Identifier: halftoneprocessp00verf (find matches)
Title: The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass
Year: 1904 (1900s)
Authors: Verfasser, Julius
Subjects: Photoengraving
Publisher: London, Iliffe & sons, limited
Contributing Library: Getty Research Institute
Digitizing Sponsor: Getty Research Institute

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screw arrangement can beprovided at the side for the purpose of squeezing theboards together when the joined edges open. The size of the board should be at least four timesthe area of the largest plate the camera will take ; inother words, its diagonal should be twice the diagonal 6o THE HALF-TONE PROCESS. of a 15x12 plate if the camera is for that size. As arule the boards in use are fully four times the diagonalof the plate size. A rising and falling movement for the copy-board isnot necessary. A horizontal line coincident with the centre of thelens should bestruck acrossthe board andthe copy pin-ned centrallyon this line.The copy-board shouldbe painted deadblack, as itthenreflectedand is not soconfusing tothe eye whenfocussing. A form ofstand whichhas some ad- Fig. 23. vantages is shown in fig. 23. It can only be used when the lensis fitted with mirror or prism, and the lens mustbe of comparatively short focus, or the stand will haveto be so tall as to be inconvenient. Such a stand
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iight THE STUDIO. 61 takes up little room, and the downward illuminationof the copy is very perfect, copying being done verywell against an ordinary window. It is very useful in copying from open books, or formaking negatives direct from such objects as coins,medals, jewellery, etc. The direct vertical light obviatesall trouble due to grain or surface reflections, ardshadows may be avoided by having a glass plate forsupporting such objects as jewellery, a white reflectorbeing placed underneath at a suitable angle. Next we must decide on the lens, and the essentialpoints to remember are that it must be of the rapidrectilinear type, achromatic, of good covering powerat a large aperture, and of fairly long focus. Singlelandscape lenses, portrait lenses, hand camera lenses,and wide angle lenses must be set aside as unsuitable.It will not be found practicable to use any lens undernine inches focus for the reasons subsequently explained,and even with that length it should not be used forany

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