. The book of photography; practical, theoretical and applied. ismarked to give the required density inopacity logarithms. This arrangement isobviously available for a number ofdifferent pui-poses besides that for whichit is primarily intended; for example,the estimation of exposures in bromideprinting, etc. Finding Actinogeaph Speed of Plate. The exposure to be given in the cameracan easily be found by means of the going paragraphs, filled a long-felt want,and it has been of great use both to themakers and the users of plates. It is atonce both scientific and practical, theunit or candlemeter
. The book of photography; practical, theoretical and applied. ismarked to give the required density inopacity logarithms. This arrangement isobviously available for a number ofdifferent pui-poses besides that for whichit is primarily intended; for example,the estimation of exposures in bromideprinting, etc. Finding Actinogeaph Speed of Plate. The exposure to be given in the cameracan easily be found by means of the going paragraphs, filled a long-felt want,and it has been of great use both to themakers and the users of plates. It is atonce both scientific and practical, theunit or candlemeter second being the besthitherto proposed, and one which can atany time be produced. The inertia of aplate having been measui-ed as described,it is possible to so time the exposures inthe camera as to get densities which aredirectly proportional to the logarithms ofthe intensities of the light which producesthem, and thus to produce negativeswhich are as nearly as possible density obtained in any particular ex-periment is dependent upon the time of. Fig. .566.—The Chapman Jones Opacity Meter. Hurter and Driffield Actinograph whenthe inertia of the plate is known. Theactinograph speed of the plate isobtained by means of the formula s =34/i, when s is the speed of the plate andi the inertia. For instance, the speed ofthe Ilford plates is as follows :^ Speed. Ilford ordinaryIlford rapid 341-4 = — = 17 = ^^= 24 34 Ilford special rapid ^^-^— ^^056 60 Concluding Remarks. The method of measuring the speed of aphotographic plate, described in the fore- exposure as well as upon the action oflight. During development the growthof density is rapid at first, but it gradu-ally slows down, and finally comes to astandstill; the subsequent reductionbeing due to the chemical action of thedeveloper upon the unaltered silverbromide, and being really fog, in no wayalters the ratios of the densities, thoughit may lead to a certain amount of ex-aggeration in the appearance of a nega-
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectphotography, bookyear
