. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. ugh a new one wasmade with the recess for the plate at least double theusual depth. The screen was then placed in, and astrip of cardboard introduced round the margin so as toprevent the plate touching. Theground-glass had, of course, to becorrespondingly set back in thefocussing frame to agree with theposition of the sensitive plate. Anobvious disadvantage of this methodwas that any alteration of the screendistance, by putting in thicker card-board strips, would put the plateout of focus, u
. The half-tone process. A practical manual of photo-engraving in half-tone on zinc, copper, and brass. ugh a new one wasmade with the recess for the plate at least double theusual depth. The screen was then placed in, and astrip of cardboard introduced round the margin so as toprevent the plate touching. Theground-glass had, of course, to becorrespondingly set back in thefocussing frame to agree with theposition of the sensitive plate. Anobvious disadvantage of this methodwas that any alteration of the screendistance, by putting in thicker card-board strips, would put the plateout of focus, unless the ground-glasswas correspondingly altered. This difficulty was overcome bydividing the plate recess into twoportions, as in the case of the doubleback of an ordinary camera. Thedivision was effected by means of a thin silver plate orwire placed diagonally across the corners (fig. n).The sensitive plate was then laid on one side of thedivision and the screen on the other, springs generallybeing provided to prevent the screen falling out. Ifany alteration of the screen distance was required a. Fig. II. A—Framework of dark slide. B—Back lid of dark slide. C—Plate carrier. D— Wire corner. E—Cardboard separation. F—Screen carrier. G—Spring. H—Shutter. THE STUDIO. 43 piece of cardboard could be laid between the screenand the corner wires. Different sizes of screens can, ofcourse, be placed in carriers in the same way as theplates. Screens are usually T\in. thick, and in makinga dark slide it is well to allow twice this depth forthe screen carrier, so that an adjustment up to xVn-may be obtained by the insertion of thicknesses ofcardboard. It is better that the latter should be cutout like the mask of a lantern slide and the thicknessa definite fraction of an inch, say ^in. or ^in., sothat the combination of any number of these wouldgive any pre-determined screen distance, which could,moreover, be accurately repeated at any time. A dark slide arranged on the fo
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Keywords: ., bookcentury1900, bookdecade1900, bookidhalftoneproc, bookyear1904
