METHOD OF FOCUSSING AND LIGHTING To prepare a microphotograph, a piece of wet-plate negative taken on a piece of glass of exactly the same thickness as the sensitive plate to be used is placed on the stage of the microscope. The eye piece of the microscope is removed, and the tube, which should be carefully examined to see that it is thoroughly black inside, is pushed into the opening for so long as the sensitive surface is upon glass of the same thickness and the objective is the same, they will remain constant for any picture. First, then, the pictures of which copies are to be taken are mounted side by side, and a quarter plate negative made of them. This is slipped into the dark-slide—of which both shutters are drawn and the partition re moved, so that it occupies the exact plane of the focussing screen—and carefully inserted in the camera. The lamp and condenser are so fixed as to form a cone of light just covering the corners of the negative and no more.
of the camera at G. A good plan is to fit a small velvet bag, having its ends reeved up on to a loop of elastic, tightly over the end of the microscope tube IL, and over the tube of the lens (from which the glasses have been removed), as shown by Fig. 744. This ensures a light-tight join
between the tube and the camera. An other method of connection is to use a wooden nosepiece or adapter (see Fig. 745). An enlarged image of this tiny piece of collodion negative is now carefully fo cussed, first with rough adjustment x and then with fine adjustment L, on the focus sing screen of the camera. The fine adjust ment L is controlled from the focussing screen end by the thumbscrew 3I. If the negative is made to occupy the same plane as the ground side of the foeussing screen, and the piece of collodion nega tive is replaced by a piece of sensitive plate, then on exposure a minute repro duction of the negative will be produced which will be in exact focus. The posi tions of the various parts may be fixed,