It would be necessary to use a compensating filter, as in all screen-plate processes, to reduce the vision of the plate to that of the eye, and this could only be done by trial and error, using a white surface as the object and making successive filters and exposures until it was rendered as white.

There are mathematical rules for finding the separation between the cross-lined screen and the sensitive surface, which is dependent on the stop aperture, and the extension of the camera; but the simplest plan is to use a magnifier and examine the image, and so adjust the distance that the colored rectangles or other figures are seen to be sharply defined with distinct edges: this involves a somewhat delicate screw adjustment for the screen, which must necessarily be at the same distance from the sensitive surface at all points. It should be mentioned, in connection with the focusing, that it is impossible to obtain critical sharpness with ground glass, and assuming that the camera is to be used for other work as well, then the only thing to do is to mark a small cross with a hard lead pencil on the center of the ground glass, and cement a microscopic cover glass over this with Canada balsam. This gives a perfectly clear spot on which when focusing with the naked eye nothing but the cross can be seen; but, if a magnifier be used, the image and the cross are easily focused. The magnifier used should be of the type in which the distance from the glass can be adjusted and then fixed once for all, and it should have a sleeve by which the distance from the glass is made permanent for all time. If the lead pencil cross be once sharply focused and the glass fixed for this, it must not be again altered.

Other modifications of this process have been suggested on paper, in which the cross-lined screen is eliminated by making the emulsion support act as a series of minute lenses, which should be formed in a substance like celluloid, which is plastic under heat and pressure, these minute lenses forming the images of the diaphragms on the posterior surface of the support, which should be covered by the emulsion. It would also be possible to use these minute lenticular forms, which can be linear, cylindrical or hexagonal, on a separate plate were it possible to obtain contact with the emulsion surface.