[vevuze] SCREEN IN THE PHOTO-MECHANICAL PROCESS AS 
being one-quarter of the whole aperture. But we now have a resource 
which was not available with the cross-lined screen: we can change 
the shape of the aperture. Fig. 21 represents a diaphragm producing 
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the effect of a cross-lined screen in which the transparent lines are double 
the width of the opaque lines. The dimensions are : 
7 
AB = 35 4. 
25 
Op = ga: 
i 
The dots of this diaphragm are given in Fig, 22; a comparison with 
Fig. 18 shows a very great improvement. The light tones are fairly trans- 
lated ; the dots are only a trifle too small, but the gradation is good. 
The light shadows are not quite so good, but much better than with the 
cross-lined screen ; there is no improvement in the deep shadows. This 
diaphragm requires two and one-half times the exposure of the square 
diaphragm. Its rapidity may be increased by making the arms of the 
inner star less pointed and increasing proportionately the width, HF 
(Fig. 21), of the extensions, but that makes all the black dots smaller 
and the print less perfect. It is quite easy to devise other shapes of dia- 
phragms. One is given in Fig, 27 ; the apertures are not so elongated as 
in Fig. 21, butit has the drawback of requiring very accurate adjustment. 
