Editing Daguerreotype (section)

== Reduction of exposure time ==
In the early 1840s, two innovations were introduced that dramatically shortened the required exposure times: a lens that produced a much brighter image in the camera, and a modification of the chemistry used to sensitize the plate.

The first daguerreotype cameras could not be used for portraiture, as the exposure time required would have been too long. The cameras were fitted with Chevalier [[Camera lens#Early photographic camera lenses|lenses]] which were "[[Lens speed|slow]]" (about [[F-number|f/14]]).{{NoteTag|Parisian optician Charles Chevalier had long been making assorted high-quality lenses for microscopes, telescopes and other optical devices. The "Chevalier lens" referred to in the context of these earliest photographic cameras was an 81&nbsp;mm diameter [[Lens (optics)#Types of simple lenses|meniscus]] [[Achromatic lens|achromatic doublet]], mounted with its concave surface forward, and had a [[focal length]] of about 380&nbsp;mm (each was ground and polished by hand, so the exact focal length of each was slightly different). A [[diaphragm (optics)|diaphragm]] with a fixed 27&nbsp;mm diameter opening formed the front end of the lens barrel and was spaced away from the lens at a distance that optimally reduced the most important [[Lens (optics)#Aberrations|lens aberrations]]. Chevalier soon began producing other, faster camera lens designs which are also commonly called "Chevalier lenses", a potential source of confusion.}} They projected a sharp and undistorted but dim image onto the plate. Such a lens was necessary in order to produce the highly detailed results which had elicited so much astonishment and praise when daguerreotypes were first exhibited, results which the purchasers of daguerreotype equipment expected to achieve. Using this lens and the original sensitizing method, an exposure of several minutes was required to photograph even a very brightly sunlit scene. A much "faster" lens could have been provided—simply omitting the integral fixed [[Diaphragm (optics)|diaphragm]] from the Chevalier lens would have increased its working aperture to about [[F-number|f/4.7]] and reduced the exposure time by nearly 90 percent—but because of the existing state of lens design the much shorter exposure would have been at the cost of a peripherally distorted and very much less clear image. With uncommon exceptions, daguerreotypes made before 1841 were of static subjects such as landscapes, buildings, monuments, statuary, and [[Still life photography|still life]] arrangements. Attempts at [[portrait photography]] with the Chevalier lens required the sitter to face into the sun for several minutes while trying to remain motionless and look pleasant, usually producing repulsive and unflattering results. The Woolcott mirror lens that produced tiny, postage stamp size daguerreotypes made portraiture with the daguerreotype process possible and these were the first photographic portraits to be produced. In 1841, the [[Petzval lens|Petzval Portrait Lens]] was introduced.<ref>The story of the development of the Petzval Portrait lens is given in {{harv|Eder|1978|pp=291–313}}</ref><ref>{{cite book |last=Kingslake |first=Rudolph |author-link=Rudolf Kingslake |year=1989 |title=A History of the Photographic Lens |url=https://books.google.com/books?id=OJrJrEJ-r9QC&pg=PA35 |publisher=Academic Press |page=35 |isbn=978-0-12-408640-1}}</ref><ref>[https://www.lensrentals.com/blog/2010/10/from-petzvals-sum-to-abbes-number/ ''From Petzval's Sum to Abbe's Number'' Roger Cicala]</ref> Professor [[Andreas von Ettingshausen]] brought the need for a faster lens for daguerreotype cameras to his colleague, Professor Petzval's attention, who went ahead in cooperation with the [[Voigtländer]] firm to design a lens that would reduce the time needed to expose daguerreotype plates for portraiture. Petzval was not aware of the scale of his invention at the start of his work on the lens, and later regretted not having secured his rights by obtaining letters patent on his invention. It was the first lens to be designed using mathematical computation, and a team of mathematicians whose specialty was in fact calculating the trajectories of ballistics was put at Petzval's disposal by the [[Archduke Louis of Austria|Archduke Ludwig]]. It was scientifically designed and optimized for its purpose. With a working aperture of about [[F-number|f/3.6]], an exposure only about one-fifteenth as long as that required when using a Chevalier lens was sufficient. Although it produced an acceptably sharp image in the central area of the plate, where the sitter's face was likely to be, the image quality dropped off toward the edges, so for this and other reasons it was unsuitable for landscape photography and not a general replacement for Chevalier-type lenses. Petzval intended his lens to be convertible with two alternative rear components: one for portraiture and the other for landscape and architecture.<ref>[https://monoskop.org/images/b/b6/Kingslake_Rudolf_1955_The_Orthoscopic_Lens.pdf The Orthoscopic Lens]</ref>[[File:Gezicht op de Predikherenlei en -brug te Gent, ca. 1839, STAM Gent.tif|thumb|‘View of the Predikherenlei and Predikherenbrug’ depicts the first photographic record of [[Ghent]] and in all probability [[Belgium]]. It dates back to October 1839, when optician François Braga arrived in [[Ghent]] with the daguerreotype camera. Together with his friend, seller of prints and engravings Joseph Pelizzaro, he took the picture on the second floor of judge Philippe Van de Velde’s residence on the Ajuinlei. Of the four original plates they made, two plates are in the holdings of STAM – [[Ghent City Museum]], while the two others are lost. ]]

The other major innovation was a chemical one. In Daguerre's original process, the plate was sensitized by exposure to [[iodine]] fumes alone. A breakthrough came with the discovery that when exposure to [[bromine]] or [[chlorine]] fumes was correctly combined with this, the sensitivity of the plate could be greatly increased, which in turn greatly reduced the required exposure time to between fifteen and thirty seconds in favorable lighting conditions, according to Eder.<ref>{{harv|Eder|1978|pp=265,293}}</ref> Several experimenters discovered the propensity of using chlorine and bromine in addition to iodine:<ref>{{cite book |last=Newhall |first=Beaumont |year=1976 |orig-year=First published 1961 |title=The Daguerreotype in America |url=https://books.google.com/books?id=Gp0fPG7UcXwC&pg=PA122 |edition=3rd |publisher=Dover Publications |page=122 |isbn=0-486-23322-7 }}</ref> Wolcott, whose "Wolcott's mixture" was marketed by his partner, John Johnson that they called "quickstuff"; two unrelated individuals with the surname Goddard – Philadelphia physician and chemist [[Paul Beck Goddard]],<ref>[http://historiccamera.com/cgi-bin/librarium2/pm.cgi?action=app_display&app=datasheet&app_id=2405& Paul Beck Goddard]</ref> and [[John Frederick Goddard]] who lectured at the Adelaide Gallery before assisting Beard with setting up the first daguerreotype portraiture studio on the roof of the Regent Street Polytechnic;<ref>[http://www.historiccamera.com/cgi-bin/librarium/pm.cgi?action=display&login=richardbeard ''Historic Camera'' Richard Beard]</ref><ref>[https://books.google.com/books?id=yVFdAgAAQBAJ&pg=PA595 John Frederick Goddard]</ref> (John Frederick Goddard was the first to publish information that bromine increased the sensitivity of daguerreotype plates in the ''Literary Gazette'' of 12 December 1840)<ref name="BargerWhite2000">{{cite book |last1=Barger |first1=M. Susan |last2=White |first2=William B. |year=2000 |title=The Daguerreotype: Nineteenth-Century Technology and Modern Science |url=https://books.google.com/books?id=FLTyvuWX6MMC&pg=PA34 |publisher=JHU Press |pages=34– |isbn=978-0-8018-6458-2 }}</ref><ref>[http://www.daguerreotypearchive.org/texts/P8400004_GODDARD_LIT_GAZETTE_1840-12-12.pdf ''Literary Gazette'' 12 December 1840]</ref><ref>[http://www.daguerreotypearchive.org/texts/P8630001_HUGHES_BRIT_JOURN_PHOTOG_1863-12-15.pdf ''The British Journal of Photography'' 15 December 1863 Jabez Hughes ''The Discoverer of the Use of Bromine in Photography: a Few Facts and an Appeal'']</ref> and in Vienna: Krachowila and the [[Johann August Natterer|Natterer]] brothers.