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| [[Image:Chromatic abberation lens diagram.svg|thumb|right|Chromatic aberration of a single lens causes different wavelengths of light to have differing focal lengths.]]
| | The initially popular kind are the creams and ointments where you rub a medicine onto the outside of the rectum. It intends to treat a hemorrhoid by relaxing the blood vessels. This relaxes the cells so that it no longer continues to bulge. Once the tissues go down, the hemorrhoids may not flare up as much. This is wonderful for a small temporary relief, nevertheless the hemorrhoid will usually flare up again when utilizing this system of main treatment.<br><br>Before we finally discover out the number one [http://hemorrhoidtreatmentfix.com/hemorrhoid-symptoms hemorrhoid symptoms], it is significant to learn first the cause of the hemorrhoid. Actually there are many causes of hemorrhoid including irregularity, prolong sitting or standing, pregnancy along with a lot more. The initially thing which you have to do is to remedy the cause plus for sure getting rid of your hemorrhoid can follow.<br><br>Drink plenty of water. Regarding 8 - 10 glasses of water a day. This is to kind of keep the stool soft thus it doesn't ruture any viens and result bleeding throughout a bowel movement.<br><br>If you find going to the bathroom for a bowel movement truly difficult think about a stool softener. These could work truly well and reduce the need for straining. These is purchased conveniently over the counter and is highly efficient. If you would like something a little more natural you might like to consider eating prunes or drinking prune juice.<br><br>Witch Hazel when used as an component in hemorrhoid treatments has an almost magical impact. If you empty a small bottle of Witch Hazel into the bathroom tissue box, the tissue will absorb it. This makes a surprisingly soothing replace for coarser toilet tissue plus is superb for gentle cleansing of the delicate area in addition to reducing pain plus itching.<br><br>Three. The upcoming internal hemorrhoids treatment that we may employ that might help you with a piles is to add a peeled garlic clove into a rectum. The garlic might help you eliminate the hemorrhoid.<br><br>When using a sitz bath tub, you can use specialized soaps plus lotions that is made to be employ with all the bath. This can aid treat different symptoms of the hemorrhoids, also. You are able to pick up any sitz tub at the surrounding wellness retailer or we can buy 1 online. |
| [[File:Lens6b-en.svg|thumb|right|An '''achromatic doublet''' brings red and blue light to the same focus, and is the earliest example of an achromatic lens.]]
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| [[File:Achromatic focal curve.svg|thumb|right|In an achromatic lens, two wavelengths are brought into the same focus, here red and blue.]]
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| An '''achromatic lens''' or '''achromat''' is a [[lens (optics)|lens]] that is designed to limit the effects of [[chromatic aberration|chromatic]] and [[spherical aberration]]. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus in the same plane.
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| The most common type of achromat is the '''achromatic [[Doublet (lens)|doublet]]''', which is composed of two individual lenses made from [[glass]]es with different amounts of [[Dispersion (optics)|dispersion]]. Typically, one element is a negative ([[Lens (optics)#Types of simple lenses|concave]]) element made out of [[flint glass]] such as F2, which has relatively high dispersion, and the other is a positive ([[Lens (optics)#Types of simple lenses|convex]]) element made of [[Crown glass (optics)|crown glass]] such as BK7, which has lower dispersion. The lens elements are mounted next to each other, often cemented together, and shaped so that the chromatic aberration of one is counterbalanced by that of the other.
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| In the most common type (shown), the positive [[Optical power|power]] of the crown lens element is not quite equalled by the negative power of the flint lens element. Together they form a weak positive lens that will bring two different [[wavelength]]s of light to a common [[focus (optics)|focus]]. Negative doublets, in which the negative-power element predominates, are also made.
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| ==History==
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| Theoretical considerations of the feasibility of correcting chromatic aberration were debated in the 18th century following [[Isaac Newton|Newton]]'s statement that such a correction was impossible (see [[History of the telescope#Achromatic refracting telescopes|History of the telescope]]). Credit for the invention of the first achromatic doublet is often given to an English [[barrister]] and amateur optician named [[Chester Moore Hall]].<ref name="daumas">Daumas, Maurice, ''Scientific Instruments of the Seventeenth and Eighteenth Centuries and Their Makers'', Portman Books, London 1989 ISBN 978-0-7134-0727-3</ref><ref name=Stargazer>{{cite book |url=http://books.google.com/books?id=2LZZginzib4C&pg=PA140 |title=Stargazer: the life and times of the telescope |first=Fred |last=Watson |publisher=Allen & Unwin |year=2007 |pages=140–55 |isbn=978-1-74175-383-7}}</ref> Hall wished to keep his work on the achromatic lenses a secret and contracted the manufacture of the [[Crown glass (optics)|crown]] and [[flint glass|flint]] lenses to two different opticians, Edward Scarlett and James Mann.<ref>Fred Hoyle, ''Astronomy; A history of man's investigation of the universe'', Rathbone Books, 1962, LC 62-14108</ref><ref>{{cite web |url=http://www.mhs.ox.ac.uk/sphaera/index.htm?issue8/articl5 |title=Sphaera—Peter Dollond answers Jesse Ramsden |accessdate=July 31, 2009}} A review of the events of the invention of the achromatic doublet with emphasis on the roles of Hall, Bass, John Dollond and others.</ref><ref>{{cite book |title=Techniques in microscopy for biomedical applications |first1=Terje |last1=Dokland |first2=Mary Mah-Lee |last2=Ng |page=23 |year=2006 |isbn=981-256-434-9 |url=http://books.google.com/books?id=Ix3G9_Rr0EAC&pg=PA23&lpg=PA23&dq=achromatic+lens+subcontract#v=onepage&q=&f=false |accessdate=July 31, 2009}}</ref> They in turn sub-contracted the work to the same person, [[George Bass (optician)|George Bass]]. He realized the two components were for the same client and, after fitting the two parts together, noted the achromatic properties. Hall failed to appreciate the importance of his invention, and it remained known to only a few opticians.
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| In the late 1750s, Bass mentioned Hall's lenses to [[John Dollond]], who understood their potential and was able to reproduce their design.<ref name=Stargazer/> Dollond applied for and was granted a patent on the technology in 1758, which led to bitter fights with other opticians over the right to make and sell achromatic doublets.
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| Dollond's son [[Peter Dollond|Peter]] invented the [[apochromat]], an improvement on the achromat, in 1763.<ref name=Stargazer/>
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| ==Types==
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| Several different types of achromat have been devised. They differ in the shape of the included lens elements as well as in the optical properties of their glass (most notably in their [[optical dispersion]] or [[Abbe number]]).
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| In the following, 'R' denotes the [[radius]] of the [[sphere]]s that define the optically relevant [[refraction|refracting]] lens surfaces. By convention, R<sub>1</sub> denotes the first lens surface counted from the object. A doublet lens has four surfaces with radii R<sub>1</sub> to R<sub>4</sub>.
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| ===Littrow doublet===
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| Uses an equiconvex crown glass lens with R<sub>1</sub>=R<sub>2</sub>, and a second flint glass lens with R<sub>3</sub>=-R<sub>2</sub>. The back of the flint glass lens is flat. A Littrow doublet can produce a ghost image between R<sub>2</sub> and R<sub>3</sub> because the lens surfaces of the two lenses have the same radii. It may also produce a ghost image between the flat R<sub>4</sub> surface and rear of the telescope tube.
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| ===Fraunhofer doublet (Fraunhofer objective)===
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| The first lens has positive refractive power, the second negative. R<sub>1</sub> is set greater than R<sub>2</sub>, and R<sub>2</sub> is set close to, but not equal to, R<sub>3</sub>. R<sub>4</sub> is usually greater than R<sub>3</sub>. In a Fraunhofer doublet, the dissimilar curvatures of R<sub>2</sub> and R<sub>3</sub> are mounted close, but not in contact.<ref>[http://books.google.com/books?id=0xxV3zbafeYC&pg=PA38&dq=Fraunhofer+dialyte&hl=en&ei=-JkHTYniEYH-8Aax9tjwDA&sa=X&oi=book_result&ct=result&resnum=8&ved=0CEQQ6AEwBw#v=onepage&q=Fraunhofer%20dialyte&f=false William L. Wolfe, Optics made clear: the nature of light and how we use it, page 38]</ref> This design yields more degrees of freedom (one more free radius, length of the air space) to correct for [[optical aberration]]s.
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| ===Clark doublet===
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| Uses an equiconvex crown with R<sub>1</sub>=R<sub>2</sub>, and a flint with R<sub>3</sub>≃R<sub>2</sub> and R<sub>4</sub>≫R<sub>3</sub>. R<sub>3</sub> is set slightly shorter than R<sub>2</sub> to create a focus mismatch between R<sub>2</sub> and R<sub>3</sub>, thereby reducing ghosting between the crown and flint.
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| ===Oil-spaced doublet===
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| The use of oil between the crown and flint eliminates the effect of ghosting, particularly where R<sub>2</sub>=R<sub>3</sub>. It can also increase light transmission slightly and reduce the impact of errors in R<sub>2</sub> and R<sub>3</sub>.
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| ===Steinheil doublet===
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| The Steinheil doublet, devised by [[Carl August von Steinheil]], is a flint-first doublet. In contrast to the Fraunhofer doublet, it has a negative lens first followed by a positive lens. It needs stronger curvature than the Fraunhofer doublet.<ref>Kidger, M.J. (2002) Fundamental Optical Design. SPIE Press, Bellingham, WA, pp. 174ff</ref> | |
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| ===Dialyte===
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| [[Dialyte lens]]es have a wide air space between the two elements. They were originally devised in the 19th century to allow much smaller flint glass elements down stream since flint glass was hard to produce and expensive.<ref>[http://books.google.com/books?id=p282ijnF3C0C&pg=PA55&lpg=PA55&dq=dialyte+lens+telescope&source=bl&ots=ukPf6xKIDW&sig=WWZdN_FqeR4OElFXFhDdUH6z7Iw&hl=en&ei=zWz8S5r9OYH7lwff05TfDw&sa=X&oi=book_result&ct=result&resnum=8&ved=0CC4Q6AEwBzgK#v=onepage&q=dialyte%20lens%20telescope&f=false Peter L. Manly, Unusual Telescopes, page 55]</ref> They are also lenses where R<sub>2</sub> and R<sub>3</sub> can not be cemented because they have dissimilar curvatures.<ref>Fred A. Carson, Basic optics and optical instruments, page AJ-4</ref>
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| ==Design==
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| The first-order design of an achromat involves choosing the overall power <math>\phi_{\text{sys}}</math> of the doublet and the two glasses to use. The choice of glass gives the mean refractive index, often written as <math>n_d</math> (for the refractive index at the [[Fraunhofer]] [[Abbe number|"d" spectral line wavelength]]), and the [[Abbe number]] <math>V</math> (for the reciprocal of the glass [[dispersion (optics)|dispersion]]). To make the linear dispersion of the system zero, the system must satisfy the equations
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| :<math>\begin{align} \phi_1 + \phi_2 &= \phi_{\text{sys}} \\ \frac{\phi_1}{V_1} + \frac{\phi_2}{V_2} &= 0 \ ,\end{align}</math>
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| where the [[optical power|lens power]] is <math>\phi = 1/f</math> for a lens with [[focal length]] <math>f</math>. Solving these two equations for <math>\phi_1</math> and <math>\phi_2</math> gives
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| :<math>\frac{\phi_1}{\phi_{\text{sys}}} = \frac{V_1}{V_1 - V_2} \qquad \text{and} \qquad \frac{\phi_2}{\phi_{\text{sys}}} = \frac{-V_2}{V_1 - V_2} \ .</math>
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| Since <math>\phi_2 = -\phi_1 V_2 / V_1</math>, and the [[Abbe number]]s are positive-valued, the power of the second element in the doublet is negative when the first element is positive.
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| ==See also==
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| {{Comparison_chromatic_focus_shift_plots.svg}}
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| * [[Achromatic telescope]]
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| * [[Superachromat]]
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| ==References==
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| {{reflist|30em}}
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| [[Category:Lenses]]
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The initially popular kind are the creams and ointments where you rub a medicine onto the outside of the rectum. It intends to treat a hemorrhoid by relaxing the blood vessels. This relaxes the cells so that it no longer continues to bulge. Once the tissues go down, the hemorrhoids may not flare up as much. This is wonderful for a small temporary relief, nevertheless the hemorrhoid will usually flare up again when utilizing this system of main treatment.
Before we finally discover out the number one hemorrhoid symptoms, it is significant to learn first the cause of the hemorrhoid. Actually there are many causes of hemorrhoid including irregularity, prolong sitting or standing, pregnancy along with a lot more. The initially thing which you have to do is to remedy the cause plus for sure getting rid of your hemorrhoid can follow.
Drink plenty of water. Regarding 8 - 10 glasses of water a day. This is to kind of keep the stool soft thus it doesn't ruture any viens and result bleeding throughout a bowel movement.
If you find going to the bathroom for a bowel movement truly difficult think about a stool softener. These could work truly well and reduce the need for straining. These is purchased conveniently over the counter and is highly efficient. If you would like something a little more natural you might like to consider eating prunes or drinking prune juice.
Witch Hazel when used as an component in hemorrhoid treatments has an almost magical impact. If you empty a small bottle of Witch Hazel into the bathroom tissue box, the tissue will absorb it. This makes a surprisingly soothing replace for coarser toilet tissue plus is superb for gentle cleansing of the delicate area in addition to reducing pain plus itching.
Three. The upcoming internal hemorrhoids treatment that we may employ that might help you with a piles is to add a peeled garlic clove into a rectum. The garlic might help you eliminate the hemorrhoid.
When using a sitz bath tub, you can use specialized soaps plus lotions that is made to be employ with all the bath. This can aid treat different symptoms of the hemorrhoids, also. You are able to pick up any sitz tub at the surrounding wellness retailer or we can buy 1 online.