following week, is a federal holiday. Many people have called for the holidays to be merged, so citizens can have a day off to vote. This would be seen as a way to honor voting by exercising democratic rights.[9][10]"

This segment and its citations should be removed as it has nothing to do with the observation of Veterans Day nor does it have any direct relevance for the holiday itself other than an unstated and undefined reference to "soldiers dying for the right to vote". — Preceding unsigned comment added by 210.172.200.126 (talk) 00:09, 14 November 2016 (UTC) I LIKE POTATOES!!!!!!!!!!!!!!!!!!

 * ok.? 2601:603:A7F:B110:C55A:DCCB:A597:269B (talk) 13:09, 26 October 2023 (UTC)

I COMPLETELY agree. Why bring it up in an article describing Veterans Day? Because they are both in November? It honestly seems like it was inserted because someone has an agenda about making election day a holiday and for no other relevant reason. Create, or edit and existing page, about making election day about holiday. Please, somebody edit this by removing this political insert. This is supposed to be an encyclopedia article on Veterans Day. I guaruntee you won't see this point being made in the Encyclopedia Britannica article on Veteran's Day (if there is such an article) because it is simply not appropriate here.173.244.48.78 (talk) 10:58, 30 May 2017 (UTC)

In addition, I believe it is incorrect. It makes no sense to "honor voting". If this were to make any sense it would say "honor veterans". However, that is moot if this is removed which I agree it should be.

No Mention of Attributive
The article states: the United States Department of Veterans Affairs Web site states that the attributive (no apostrophe) rather than the possessive case is the official spelling..."

The DVA website says nothing at all about attribute case -- there is no such case, for a start.

The case is called 'genitive' and it includes both possession and attribution.

The DVA website states only that the holiday is called Veterans Day instead of Veteran's Day or Veterans' Day because the day does not belong to Veterans.

In fact, the Act of Congress that renamed Armistice Day actually renamed it *All* Veterans Day. We later dropped the 'All' part.

But there is absolutely nothing on the website about the spelling being attributive rather than possessive. So the material about it being attributive should be removed. 73.162.218.153 (talk) 22:53, 12 November 2016 (UTC)

Semi-protected edit request on 11 November 2014
The National Veterans Award was also created in 1954. Congressman Rees of Kansas recieved the first National Veterans Award in Birmingham, Alabama for his support offering legislation to make Veterans Day a federal holiday.

RevRobtheRR (talk) 20:33, 11 November 2014 (UTC)

That's it! Received is the correct spelling...
 * Yes check.svg Done Cannolis (talk) 20:49, 11 November 2014 (UTC)

Idea that Wilson declared a first Armistice Day in November 1919 "proclamation" is mostly a myth.
According to a New York Times article published on 8 November 1919 entitled "President Prepares a message to the People for Armistice Day", "President Wilson today wrote a message to the American People which will be made public on Armistice Day, Nov. 11." Other contemporaneous and official sources call this same statement a "greeting" or an "address". Even though Wilson routinely issued "proclamations", this was not one of them.

See: http://aveteransday.com — Preceding unsigned comment added by Rdritik (talk • contribs) 07:12, 6 October 2018 (UTC) http://query.nytimes.com/mem/archive-free/pdf?res=9A0CE2DC123FE432A2575BC0A9679D946896D6CF

https://news.google.com/newspapers?nid=2209&dat=19191011&id=XRVAAAAAIBAJ&sjid=XaQMAAAAIBAJ&pg=7270,2198280&hl=en

https://books.google.com/books?id=WYg_AQAAMAAJ&pg=PA8803&lpg=PA8803&dq=%22a+year+ago+today+our+enemies+laid+down+their+arms%22&source=bl&ots=SAyvxEs4yr&sig=tkkBHzQnk_V0Cnessu7W0Xyl6Ag&hl=en&sa=X&ved=0CCEQ6AEwAWoVChMIrYvdjcOJyQIViHgmCh1ytwxt#v=onepage&q=%22a%20year%20ago%20today%20our%20enemies%20laid%20down%20their%20arms%22&f=false

Compare the "Mother's Day" Proclamation of 1914 and its unambiguous formality and intent: http://www.archives.gov/historical-docs/todays-doc/?dod-date=509

Obviously, one way or another, the notion of "Armistice Day" was already well-established before the Wilson's message, since the message itself and the pre-message press refer to it simply and casually as "Armistice Day". Furthermore his "message" or "address" was not only not a formal proclamation but it did not in any way "declare" or propose to create any holiday or new day of remembrance but simply speaks about the one year anniversary of the cessation of hostilities and what the occasion already known as "Armistice Day" means to Americas. The full test of the address demonstrates this:

"ADDRESS TO FELLOW-COUNTRYMEN    The White House, November 11, 1919.   A year ago today our enemies laid down their arms in accordance with an armistice which rendered them impotent to renew hostilities, and gave to the world an assured opportunity to reconstruct its shattered order and to work out in peace a new and juster set of inter national relations. The soldiers and people of the European Allies had fought and endured for more than four years to uphold the barrier of civilization against the aggressions of armed force. We ourselves had been in the conflict something more than a year and a half. - With splendid forgetfulness of mere personal concerns, we re modeled our industries, concentrated our financial resources, increased our agricultural output, and assembled a great army, so that at the last our power was a decisive factor in the victory. We were able to bring the vast resources, material and moral, of a great and free people to the assistance of our associates in Europe who had suffered and sacrificed without limit in the cause for which we fought. Out of this victory there arose new possibilities of political freedom and economic concert. The war showed us the strength of great nations acting together for high purposes, and the victory of arms foretells the enduring conquests which can be made in peace when nations act justly and in furtherance of the common interests of men. To us in America the reflections of Armistice Day will be filled with - solemn pride in the heroism of those who died in the country’s service, and with gratitude for the victory, both because of the thing from which it has freed us and because of the opportunity it has given America to show her sympathy with peace and justice in the councils of nations. WOODROW WILSON."

Thus the purported "Proclamation" of Armistice Day by Wilson in 1919 is essentially a myth.

00:03, 12 November 2015 (UTC) — Preceding unsigned comment added by Criticality (talk • contribs)

Semi-protected edit request on 11 November 2016
The caption on the photo in the main infobox at the top-right of the article currently reads: " Joseph F. Ambrose, an 86-year-old World War I veteran, attends the dedication day parade for the Vietnam Veterans Memorial in 1982, holding the flag that covered the casket of his son, who was killed in the Korean War. "

Since Joseph F. Ambrose's Wikipedia page and this source linked to from his Wikipedia page say that he died in 1988, the caption can be misinterpreted to mean that he is currently 86-years-old. Note his date of birth here.

I propose changing the caption to the following: " Joseph F. Ambrose, a World War I veteran, attends the dedication day parade for the Vietnam Veterans Memorial in 1982 at 86 years old, holding the flag that covered the casket of his son, who was killed in the Korean War. "

Deleting any information about his age in this caption would also work.

I apologise for any mistakes I may have made; I'm new to editing (obviously).

Blueinkblink (talk) 02:40, 11 November 2016 (UTC)

 * ✅  Paine   u/ c  06:21, 11 November 2016 (UTC)

Semi-protected edit request on 14 November 2016
In the article there is a mistake made in the year that Veterans Day was first celebrated it says the year 1918 but it is the year of 1919.

Sophisticatednyny (talk) 21:36, 14 November 2016 (UTC)
 * Red information icon with gradient background.svg Not done: Where does it say that? It says 1919 due to the war ending in 1918. 🔯 Sir Joseph 🍸 (talk)  16:17, 15 November 2016 (UTC)

[United States Statutes at Large, Volume 117, 108th Congress, 1st Session] [From the U.S. Government Printing Office, www.gpo.gov]

EMPORIA, KANSAS--FOUNDING CITY OF VETERANS DAY <>

Whereas in 1953, Alvin J. King of Emporia, Kansas, proposed that Armistice Day be changed to Veterans Day to recognize and honor all veterans from all wars and conflicts;

Whereas in 1953, Veterans Day was first organized and celebrated in Emporia, Kansas;

Whereas although Alvin King was only 15 years old when the United States went to war in 1917 and never served in the Armed Forces, he had a deep respect for veterans;

Whereas Alvin King's stepson, John Cooper, whom he had raised, was killed in action in Belgium during World War II while serving with Rifle Company B, 137th Infantry Regiment;

Whereas after World War II, Alvin King developed friendships with the surviving members of Rifle Company B, 137th Infantry Regiment;

Page 2959 117 STAT. 2959

Whereas in the early 1950s, Alvin King suggested either creating a special day to honor all veterans or adapting Armistice Day so that it was dedicated to all veterans since, at that time, Armistice Day honored the veterans of World War I;

Whereas by 1953, the community of Emporia, Kansas, had raised enough money to send Alvin King and his wife, Gertrude, to Washington, D.C. to garner support for an official veterans day;

Whereas Alvin King had a friend and supporter in Representative Ed Rees of Emporia, Kansas, who was strongly in favor of King's idea and said ``it would give the holiday a new meaning and more widespread patriotic observance'';

Whereas on June 1, 1954, President Dwight D. Eisenhower, who was raised in Kansas, signed into law the Act proclaiming November 11 as Veterans Day (Public Law 380 of the 83rd Congress);

Whereas on October 8, 1954, President Eisenhower issued a presidential proclamation concerning Veterans Day in 1954 in which he stated, ``On that day let us solemnly remember the sacrifices of all those who fought so valiantly, on the seas, in the air, and on foreign shores, to preserve our heritage of freedom, and let us reconsecrate ourselves to the task of promoting an enduring peace so that their efforts shall not have been in vain''; and

Whereas the first nationwide observance of Veterans Day was on November 11, 1954: Now, therefore, be it

Resolved by the House of Representatives (the Senate concurring), That Congress hereby-- (1) encourages Americans to demonstrate their support for veterans on Veterans Day by treating that day as a special day of remembrance; (2) declares Emporia, Kansas, to be the founding city of Veterans Day; (3) recognizes Alvin J. King, of Emporia, Kansas, as the founder of Veterans Day; and (4) recognizes that Representative Ed Rees, of Emporia, Kansas, was instrumental in the efforts to enact into law the observance of Veterans Day.

Agreed to October 31, 2003.

FromEmporiaKS (talk) 03:21, 7 February 2017 (UTC)

The first Veterans Day took place in Emporia, Kansas a full year ahead of the Representative Rees introduced the bill to Congress. The source of this information is a first person account by my late friend, Tom Tholen, who help plan the event with Al King and his friends. A printed program of the day's event is available at the Lyon County History Center, Emporia, Kansas, 66801.FromEmporiaKS (talk) 03:21, 7 February 2017 (UTC)

- -  - - - - Joetho (talk) 23:18, 10 November 2019 (UTC)It has been ages since I have edited a wikipedia page (and I will relearn how to do it properly before I propose any edits, I promise) ...but the "History" section of this page appears to be calling my name. Al King lived across the street from us in Emporia KS and the information from inactive/former user "FromEmporiaKs" is true and will be easy to cite. Tom Tholen is my deceased father. I will be working on this, and any help or corrections are welcome. Joetho (talk) 23:18, 10 November 2019 (UTC)

Semi-protected edit request on 13 November 2017
Not all veterans of the military are honored on Veteran's Day. Proclamation 3071—Veteran's Day, 1954 indicates "Veteran's that fought on the seas, in the air, and on Foreign shores". It doesn't say "All that Served" in the military because not all that were in the military were in a war on foreign shores. To honor people that didn't fight brings dishonor to the day.

See for yourself. Now, Therefore, I, Dwight D. Eisenhower, President of the United States of America, do hereby call upon all of our citizens to observe Thursday, November 11, 1954, as Veterans Day. On that day let us solemnly remember the sacrifices of all those who fought so valiantly, on the seas, in the air, and on foreign shores, to preserve our heritage of freedom, and let us reconsecrate ourselves to the task of promoting an enduring peace so that their efforts shall not have been in vain. I also direct the appropriate officials of the Government to arrange for the display of the flag of the United States on all public buildings on Veterans Day. 170.202.22.2 (talk) 20:50, 13 November 2017 (UTC)
 * Red question icon with gradient background.svg Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format. — KuyaBriBri Talk 21:09, 13 November 2017 (UTC)

Semi-protected edit request on 6 October 2018
alslo check http://aveteransday.com Rdritik (talk) 07:14, 6 October 2018 (UTC)
 * Not sure what it is you want done here. Fyunck(click) (talk) 07:38, 6 October 2018 (UTC)

Semi-protected edit request on 7 November 2019
How Donald Trump saved the Veterans' Day Parade

I think it's important to note how Donald Trump funded and saved the parade for decades to come. 38.112.182.5 (talk) 15:45, 7 November 2019 (UTC)
 * Red question icon with gradient background.svg Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format and provide a reliable source if appropriate. — KuyaBriBri Talk 16:33, 7 November 2019 (UTC)

11-11-11
Hey all- should "11-11-11" be displayed somewhere on the page, maybe in parentheses? We have a redirect 11/11/11. Geographyinitiative (talk) 20:02, 11 November 2020 (UTC)
 * The lead states: Major hostilities of World War I were formally ended at the 11th hour of the 11th day of the 11th month of 1918. Is that not sufficient? NedFausa (talk) 20:06, 11 November 2020 (UTC)
 * Thanks for your reply. To me, it is not self evident that English speakers would naturally write 11-11-11 or 11/11/11 based on the passage you just quoted. I would think that 11-11-11 referred to November 11, 1911 or 2011 if I didn't know better- cf. where the user says "11/11/11 takes place every hundred years. In 2011, the 11th November falls on a Friday. There will be a few known global events taking place on 11/11/11". For this reason, it seems like there could be content worthy of a parenthetical mention of some kind in the body of the article. Geographyinitiative (talk) 20:10, 11 November 2020 (UTC) (modified)

Sources and Citations
Hello! I am hoping to improve this article by citing information and adding reliable sources and noticed that the following sentences weren't cited. I tried to see where the information came from and it led me to an opinion blog by a lawyer. This information is quoted directly from the source: "Another military holiday that also occurs in May, Armed Forces Day, honors those currently serving in the U.S. military. Additionally, Women Veterans Day is recognized by a growing number of U.S. states that specifically honors women who have served in the U.S. military." Since this information came from a blog, I think that it should be deleted and replaced with similar information from a reliable source. StudiousBear23 (talk) 13:21, 17 March 2021 (UTC)

Hi all! As I keep adding citations where they are needed I have found a lot of the information is being directly quoted from unreliable sources like blogs and random articles. For instance, the following formation came from a news platform called heavy.com : "Non-essential federal government offices are closed. No mail is delivered. All federal workers are paid for the holiday; those who are required to work on the holiday sometimes receive holiday pay for that day in addition to their wages". The original source says "On Veterans Day, non-essential federal government offices are closed. There is no mail is delivered, and all federal workers are paid for the holiday. Any federal workers who are required to work on the holiday will receive holiday pay for that day in addition to their wages." This information needs to be rewritten as it is almost word-for-word. StudiousBear23 (talk) 13:38, 17 March 2021 (UTC)

The last sentence in the history section is a direct quote from A Stamp A Day website. "While the legal holiday remains on November 11, if that date happens to be on a Saturday or Sunday, then organizations that formally observe the holiday will normally be closed on the adjacent Friday or Monday, respectively". This is quoted almost word-for-word. This is the website link: https://stampaday.wordpress.com/2016/11/11/veterans-day/ StudiousBear23 (talk) 15:36, 17 March 2021 (UTC)

Semi-protected edit request on 11 November 2021 - grammatical mistake in 1st sentence
The first sentence of the article states that Veterans Day is "...for honoring military veterans who served in the United States Armed Forces (that were discharged under conditions other than dishonorable)."

The first word of the parenthetical clause is a relative pronoun referring to veterans. Veterans are people, not objects, and the word veterans is a plural group of individual people; both cases dictate replacing "that" with "who" so that the clause in parentheses reads "military veterans ... who were discharged ..." Revcor632 (talk) 18:23, 11 November 2021 (UTC)
 * ✅ ScottishFinnishRadish (talk) 18:31, 11 November 2021 (UTC)
 * Thank you 2601:380:8201:24C0:BD54:3798:80BB:BDDA (talk) 03:04, 11 November 2023 (UTC)

Kurt Vonnegut’s Breakfast Of Champions
In the famous American Writer’s book of the 1960’s America, Kurt Vonnegut in a dialogur between one of the characters in the book, with a certain truck driver, the two end up having a quick dialogue about American veterans and the famous Veterans Day. The Africanstar Review (talk) 08:59, 11 November 2022 (UTC)

Semi-protected edit request on 10 November 2023
It is stated that Woodrow Wilson issued a message on the First Armistice Day in 1919. In fact, the actual first Armistice Day was when the treaty was signed in 1918, ending World War One.

Therefore, the first paragraph in the history section should be edited to indicate that it was the second Armistice Day, or the first Annual observance of Armistice, to honor the veterans that served, and remember the ones gave it all and didn't return alive. CodexA1 (talk) 00:56, 10 November 2023 (UTC)
 * Red information icon with gradient background.svg Not done: please provide reliable sources that support the change you want to be made. —TechnoSquirrel69 (sigh) 04:42, 10 November 2023 (UTC)

title: Talk:Veterans Day


text:
Guru (rapper)

Keith Edward Elam (July 17, 1961 – April 19, 2010), better known by his stage name Guru (a backronym for Gifted Unlimited Rhymes Universal), was an American rapper, record producer and actor. He was a member of the hip hop duo Gang Starr, along with DJ Premier. He was born in Boston, Massachusetts.

In 2012, About.com placed him #49 on their list of Top 50 MCs of Our Time, and The Source ranked him #30 on their list of Top 50 Lyricists of All Time, saying "Guru dropped some of the most thoughtful rhymes on wax".

Guru died on April 19, 2010, from myeloma at age 48.

Early life
Elam was born in the Roxbury neighborhood of Boston, Massachusetts. His father, Harry Justin Elam served both as a judge and a lawyer and he became the first African American judge appointed to the Boston Municipal Court of Massachusetts and he later also became Chief Justice of the same court and finally as a judge he was appointed as an Associate Justice of the Massachusetts Superior Court. Prior to his judgeship years, between 1971 and 1988, he was a prominent lawyer in the city of Boston from 1952 to 1971 and his mother, Barbara, was the co-director of libraries in the Boston Public Schools system. He attended the Advent School on Beacon Hill in Boston, Noble and Greenough School in Dedham, Massachusetts, and Cohasset High School in Cohasset, Massachusetts for high school. Elam graduated with a degree in business administration from Morehouse College in Atlanta and took graduate classes at the Fashion Institute of Technology in Manhattan.

Musical career
Elam began his music career under the pseudonym MC Keithy E but later changed his stage name to Guru. He founded Gang Starr in 1987. The group initially released three records, produced by The 45 King, on the Wild Pitch Records record label, but these records received little attention. After a change in lineup, the group consisted of rapper Guru and producer DJ Premier. Gang Starr released its first LP No More Mr. Nice Guy on Wild Pitch Records; the group achieved a sizable following and released six critically acclaimed and influential albums from 1989 to 2003. Two albums, Moment of Truth (1998) and compilation Full Clip: A Decade of Gang Starr (1999) were certified gold in the United States by the RIAA. Gang Starr made archetypal East Coast hip hop with Guru's rhyming described as sharp-eyed but anti-ostentatious.

In 1993, Guru released the first in a series of four solo albums while still a member of Gang Starr. Jazzmatazz, Vol. 1 featured collaborations with Donald Byrd, N'Dea Davenport, MC Solaar and Roy Ayers and received positive reviews. His second solo LP, Jazzmatazz, Vol. 2: The New Reality, featured Chaka Khan, Ramsey Lewis, Branford Marsalis and Jamiroquai. The third installment, Jazzmatazz, Vol. 3: Streetsoul, was released in 2000, but it received less positive reviews. In reference to the Jazzmatazz project, Guru told Pete Lewis of Blues & Soul: "Back around '93—when I first came up with the Jazzmatazz concept—I was noticing how a lot of cats were digging in the crates and sampling jazz breaks to make hip hop records. But while I thought that was cool, I wanted to take it to the next level and actually create a new genre by getting the actual dudes we were sampling into the studio to jam over hip hop beats with some of the top vocalists of the time. You know, the whole thing was experimental, but I knew it was an idea that would spawn some historic music."

In 1994, Guru appeared on the Red Hot Organization's compilation album Stolen Moments: Red Hot + Cool. The album, meant to raise awareness and funds in support of the AIDS epidemic in relation to the African American community, was heralded as the album of the year by Time magazine.

Guru's first solo album not a part the Jazzmatazz series, Baldhead Slick & da Click, was released in 2001 to poor reviews. The album reached #22 on the Billboard R&B/Hip Hop album charts. Version 7.0: The Street Scriptures, was released in 2005 on Guru's own record label, 7 Grand Records. The album was produced by labelmate Solar. It reached #54 on the Billboard R&B albums charts and received mixed reviews.

Guru's final releases were the fourth installment in the Jazzmatazz series, released in June 2007; and Guru 8.0: Lost And Found, released May 19, 2009 (also in collaboration with Solar). A final Gang Starr album, One of the Best Yet, was released in 2019.

Death
On February 28, 2010, Guru went into cardiac arrest and, following surgery, fell into a coma. It was claimed that Guru had briefly awakened from his coma but died on April 19, 2010, at the age of 48, from multiple myeloma, a form of blood cancer. Guru was survived by his parents, three siblings, and a son named Keith Casim. His production partner, Solar, claimed that Guru had momentarily awakened from his coma to compose a letter to the public, although DJ Premier and members of Guru's family stated that he never regained consciousness. Guru's family claimed that Solar had prevented them from having contact with Guru during his illness just before his death; the validity of the deathbed letter was consequently challenged by Guru's family. In an interview on Conspiracy Worldwide Radio, Solar claimed that he was protective of Guru, and everything he had said was true. This interview was met by extreme emotion from the hip hop community and did little to clear the controversy surrounding his actions.

DJ Premier produced a tribute mix to Guru and has released a public letter along with Guru's sister Patricia Elam. Harry J. Elam, an older brother, wrote a personal memoir in remembrance published in The Boston Globe on April 23, 2010. The Elam family had a Guru tribute website set up where visitors were able to view tributes and sign a memorial page. Guru's nephew Justin Nicholas-Elam Ruff made a 16-minute documentary in which he narrated the story of his late uncle.

At the 2011 Grammy Awards, Guru's name was not mentioned in the annual retrospective of musicians who had died since the 2010 awards. On April 21, 2011, Revive Da Live Big Band held a tribute show for Guru at Le Poisson Rouge in New York City. The show paid homage to Guru's Jazzmatazz series and featured a full jazz band tribute, with all proceeds going towards the Elam family. During the concert, Babygrande Records donated $5000 to Guru's son, K.C. Elam.

Legacy
The French city of Montpellier named a small street "Allée Guru" after the rapper, citing his influence on both hip hop and jazz.

Discography

 * Studio albums
 * Guru's Jazzmatazz, Vol. 1 (1993)
 * Guru's Jazzmatazz, Vol. 2: The New Reality (1995)
 * Guru's Jazzmatazz, Vol. 3: Streetsoul (2000)
 * Baldhead Slick & da Click (2001)
 * Version 7.0: The Street Scriptures (2005)
 * Guru's Jazzmatazz, Vol. 4: The Hip Hop Jazz Messenger: Back to the Future (2007)
 * Guru 8.0: Lost and Found (2009)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Guru (rapper)


text:
Circle of confusion

In optics, a circle of confusion (CoC) is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source. It is also known as disk of confusion, circle of indistinctness, blur circle, or blur spot.

In photography, the circle of confusion is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. Usages in context include maximum permissible circle of confusion, circle of confusion diameter limit, and the circle of confusion criterion.

Real lenses do not focus all rays perfectly, so that even at best focus, a point is imaged as a spot rather than a point. The smallest such spot that a lens can produce is often referred to as the circle of least confusion.

Two uses
Two important uses of this term and concept need to be distinguished:

In idealized ray optics, where rays are assumed to converge to a point when perfectly focused, the shape of a defocus blur spot from a lens with a circular aperture is a hard-edged circle of light. A more general blur spot has soft edges due to diffraction and aberrations, and may be non-circular due to the aperture shape. Therefore, the diameter concept needs to be carefully defined in order to be meaningful. Suitable definitions often use the concept of encircled energy, the fraction of the total optical energy of the spot that is within the specified diameter. Values of the fraction (e.g., 80%, 90%) vary with application.

Circle of confusion diameter limit in photography
In photography, the circle of confusion diameter limit (CoC limit or CoC criterion) is often defined as the largest blur spot that will still be perceived by the human eye as a point, when viewed on a final image from a standard viewing distance. The CoC limit can be specified on a final image (e.g. a print) or on the original image (on film or image sensor).

With this definition, the CoC limit in the original image (the image on the film or electronic sensor) can be set based on several factors:

The common values for CoC limit may not be applicable if reproduction or viewing conditions differ significantly from those assumed in determining those values. If the original image will be given greater enlargement, or viewed at a closer distance, then a smaller CoC will be required. All three factors above are accommodated with this formula:

CoC (in mm) = (viewing distance (in cm) / 25 cm ) / (desired final-image resolution in lp/mm for a 25 cm viewing distance) / enlargement

For example, to support a final-image resolution equivalent to 5 lp/mm for a 25 cm viewing distance when the anticipated viewing distance is 50 cm and the anticipated enlargement is 8:

CoC = (50 / 25) / 5 / 8 = 0.05 mm

Since the final-image size is not usually known at the time of taking a photograph, it is common to assume a standard size such as 25 cm width, along with a conventional final-image CoC of 0.2 mm, which is 1/1250 of the image width. Conventions in terms of the diagonal measure are also commonly used. The DoF computed using these conventions will need to be adjusted if the original image is cropped before enlarging to the final image size, or if the size and viewing assumptions are altered.

For full-frame 35 mm format (24 mm × 36 mm, 43 mm diagonal), a widely used CoC limit is $L$/1500, or 0.029 mm for full-frame 35 mm format, which corresponds to resolving 5 lines per millimeter on a print of 30 cm diagonal. Values of 0.030 mm and 0.033 mm are also common for full-frame 35 mm format.

Criteria relating CoC to the lens focal length have also been used. Kodak recommended 2 minutes of arc (the Snellen criterion of 30 cycles/degree for normal vision) for critical viewing, yielding a CoC of about $F$/1720, where $L$ is the lens focal length. For a 50 mm lens on full-frame 35 mm format, the corresponding CoC is 0.0291 mm. This criterion evidently assumed that a final image would be viewed at perspective-correct distance (i.e., the angle of view would be the same as that of the original image):

Viewing distance = focal length of taking lens × enlargement

However, images seldom are viewed at the so-called 'correct' distance; the viewer usually does not know the focal length of the taking lens, and the "correct" distance may be uncomfortably short or long. Consequently, criteria based on lens focal length have generally given way to criteria (such as $C$/1500) related to the camera format.

If an image is viewed on a low-resolution display medium such as a computer monitor, the detectability of blur will be limited by the display medium rather than by human vision. For example, the optical blur will be more difficult to detect in an 8 in × 10 in image displayed on a computer monitor than in an 8×10 print of the same original image viewed at the same distance. If the image is to be viewed only on a low-resolution device, a larger CoC may be appropriate; however, if the image may also be viewed in a high-resolution medium such as a print, the criteria discussed above will govern.

Depth of field formulas derived from geometrical optics imply that any arbitrary DoF can be achieved by using a sufficiently small CoC. Because of diffraction, however, this is not quite true. Using a smaller CoC requires increasing the lens f-number to achieve the same DoF, and if the lens is stopped down sufficiently far, the reduction in defocus blur is offset by the increased blur from diffraction. See the Depth of field article for a more detailed discussion.

Adjusting the circle of confusion diameter for a lens's DoF scale
The f-number determined from a lens DoF scale can be adjusted to reflect a CoC different from the one on which the DoF scale is based. It is shown in the Depth of field article that

$$\mathrm {DoF} = \frac {2 N c \left ( m + 1 \right )} {m^2 - \left ( \frac {N c} {f} \right )^2} \,, $$

where $d$ is the lens f-number, $f$ is the CoC, $f$ is the magnification, and $d$ is the lens focal length. Because the f-number and CoC occur only as the product $d$, an increase in one is equivalent to a corresponding decrease in the other. For example, if it is known that a lens DoF scale is based on a CoC of 0.035 mm, and the actual conditions require a CoC of 0.025 mm, the CoC must be decreased by a factor of 0.035 / 0.025 = 1.4; this can be accomplished by increasing the f-number determined from the DoF scale by the same factor, or about 1 stop, so the lens can simply be closed down 1 stop from the value indicated on the scale.

The same approach can usually be used with a DoF calculator on a view camera.

Determining a circle of confusion diameter from the object field

To calculate the diameter of the circle of confusion in the image plane for an out-of-focus subject, one method is to first calculate the diameter of the blur circle in a virtual image in the object plane, which is simply done using similar triangles, and then multiply by the magnification of the system, which is calculated with the help of the lens equation.

The blur circle, of diameter $56 mm$, in the focused object plane at distance $S_{2}$, is an unfocused virtual image of the object at distance $S_{1}$ as shown in the diagram. It depends only on these distances and the aperture diameter $69 mm$, via similar triangles, independent of the lens focal length:

$$ C = A {|S_2 - S_1| \over S_2} \,.$$

The circle of confusion in the image plane is obtained by multiplying by magnification $15 mm$:

$$ c = C m \,,$$

where the magnification $22.5 mm$ is given by the ratio of focus distances:

$$ m = {f_1 \over S_1} \,.$$

Using the lens equation we can solve for the auxiliary variable $S_{1}$:

$$ {1 \over f} = {1 \over f_1} + {1 \over S_1} \,,$$

which yields

$$ f_1 = {f S_1 \over S_1 - f} \,,$$

and express the magnification in terms of focused distance and focal length:

$$ m = {f \over S_1 - f} \,,$$

which gives the final result:

$$ c = A {|S_2 - S_1| \over S_2} {f \over S_1 - f} \,.$$

This can optionally be expressed in terms of the f-number $S_{2}$ as:

$$ c = {|S_2 - S_1| \over S_2} {f^2 \over N(S_1 - f)} \,.$$

This formula is exact for a simple paraxial thin lens or a symmetrical lens, in which the entrance pupil and exit pupil are both of diameter $16 mm$. More complex lens designs with a non-unity pupil magnification will need a more complex analysis, as addressed in depth of field.

More generally, this approach leads to an exact paraxial result for all optical systems if $24 mm$ is the entrance pupil diameter, the subject distances are measured from the entrance pupil, and the magnification is known:

$$ c = A m {|S_2 - S_1| \over S_2} \,.$$

If either the focus distance or the out-of-focus subject distance is infinite, the equations can be evaluated in the limit. For infinite focus distance:

$$ c = {f A \over S_2} = {f^2 \over N S_2} \,.$$

And for the blur circle of an object at infinity when the focus distance is finite:

$$ c = {f A \over S_1 - f} = {f^2 \over N(S_1 - f)} \,.$$

If the $N$ value is fixed as a circle of confusion diameter limit, either of these can be solved for subject distance to get the hyperfocal distance, with approximately equivalent results.

Henry Coddington 1829
Before it was applied to photography, the concept of circle of confusion was applied to optical instruments such as telescopes. quantifies both a circle of least confusion and a least circle of confusion for a spherical reflecting surface.

"This we may consider as the nearest approach to a simple focus, and term the circle of least confusion."

Society for the Diffusion of Useful Knowledge 1832
The applied it to third-order aberrations:

"This spherical aberration produces an indistinctness of vision, by spreading out every mathematical point of the object into a small spot in its picture; which spots, by mixing with each other, confuse the whole. The diameter of this circle of confusion, at the focus of the central rays F, over which every point is spread, will be L K (fig. 17.); and when the aperture of the reflector is moderate it equals the cube of the aperture, divided by the square of the radius (...): this circle is called the aberration of latitude."

T.H. 1866
Circle-of-confusion calculations: An early precursor to depth of field calculations is the calculation of a circle-of-confusion diameter from a subject distance, for a lens focused at infinity; this article was pointed out by. The formula he comes up with for what he terms "the indistinctness" is equivalent, in modern terms, to

$$c = {f A \over S}$$

for focal length $c$, aperture diameter $m$, and subject distance $f$. But he does not invert this to find the $Nc$ corresponding to a given $c$ criterion (i.e. he does not solve for the hyperfocal distance), nor does he consider focusing at any other distance than infinity.

He finally observes "long-focus lenses have usually a larger aperture than short ones, and on this account have less depth of focus" [his italic emphasis].

Dallmeyer and Abney
, in an expanded re-publication of his father John Henry Dallmeyer's 1874 pamphlet On the Choice and Use of Photographic Lenses (in material that is not in the 1874 edition and appears to have been added from a paper by J.H.D. "On the Use of Diaphragms or Stops" of unknown date), says:

"Thus every point in an object out of focus is represented in the picture by a disc, or circle of confusion, the size of which is proportionate to the aperture in relation to the focus of the lens employed. If a point in the object is 1/100 of an inch out of focus, it will be represented by a circle of confusion measuring but 1/100 part of the aperture of the lens."

This latter statement is clearly incorrect, or misstated, being off by a factor of focal distance (focal length). He goes on:

"and when the circles of confusion are sufficiently small the eye fails to see them as such; they are then seen as points only, and the picture appears sharp. At the ordinary distance of vision, of from twelve to fifteen inches, circles of confusion are seen as points, if the angle subtended by them does not exceed one minute of arc, or roughly, if they do not exceed the 1/100 of an inch in diameter."

Numerically, 1/100 inch at 12–15 inches is closer to two minutes of arc. This choice of CoC limit remains (for a large print) the most widely used even today. takes a similar approach based on a visual acuity of one minute of arc, and chooses a circle of confusion of 0.025 cm for viewing at 40–50 cm, essentially making the same factor-of-two error in metric units. It is unclear whether Abney or Dallmeyer was earlier to set the CoC standard thereby.

Wall 1889
The common 1/100 inch CoC limit has been applied to blur other than defocus blur. For example, says:

"To find how quickly a shutter must act to take an object in motion that there may be a circle of confusion less than 1/100 in. in diameter, divide the distance of the object by 100 times the focus of the lens, and divide the rapidity of motion of object in inches per second by the results, when you have the longest duration of exposure in fraction of a second."

title: Circle of confusion


text:
Kingdom of Ireland

The Kingdom of Ireland (Ríoghacht Éireann; Ríocht na hÉireann, ) was a dependent territory of England and then of Great Britain that existed from 1542 to the end of 1800. It was ruled by the monarchs of England and then of Great Britain, and was administered from Dublin Castle by a viceroy appointed by the English king: the Lord Deputy of Ireland. Aside from brief periods, the state was dominated by the Protestant English (or Anglo-Irish) minority. The Protestant Church of Ireland was the state church. The Parliament of Ireland was composed of Anglo-Irish nobles. From 1661, the administration controlled an Irish army. Although styled a kingdom, for most of its history it was, de facto, an English dependency. This status was enshrined in Poynings' Law and in the Declaratory Act of 1719.

The territory of the kingdom comprised that of the former Lordship of Ireland, founded in 1177 by King Henry II of England and the English Pope Adrian IV, after the Anglo-Norman invasion of Ireland. By the 16th century, the Pale, the area of effective English rule, had shrunk greatly; most of Ireland was held by Gaelic nobles as principalities and chiefdoms. By the terms of the Crown of Ireland Act 1542, Henry VIII of England became "King of Ireland". There followed an expansion of English control during the Tudor conquest. This sparked the Desmond Rebellions and the Nine Years' War. The conquest of the island was completed early in the 17th century. It involved the confiscation of land from the native Irish Catholics and its colonisation by Protestant settlers from Britain. Catholic countries at the time did not recognise Protestant monarchs as kings of Ireland.

For most of the kingdom's history, the Irish Catholic majority suffered official discrimination: under the penal laws, Catholicism was suppressed and Catholics were barred from government, parliament, the military, and most public offices. This was one of the main drivers behind the Irish Confederate Wars (1641–53), during which the Irish Catholic Confederates controlled most of Ireland. After the Cromwellian conquest, Ireland suffered harsh conditions under The Protectorate (1653–59). The brief reign of Catholic king James II (1685–89) led to the Williamite War (1689–91). The Williamite victory strengthened the Protestant Ascendancy, and the kingdom had only Protestant monarchs thereafter.

In the 1780s, the parliament gained some independence, and some anti-Catholic laws were lifted. This sparked sectarian conflict in County Armagh. Following the failed republican Irish Rebellion of 1798, the parliament of Ireland and parliament of Great Britain passed the Acts of Union 1800. This created, on 1 January 1801, the United Kingdom of Great Britain and Ireland and the Parliament of the United Kingdom.

Background
The papal bull Laudabiliter of Pope Adrian IV was issued in 1155. It granted the Angevin King Henry II of England the title Dominus Hibernae (Latin for "Lord of Ireland"). Laudabiliter authorised the king to invade Ireland, to bring the country into the European sphere. In return, Henry was required to remit a penny per hearth of the tax roll to the Pope. This was reconfirmed by Adrian's successor Pope Alexander III in 1172.

When Pope Clement VII excommunicated the king of England, Henry VIII, in 1533, the constitutional position of the lordship in Ireland became uncertain. Henry had broken away from the Holy See and declared himself the head of the Church in England. He had petitioned Rome to procure an annulment of his marriage to Catherine of Aragon. Clement VII refused Henry's request and Henry subsequently refused to recognise the Roman Catholic Church's vestigial sovereignty over Ireland, and was excommunicated again in late 1538 by Pope Paul III. The Treason Act (Ireland) 1537 was passed to counteract this.

Tudor Ireland
Following the failed revolt of Silken Thomas in 1534–35, Grey, the lord deputy, had some military successes against several clans in the late 1530s, and took their submissions. By 1540 most of Ireland seemed at peace and under the control of the king's Dublin administration; a situation that was not to last for long.

In 1542, the Kingdom of Ireland was established by the Parliament of Ireland through the Crown of Ireland Act. This act declared King Henry VIII of England as the King of Ireland, thus creating a separate political entity known as the Kingdom of Ireland. The act marked a significant shift in Ireland's political landscape, as it sought to consolidate English control over the island and bring it under closer royal governance. The Kingdom of Ireland existed alongside the Lordship of Ireland, which was held by the English monarchs prior to the establishment of the kingdom. The new kingdom was not recognised by the Catholic monarchies in Europe. After the death of Edward VI, Henry's son, the papal bull of 1555 recognised the Roman Catholic Mary I as Queen of Ireland. The link of "personal union" of the Crown of Ireland to the Crown of England became enshrined in Catholic canon law. In this fashion, the Kingdom of Ireland was ruled by the reigning monarch of England. This placed the new Kingdom of Ireland in personal union with the Kingdom of England.

In line with its expanded role and self-image, the administration established the King's Inns for barristers in 1541, and the Ulster King of Arms to regulate heraldry in 1552. Proposals to establish a university in Dublin were delayed until 1592.

In 1593 war broke out, as Hugh O'Neill, Earl of Tyrone, led a confederation of Irish lords and Spain against the crown, in what later became known as the Nine Years' War. A series of stunning Irish victories brought English power in Ireland to the point of collapse by the beginning of 1600, but a renewed campaign under Charles Blount, Lord Mountjoy forced Tyrone to submit in 1603, completing the Tudor conquest of Ireland.

Stuart Ireland
In 1603 James VI King of Scots became James I of England and Ireland, uniting the Kingdoms of England, Scotland and Ireland in a personal union. James established the Plantation of Ulster in 1606, the largest of all English and Scottish plantations in Ireland. It had a lasting legacy; into the 20th century, most of Ulster had a Protestant and Pro-Union majority in its population.

The political order of the kingdom was interrupted by the Wars of the Three Kingdoms starting in 1639. During the subsequent interregnum period, England, Scotland and Ireland were ruled as a republic until 1660. This period saw the rise of the loyalist Irish Catholic Confederation within the kingdom and, from 1653, the creation of the republican Commonwealth of England, Scotland and Ireland. The kingdom's order was restored 1660 with the restoration of Charles II. Without any public dissent, Charles's reign was backdated to his father's execution in 1649.

Grattan's Patriots
Poynings' Law was repealed in 1782 in what came to be known as the Constitution of 1782, granting Ireland legislative independence. Parliament in this period came to be known as Grattan's Parliament, after the principal Irish leader of the period, Henry Grattan. Although Ireland had legislative independence, executive administration remained under the control of the executive of the Kingdom of Great Britain. In 1788–1789 a Regency crisis arose when King George III became ill. Grattan wanted to appoint the Prince of Wales, later George IV, as Regent of Ireland. The king recovered before this could be enacted.

United Irishmen

The Irish Rebellion of 1798, and the rebels' alliance with Great Britain's longtime enemy the French, led to a push to bring Ireland formally into the British Union. By the Acts of Union 1800, voted for by both Irish and British Parliaments, the Kingdom of Ireland merged on 1 January 1801 with the Kingdom of Great Britain to form the United Kingdom of Great Britain and Ireland. The Irish Parliament ceased to exist, though the executive, presided over by the Lord Lieutenant, remained in place until 1922.

Viceroy
The Kingdom of Ireland was governed by a Lord Deputy or viceroy. The post was held by senior nobles such as Thomas Radcliffe. From 1688 the title was usually Lord Lieutenant. In the absence of a Lord Deputy, lords justices ruled. While some Irishmen held the post, most of the lords deputy were English noblemen. While the viceroy controlled the Irish administration as the monarch's representative, in the eighteenth century the political post of Chief Secretary for Ireland became increasingly powerful.

Parliament
The kingdom's legislature was bicameral with a House of Lords and a House of Commons. By the terms of Poynings' Law (1494) and other acts, the parliament's powers were greatly circumscribed. The legislature was content to "rubber stamp" acts or "suggestions" from the English parliament.

Roman Catholics and dissenters, mostly Presbyterians, Baptists, and Methodists, were excluded from membership of the Irish parliament from 1693. Furthermore, their rights were restricted by a series of laws called the Penal Laws. They were denied voting rights from 1728 until 1793. The Grattan Parliament succeeded in achieving the repeal of Poynings' Law in 1782. This allowed progressive legislation and gradual liberalisation was effected. Catholics and Dissenters were given the right to vote in 1793, but Catholics were still excluded from the Irish Parliament and senior public offices in the kingdom. As in Great Britain and the rest of Europe, voting and membership of parliament was restricted to property owners. In the 1720s, the parliament was housed in a new building at College Green, Dublin.

Church of Ireland

When Henry VIII was excommunicated by the Catholic Church in 1538, all but two of the bishops in the island of Ireland followed the doctrine of the Church of England, although almost no clergy or laity did so. Having paid their Annates to the Papacy, the bishops had no reason to step down, and in the 1530s nobody knew how long the reformation would last. Unlike Henry VIII, this hierarchy was not excommunicated by the Papacy. They retained control of what became the State Church of the new Kingdom in 1542. As the established church, it retained possession of most Church property (including a great repository of religious architecture and other items, though some were later destroyed). In 1553, Irish Catholics were heartened by the coronation of Queen Mary I. In 1555, she persuaded the Pope to recognise the Kingdom in the papal bull "Ilius".

In 1558, a Protestant – Elizabeth I – ascended the throne. With the exception of James II of England, all the following monarchs adhered to Anglicanism. Contrary to the official plan, the substantial majority of the population remained strongly Roman Catholic, despite the political and economic advantages of membership of the state church. Despite its numerical minority, however, the Church of Ireland remained the official state church until it was disestablished on 1 January 1871 by the Liberal government under William Ewart Gladstone.

Ethnic conflict
The legacy of the Kingdom of Ireland remains a bone of contention in Irish-British relations to this day because of the constant ethnic conflict between the native Irish inhabitants and primarily the new Anglo-Irish settlers across the island. Their background espoused English culture (law, language, dress, religion, economic relations and definitions of land ownership) in Ireland as it later did across much of what was to become the British Empire. However Gaelic culture and Irish language, was maintained to a significant extent by the majority of the original native population. Sometimes this was presented as "barbaric", "savage" which later was perceived by the native population as a mark of undesirability in respect of maintaining and learning the language. While the Lordship of Ireland had existed since the 12th century and nominally owed allegiance to the English monarchy, many kingdoms of Gaelic Ireland continued to exist; this came to an end with the Kingdom of Ireland, where the whole island was brought under the centralised control of an Anglo-centric system based in Dublin. This phase of Irish history marked the beginning of an officially organised policy of settler colonialism, orchestrated from London and the incorporation of Ireland into the British Empire (indeed Ireland is sometimes called "England's first colony"). The theme is prominently addressed in Irish postcolonial literature.

The religion of the native majority and its clergy – the Catholic Church – was actively persecuted by the state. A set of Penal Laws favoured those who adhered to the established church – the Church of Ireland. They oppressed those native Irish who refused to abjure their religion. A similar experience happened to English, Scottish and Welsh Catholics during the same period. There is some perception that during Tudor times, elements within the government at times engaged in and advanced a genocidal policy against the Irish Gaels, while during the Plantations of Ireland (particularly successful in Ulster) the local population were displaced in a project of ethnic cleansing where regions of Ireland became de-Gaelicised. This in turn led to bloody retaliations, which drag on to modern times. Some of the native inhabitants, including their leadership, were permitted to flee into exile from the country following ending up on the losing side in conflicts (i.e. the Flight of the Earls and the Flight of the Wild Geese) or in the case of the Cromwellian regime were forced into indentured servitude (although the same happened to English persons involved in the Cromwellian regime) in the Caribbean, following mass land confiscation for the benefit of New English settlers.

On the other hand, the fact that the kingdom had been a unitary state gave Irish nationalists in 1912–22 a reason to expect that in the process of increasing self-government the island of Ireland would be treated as a single political unit.

Coat of arms

The arms of the Kingdom of Ireland were blazoned: Azure, a harp Or stringed Argent. These earliest arms of Ireland are described in an entry that reads: Le Roi d'Irlande, D'azur à la harpe d'or, in a 13th-century French roll of arms, the Armorial Wijnbergen, also known as the Wijnbergen Roll, said to be preserved in The Hague, in the Netherlands but currently untraced; a copy is held in the Royal Library of Belgium (Collection Goethals, ms. 2569). This may have been an aspirational depiction for a putative High-King, for it was not related to the Lordship of Ireland at that time by the English king, who only assumed the title "King of Ireland" later in the reign of Henry VIII

A crown was not part of the arms but use of a crowned harp was apparently common as a badge or as a device. A crowned harp also appeared as a crest although the delineated crest was: a wreath Or and Azure, a tower (sometime triple-towered) Or, from the port, a hart springing Argent.

"King James not only used the harp crowned as the device of Ireland, but quartered the harp in this royal achievement for the arms of that kingdom, in the third quarter of the royal achievement upon his Great Seal, as it has continued ever since. The blazon was azure, a harp or string argent, as appears by the great embroidered banner, and at the funeral of Queen Anne, King James' queen, AD 1618, and likewise by the great banner and banner of Ireland at the funeral of King James. The difference between the arms and device of Ireland appears to be on the crown only, which is added to the harp when used as a device.

At the funeral of King James was likewise carried the standard of the crest of Ireland, a buck proper (argent in the draught) issuing from a tower triple towered or, which is the only instance of this crest that I have met, and therefore was probably devised and assigned for the crest of Ireland upon occasion of this funeral, but with what propriety I do not understand."

"The insignia of Ireland have variously been given by early writers. In the reign of Edward IV, a commission appointed to enquire what were the arms of Ireland found them to be three crowns in pale. It has been supposed that these crowns were abandoned at the Reformation, from an idea that they might denote the feudal sovereignty of the pope, whose vassal the king of England was, as lord of Ireland. However, in a manuscript in the Heralds' College of the time of Henry VII, the arms of Ireland are blazoned azure, a harp or, stringed argent; and when they were for the first time placed on the royal shield on the accession of James I. they were thus delineated: the crest is on a wreath or and azure, a tower (sometime triple-towered) or, from the port, a hart springing argent. Another crest is a harp or. The national flag of Ireland exhibits the harp in a field vert. The royal badge of Ireland, as settled by sign-manual in 1801 is a harp, or, stringed argent, and a trefoil vert, both ensigned with the imperial crown."

title: Kingdom of Ireland


text:
Talk:Richard Threlkeld Cox

Untitled
Is he consistantly called "Richard Threlkeld Cox"? We tend not to include middle names in article titles unless it's the name the person is normally known by. -- Zoe

 * No. He's called "Richard Cox" or sometimes "Richard T. Cox", but I think the person who moved the article to "Richard Threlkeld Cox" said "Richard Cox" is "a disambiguation waiting to happen".  "Richard" and "Cox" are commonplace names and it's not hard to imagine that "Richard Cox"s will become subjects of Wikipedia articles.  -- Mike Hardy

 * "Richard Cox" is also a juvenile vandalism waiting to happen. FWIW, there was a "Richard Threlkeld" who was a foreign correspondent for CBS. Ortolan88

 * So how about Richard L. Cox? -- Zoe

title: Talk:Richard Threlkeld Cox


text:
Talk:Circle of confusion

Love the mm and " mixed in the same paragraphs with no relation or equivalence ... not
Yeah, see "... Viewing conditions. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate. A comfortable viewing distance is also one at which the angle of view is approximately 60° (Ray 2000, 52); at a distance of 25 cm, this corresponds to about 30 cm, approximately the diagonal of an 8″×10″ image (A4 paper is ~8"×11″) ..."

So, who wants to link mm and inches equivalents for every dimension reference?

68.100.25.247 (talk) 04:41, 12 August 2020 (UTC)
 * You could use the convert template. For example  renders as: 25 cm Vexations (talk) 11:04, 12 August 2020 (UTC)

Human vision resolution
"Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision (Ray 2000, 52), is approximately 25 cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image."

If we have 5 lp/mm this is actually 10 dots per mm (dpmm), as for each line we need 2 dots, one black and one white. So is it not the appropriate CoC of 0,1 mm rather than 0,2 mm? This is than related with the critical print resolution of 300 dpi or 12 dpmm and CoC of 0,085 mm.

Thanks for an answer

84.52.165.129 (talk) 21:47, 24 March 2012 (UTC) Rajko Bizjak 84.52.165.129 (talk) 21:47, 24 March 2012 (UTC)

 * The key is understanding what resolution means: it means that something is being resolved from something else, for instance two objects side by side look like two objects instead of one bigger one. Let's say the object is a white line of 0.1mm width against a black background.  If two white lines were side by side without gaps they would look like a single thicker line therefore they would not be resolved. So when we speak about a resolution of 5 lp/mm we are really saying that there is a line of width 0.1mm next to a gap of the same size, which we can also consider a line, this time black.   That's the line pair every 0.2mm. But there is only one object per cycle (a white 0.1mm line ).  If the retina is able to 'see' the dark gap between two white lines we can say that it is able to resolve them. We could also say that in those conditions it is able to resolve objects down to 0.1mm repeating every 0.2mm.  The period, hence the CoC, is 0.2mm.
 * This was clear in the late 1800's to Abney and Dallmeyer referenced in the historical section. The average human is said to be able to resolve objects of 1 arc minute size on the retina, repeating every 2 arc minutes.  In lines, that's equivalent to about 30 lp/degree.  Therefore a person with 20/20 vision has a CoC of about 1/30th of a degree on the retina, and Abney and Dallmeyer were correct after all. Jack Hogan (talk) 09:17, 28 March 2024 (UTC)

Not May not do this right: This slide deck talks about the Barten model, j-curve, JNDs and HVS. https://humanhealth.iaea.org/HHW/MedicalPhysics/TheMedicalPhysicist/Studentscorner/HandbookforTeachersandStudents/Chapter_18.pdf

May help explain the terms and why they are.Purduephotog (talk) 20:17, 1 April 2020 (UTC)

Addition to Section "Circle of confusion diameter limit in photography"
Note that this definition of CoC is base for a final image obtained from a 35mm full frame format and that all other formats are enlarged to obtain a final image of the same size. The differences in enlargement causes the difference in the required CoC of the image on the film or sensor to maintain the same CoC of e.g. 0.2mm on the final image. When making identical enlargements from different formats, so an object from the original image, captured at the same focal distance, will have the same size on the final images, the CoC is identical for all formats. Only the outer size of the final image will differ equaly to the difference in size between the formats. Furthermore, in digital photography, a comparison often starts from a 1:1 representation of the sensor pixels on a screen. In this case it will be a differences in the resolution (pixels per inch) of the sensor that will lead to different enlargements. These different approaches to obtain and compare a final image have lead to many misunderstandings and errors when discussing focus and dept of focus differences between sensors of different format and/or resolution.Johnny Swinnen (talk) 23:48, 3 March 2013 (UTC)

Switch to physics conventions?
Whoever created the formulas and diagram used nonstandard notation. The standard notation is "o" for object distance and "i" for image distance. Using nonstandard notation makes the article much less accessible. Does anybody know how the diagram could be changed? That is the most difficult thing to change, the formulas would be easy.

Joel Frederico (talk) 23:32, 26 February 2015 (UTC)

title: Talk:Circle of confusion


text:
Light meter

A light meter (or illuminometer) is a device used to measure the amount of light. In photography, an exposure meter is a light meter coupled to either a digital or analog calculator which displays the correct shutter speed and f-number for optimum exposure, given a certain lighting situation and film speed. Similarly, exposure meters are also used in the fields of cinematography and scenic design, in order to determine the optimum light level for a scene.

Light meters also are used in the general field of architectural lighting design to verify proper installation and performance of a building lighting system, and in assessing the light levels for growing plants.

If a light meter is giving its indications in luxes, it is called a "luxmeter".

Evolution

Actinometers
The earliest exposure meters were called actinometers (not to be confused with the scientific instrument with the same name), first developed in the late 1800s after commercial photographic plates became available with consistent sensitivity. These photographic actinometers used light-sensitive paper; the photographer would measure the time required for the paper to darken to a control value, providing an input to a mechanical calculation of shutter speed and aperture for a given plate number. They were popular between approximately 1890 and 1920.

Extinction types
The next exposure meters, developed at about the same time but not displacing actinometers in popularity until the 1920s and 1930s, are known as extinction meters, evaluating the correct exposure settings by variable attenuation. One type of extinction meter contained a numbered or lettered row of neutral density filters of increasing density. The photographer would position the meter in front of their subject and note the filter with the greatest density that still allowed incident light to pass through. In another example, sold as Heyde's Aktino-Photometer starting from the early 1900s, the photographer views the scene through an eyepiece and turns the meter to vary the effective density until the scene can no longer be seen. The letter or number corresponding to the filter strength causing the "extinction" of the scene was used as an index into a chart of appropriate aperture and shutter speed combinations for a given film speed.

Extinction meters tended to provide inconsistent results because they depended on subjective interpretation and the light sensitivity of the human eye, which can vary from person to person.

Photoelectric types
Later meters removed the human element and relied on technologies incorporating selenium, CdS, and silicon photodetectors.

Selenium and silicon light meters use sensors that are photovoltaic: they generate a voltage proportional to light exposure. Selenium sensors generate enough voltage for direct connection to a meter; they need no battery to operate and this made them very convenient in completely mechanical cameras. Selenium sensors however cannot measure low light accurately (ordinary lightbulbs can take them close to their limits) and are altogether unable to measure very low light, such as candlelight, moonlight, starlight etc. Silicon sensors need an amplification circuit and require a power source such as batteries to operate. CdS light meters use a photoresistor sensor whose electrical resistance changes proportionately to light exposure. These also require a battery to operate. Most modern light meters use silicon or CdS sensors. They indicate the exposure either with a needle galvanometer or on an LCD screen.

Many modern consumer still and video cameras include a built-in meter that measures a scene-wide light level and are able to make an approximate measure of appropriate exposure based on that. Photographers working with controlled lighting and cinematographers use handheld light meters to precisely measure the light falling on various parts of their subjects and use suitable lighting to produce the desired exposure levels.

Reflected and incident measurements
Exposure meters generally are sorted into reflected-light or incident-light types, depending on the method used to measure the scene.

Reflected-light meters measure the light reflected by the scene to be photographed. All in-camera meters are reflected-light meters. Reflected-light meters are calibrated to show the appropriate exposure for "average" scenes. An unusual scene with a preponderance of light colors or specular highlights would have a higher reflectance; a reflected-light meter taking a reading would incorrectly compensate for the difference in reflectance and lead to underexposure. Badly underexposed sunset photos are common exactly because of this effect: the brightness of the setting sun fools the camera's light meter and, unless the in-camera logic or the photographer take care to compensate, the picture will be grossly underexposed and dull.

This pitfall (but not in the setting-sun case) is avoided by incident-light meters which measure the amount of light falling on the subject using a diffuser with a flat or (more commonly) hemispherical field of view placed on top of the light sensor. Because the incident-light reading is independent of the subject's reflectance, it is less likely to lead to incorrect exposures for subjects with unusual average reflectance. Taking an incident-light reading requires placing the meter at the subject's position and pointing it in the general direction of the camera, something not always achievable in practice, e.g., in landscape photography where the subject distance approaches infinity.

Another way to avoid under- or over-exposure for subjects with unusual reflectance is to use a spot meter: a specialized reflected-light meter that measures light in a very tight cone, typically with a one degree circular angle of view. An experienced photographer can take multiple readings over the shadows, midrange, and highlights of the scene to determine optimal exposure, using systems like the Zone System.

Many modern cameras include sophisticated multi-segment metering systems that measure the luminance of different parts of the scene to determine the optimal exposure. When using a film whose spectral sensitivity is not a good match to that of the light meter, for example orthochromatic black-and-white or infrared film, the meter may require special filters and re-calibration to match the sensitivity of the film.

There are other types of specialized photographic light meters. Flash meters are used in flash photography to verify correct exposure. Color meters are used where high fidelity in color reproduction is required. Densitometers are used in photographic reproduction.

Exposure meter calibration
In most cases, an incident-light meter will cause a medium tone to be recorded as a medium tone, and a reflected-light meter will cause whatever is metered to be recorded as a medium tone. What constitutes a "medium tone" depends on meter calibration and several other factors, including film processing or digital image conversion.

Meter calibration establishes the relationship between subject lighting and recommended camera settings. The calibration of photographic light meters is covered by ISO 2720:1974.

Exposure equations
For reflected-light meters, camera settings are related to ISO speed and subject luminance by the reflected-light exposure equation:

$$ \frac {N^2} {t} = \frac {L S} {K} $$

where

 * $$N$$ is the relative aperture (f-number)
 * $$t$$ is the exposure time ("shutter speed") in seconds
 * $$L$$ is the average scene luminance
 * $$S$$ is the ISO arithmetic speed
 * $$K$$ is the reflected-light meter calibration constant

For incident-light meters, camera settings are related to ISO speed and subject illuminance by the incident-light exposure equation:

\frac {N^2} {t} = \frac {E S} {C} $$

where

 * $$E$$ is the illuminance
 * $$C$$ is the incident-light meter calibration constant

Calibration constants
Determination of calibration constants has been largely subjective; ISO 2720:1974 states that

The constants $$K$$ and $$C$$ shall be chosen by statistical analysis of the results of a large number of tests carried out to determine the acceptability to a large number of observers, of a number of photographs, for which the exposure was known, obtained under various conditions of subject manner and over a range of luminances.

In practice, the variation of the calibration constants among manufacturers is considerably less than this statement might imply, and values have changed little since the early 1970s.

ISO 2720:1974 recommends a range for $$K$$ of 10.6 to 13.4 with luminance in cd/m2. Two values for $$K$$ are in common use: 12.5 (Canon, Nikon, and Sekonic ) and 14 (Minolta, Kenko, and Pentax); the difference between the two values is approximately $1/undefined$ EV.

The earliest calibration standards were developed for use with wide-angle averaging reflected-light meters (Jones and Condit 1941). Although wide-angle average metering has largely given way to other metering sensitivity patterns (e.g., spot, center-weighted, and multi-segment), the values for $$K$$ determined for wide-angle averaging meters have remained.

The incident-light calibration constant depends on the type of light receptor. Two receptor types are common: flat (cosine-responding) and hemispherical (cardioid-responding). With a flat receptor, ISO 2720:1974 recommends a range for $$C$$ of 240 to 400 with illuminance in lux; a value of 250 is commonly used. A flat receptor typically is used for measurement of lighting ratios, for measurement of illuminance, and occasionally, for determining exposure for a flat subject.

For determining practical photographic exposure, a hemispherical receptor has proven more effective. Don Norwood, inventor of incident-light exposure meter with a hemispherical receptor, thought that a sphere was a reasonable representation of a photographic subject. According to his patent (Norwood 1938), the objective was

to provide an exposure meter which is substantially uniformly responsive to light incident upon the photographic subject from practically all directions which would result in the reflection of light to the camera or other photographic register.

and the meter provided for "measurement of the effective illumination obtaining at the position of the subject."

With a hemispherical receptor, ISO 2720:1974 recommends a range for $$C$$ of 320 to 540 with illuminance in lux; in practice, values typically are between 320 (Minolta) and 340 (Sekonic). The relative responses of flat and hemispherical receptors depend upon the number and type of light sources; when each receptor is pointed at a small light source, a hemispherical receptor with $$C$$ = 330 will indicate an exposure approximately 0.40 step greater than that indicated by a flat receptor with $$C$$ = 250. With a slightly revised definition of illuminance, measurements with a hemispherical receptor indicate "effective scene illuminance."

Calibrated reflectance
It is commonly stated that reflected-light meters are calibrated to an 18% reflectance, but the calibration has nothing to do with reflectance, as should be evident from the exposure formulas. However, some notion of reflectance is implied by a comparison of incident- and reflected-light meter calibration.

Combining the reflected-light and incident-light exposure equations and rearranging gives

 * $$\frac {L} {E} = \frac {K} {C}$$

Reflectance $$R$$ is defined as

 * $$R = \frac {\mbox {flux emitted from surface}} {\mbox {flux incident upon surface}}$$

A uniform perfect diffuser (one following Lambert's cosine law) of luminance $$L$$ emits a flux density of $$\pi$$$$L$$; reflectance then is

 * $$R = \frac {\pi L} {E} = \frac {\pi K} {C}$$

Illuminance is measured with a flat receptor. It is straightforward to compare an incident-light measurement using a flat receptor with a reflected-light measurement of a uniformly illuminated flat surface of constant reflectance. Using values of 12.5 for $$K$$ and 250 for $$C$$ gives

 * $$R = \frac {\pi \times 12.5} {250} \approx 15.7\%$$

With a $$K$$ of 14, the reflectance would be 17.6%, close to that of a standard 18% neutral test card. In theory, an incident-light measurement should agree with a reflected-light measurement of a test card of suitable reflectance that is perpendicular to the direction to the meter. However, a test card seldom is a uniform diffuser, so incident- and reflected-light measurements might differ slightly.

In a typical scene, many elements are not flat and are at various orientations to the camera, so that for practical photography, a hemispherical receptor usually has proven more effective for determining exposure. Using values of 12.5 for $$K$$ and 330 for $$C$$ gives

 * $$R = \frac {\pi \times 12.5} {330} \approx 11.9\%$$

With a slightly revised definition of reflectance, this result can be taken as indicating that the average scene reflectance is approximately 12%. A typical scene includes shaded areas as well as areas that receive direct illumination, and a wide-angle averaging reflected-light meter responds to these differences in illumination as well as differing reflectances of various scene elements. Average scene reflectance then would be

 * $$\mbox{average scene reflectance} =

\frac {\mbox {average scene luminance} } {\mbox {effective scene illuminance }} $$

where "effective scene illuminance" is that measured by a meter with a hemispherical receptor.

ISO 2720:1974 calls for reflected-light calibration to be measured by aiming the receptor at a transilluminated diffuse surface, and for incident-light calibration to be measured by aiming the receptor at a point source in a darkened room. For a perfectly diffusing test card and perfectly diffusing flat receptor, the comparison between a reflected-light measurement and an incident-light measurement is valid for any position of the light source. However, the response of a hemispherical receptor to an off-axis light source is approximately that of a cardioid rather than a cosine, so the 12% "reflectance" determined for an incident-light meter with a hemispherical receptor is valid only when the light source is on the receptor axis.

Cameras with internal meters
Calibration of cameras with internal meters is covered by ISO 2721:1982; nonetheless, many manufacturers specify (though seldom state) exposure calibration in terms of $$K$$, and many calibration instruments (e.g., Kyoritsu-Arrowin multi-function camera testers ) use the specified $$K$$ to set the test parameters.

Exposure determination with a neutral test card
If a scene differs considerably from a statistically average scene, a wide-angle averaging reflected-light measurement may not indicate the correct exposure. To simulate an average scene, a substitute measurement sometimes is made of a neutral test card, or gray card.

At best, a flat card is an approximation to a three-dimensional scene, and measurement of a test card may lead to underexposure unless adjustment is made. The instructions for a Kodak neutral test card recommend that the indicated exposure be increased by $1/undefined$ step for a frontlighted scene in sunlight. The instructions also recommend that the test card be held vertically and faced in a direction midway between the Sun and the camera; similar directions are also given in the Kodak Professional Photoguide. The combination of exposure increase and the card orientation gives recommended exposures that are reasonably close to those given by an incident-light meter with a hemispherical receptor when metering with an off-axis light source.

In practice, additional complications may arise. Many neutral test cards are far from perfectly diffuse reflectors, and specular reflections can cause increased reflected-light meter readings that, if followed, would result in underexposure. It is possible that the neutral test card instructions include a correction for specular reflections.

Use in illumination
Light meters or light detectors are also used in illumination. Their purpose is to measure the illumination level in the interior and to switch off or reduce the output level of luminaires. This can greatly reduce the energy burden of the building by significantly increasing the efficiency of its lighting system. It is therefore recommended to use light meters in lighting systems, especially in rooms where one cannot expect users to pay attention to manually switching off the lights. Examples include hallways, stairs, and big halls.

There are, however, significant obstacles to overcome in order to achieve a successful implementation of light meters in lighting systems, of which user acceptance is by far the most formidable. Unexpected or too frequent switching and too bright or too dark rooms are very annoying and disturbing for users of the rooms. Therefore, different switching algorithms have been developed:
 * difference algorithm, where lights are switched on at a lower light level than they switch off, thus taking ensuring the difference between the light level of the 'on' state and 'off' state is not too big
 * time delay algorithms:
 * a certain amount of time must pass since the last switch
 * a certain amount of time at a sufficient illumination level must pass.

Other uses
In Scientific Research & Development uses, a light meter consists of a radiometer (the electronics/readout), a photo-diode or sensor (generates an output when exposed to electromagnetic radiation/light) a filter (used to modify the incoming light so only the desired portion of incoming radiation reaches the sensor) and a cosine correcting input optic (assures the sensor can see the light coming in from all directions accurately).

When the word light meter or photometer is used in place of radiometer or optometer, or it is often assumed the system was configured to see only visible light. Visible light sensors are often called illuminance or photometric sensors because they have been filtered to be sensitive only to 400-700 nanometers (nm) mimicking the human eyes' sensitivity to light. How accurately the meter measures often depends on how well the filtration matches the human eyes' response.

The sensor will send a signal to the meter that is proportional to the amount of light that reaches the sensor after being collected by the optics and passing through the filter. The meter then converts the incoming signal (typically current or voltage) from the sensor into a reading of calibrated units such as Foot-Candles (fc) or Lux (lm/m^2). Calibration in fc or lux, is the second most important feature of a light meter. It not only converts the signal from V or mA, but it also provides accuracy and unit to unit repeatability. National Institute of Standards and Technology (NIST) traceability and ISO/IEC 17025 accreditation are two well known terms that verify the system includes a valid calibration.

The meter/radiometer/photometer portion may have many features including:

Zero: subtracts ambient/background light levels, or stabilize the meter to the working environment

Hold: freezes the value on the display.

Range: for systems that are not linear and auto ranging this function allows the user to select the portion of the meter electronics that best handles the signal level in use.

Units: For illuminance the units are typically only lux and foot-candles but many light meters can also be used for UV, VIS and IR applications so the readout could change to W/cm^2, candela, Watts etc.

Integrate: sums up the values into a dose or exposure level i.e. lux*sec or J/cm^2. Along with having a variety of features, a light meter may also be usable for a variety of applications. These may include the measurement of other bands of light such UVA, UVB, UVC and Near IR. For example, UVA and UVB light meters are used for phototherapy or treatment of skin conditions, germicidal radiometers are used for measuring the UVC level from lamps used for disinfection and sterilization, luminance meters are used to measure the brightness of a sign, display or exit sign, PAR quantum sensors are used to measure how much of a given light source's emission will help plants grow, and UV-curing radiometers test how much of the lights emission is effective for hardening a glue, plastic, or protective coating. Some light meters also have the ability to provide a readout in many different units. Lux and footcandles are the common units for visible light, but so are Candelas, Lumens, and Candela per square meter. In the realm of disinfection, UVC is typically measured in watts per square centimeter, or watts for a given individual lamp assembly, whereas systems used in the context of the curing of coatings often provide readouts in Joules per Square centimeter. Regular measurements of UVC light intensity thus can serve to provide assurance of proper disinfection of water and food-preparation surfaces, or reliable coating hardness in painted products. Although a light meter can take the form of a very simple handheld tool with one-button operation, there are also many advanced light-measurement systems available for use in numerous different applications. These can be incorporated into automated systems that can, for example, wipe lamps clean when a certain reduction in output is detected, or that can trigger an alarm when lamp-failure occurs.

title: Light meter


text:
Printer point

In photography, a printer point is a unit of relative exposure, in printing a negative, equal to a 1/12 of a stop or 0.025 Log(base 10) unit (one-fortieth of a decade) of exposure ratio.

This numbering scheme is used in photographic printing and photographic filters. Printer points were also used to specify color timing for photochemical film processing, particularly for motion pictures shot on film.

Increasing or decreasing the light by twelve points increases or decreases the exposure by a factor of two. Such adjustments are used for darkness and color adjustment in photographic enlargers, for example. A one-stop change in the exposure of a negative may require only an adjustment of about 6 to 8 printer points in printing, depending on the gamma of the film.

title: Printer point