The positive process in photography

Abstract

II'IIIS"lcr&SSITY Olt 'rll I. : ~i~:~~~r i v i~: -l~~s l~~I \~l~1'itock:ss SiiIts o i si~vcr owe t~icir iiiiriviillcntl positioii iis the hnqis of so iiiniiy @mtogriipliic ~~roccsscs to tlic two properties of high sciisitivity to liglit, iiiiil ciisc Of coiivcrsioii into vcry StiiIJlc iiisoliil~lc t1criviit.ivcs. 'i'litw cbrivi~tivcs, of wliicli tlic iiict.iil iiiitl tlic siilpliitlc :ire tlic iiiost iinportiiiit csniitlilcs, iirc dark i i i COIOIIP, iiiitl iiiidcr ortliiiiiry coiiditioiis tlic qiiniititics ~)ro'odiiccd iucrcnsc progrcssivcly with iiicrciisiug light nctiou. For tlicsc rcnsoiis, tlic I~riglitcr tlic light fiilliiig oil it portion of i b iiintcrinl tluriitg csposurc, t,lic blrickcr will bc the deposit, uiid Iiciicc t,lic single ol~criitioii .of ~XIWSIICC, dcvclopinciit, ciud fisiitioii of a silver hnlidc cniiilsion iiiiist protliicc n iicgiitivc iiiinge of iiii ol~jcct, iind thc production of ii p~sitivc iiiiiigc iiiust i i c~c~~i i r i l y com[)risc thc two proccsst!~ of t,lic foriii:ition ot ii iiogiitivc iiungc, iiiid tlic production froiii it of i i jiositive iitiiigo (is., a iicgiitivc of tlic iicgiitivc). Tlic tliscovcry of II stnhlc wliitc tlcriviitivc of silver woiiltl itiiikc it possiblc to produce it dircct positive result wlicii viewed by reflected light, by the proccss of contiiig ii sciisitivc cniulsioii on n bliick support rind coiivcrtiiig tlic csposcd sciisibivo silver coiiipoiiiid iiito the wliitc iiisoliible dcririit,ivc. Agiiiii, it siiiiplc iiictliotl of tlevclopiiig the iiiicsposctl portion of t.hc silver iitiiigc iiistcnd of the c s p s c d portioii would ~iro(Iiicc t i dircct positive, hut iiiitil soiiic siicli ndviiiicc iis t,liis I i i i~ becu iiiiidc, the nc~itivc-positive proecss iiiust coiitiiiuc to bc nliiiost iiuivctrsitlly used.The pvsitice upowrc.-A positive is olitiiiiicd f r w i ii negiit ivc liy csposiiig sciisit.ivc iiiiitcriiil in coiitiict with t,lic coiitcd side of tlic iicgiitivc, or by cxposiiig it iii R positioii coiiicidciit with thc rcnl iiiiiigc of tlic Iiegiit ivo iii soiiic opticril systciii. In citlicr ciiso tlic iicgat ivc is iuiiforiiily illiiiiiiiiiitcd, itiitl light fiills oil thc positivc iiiiitcriiil iittcr traiisiiiissioii by tlic iicgiitivc. All portions of the positive itiittcriiil nrc tliiis csjioscd for tho siiiiic tiiiic, but dilTcrciit portions rcccivc difrcrciit csposiircs, iiccortliiig to tlic viiriirtioiis i n iiitciisity C G U S (~ by dillcrciiccs in opiicitp of corresponding porlioiis of tlic ucgntivc. It lins bccn cspliiiiicd ( C ' i i i . :~~. &S-, h i ) . , 1931, p. 707) thiit density* is iiiciisurcd iis the logirilliiti of thc opncity ; tlmt is, if i i uiiiforiii intensity of 1 iiictrccnudlcs fnlls on tlic negative, the tlciisity Dl \vliicli trnnsinits nil intensity of I, is givcii hy the foriiiiilii : I D, ; = log oliiicity = log-= log Ilog I,. 11If 1, is tlic iiitciiuity trriiisiiiittcd by ii tlciisity 'irud .a,, rc!ccivctl by portioiis of ii psitivc iiiiitcriril oxposcd bcliiiid tlicsc tlciisitics will I)c cquiil to the intcii...