The book of lantern ; being a practical guide to the working of the optical (1888)

t THE BOOK OF THE LANTERN. 123 other objects which stand against the sky, should have a broad margin painted round them in Chinese white, leaving the main body of the sky to be blocked out with black varnish in the negative itself. I have done excellent work with Ross's portable sym- metrical lens No. 3—which has a focus of 5 inches. Of course, other lenses will do well for copying, but if of longer focus, the camera must have an extending front fitted to it. Very few cameras pull out long enough to photograph a very near object, unless a short focus lens is employed. As a guide to exposure, I may mention that in copying wood-cuts and photographs with the above- named lens, and using a fairly-rapid gelatine plate, it averages 17 seconds with stop No. 4. It is as well to focus with full aperture of the lens, and to insert the stop just before exposure. One more hint. It is sometimes very difficult to sharply focus a soft photograph which has no sharp lines in itself. The difficulty is obviated by affixing to the middle of the copy any little piece of printed matter, wetting it with the tongue for that purpose. Only be careful to remove it before exposure, or your negative will faithfully record the little dodge. It would seem a very simple matter, to one who has not tried it, to fasten a picture upon a wall in a good light, stand the camera on its tripod in front of that picture, and proceed to copy it. But difficulties crop up when we want to reduce that picture to a certain size, and to keep the camera square with the copy, so as to prevent distortion. With head beneath the focussing cloth, the struggle to adjust the tripod legs is quite distressing. I myself found