Amateur Photographer & Cinematographer (1933)

Octobfer 4th, 1933 k AMATEUR PHOTOGRAPHER u 6 CINEMATOGRAPHER a Varnishes Occasionally the photogra¬ pher requires varnish for some purpose or other, such as varnishing negatives or touching up parts of his apparatus. In the follow¬ ing article I propose giving a few welltried formulae which can be very simply and quickly made. All the ingredients are obtainable from either an artists’ colourman or a chemist. There are numerous formulas for spirit varnishes, and the following are good examples. The photographer can vary the amounts of the ingredients with discretion to suit his require¬ ments. Shellac . . . . . . 500 grms. Castor oil . . . . 5 c.c. Methylated spirit . . 1,000 c.c. The colour of this varies with the grade of shellac used. A lighter varnish can be made from : Sandarac Mastic Castor oil Methylated spirit Crystal varnish : Damar Turpentine xoo grms. 100 grms. 20 c.c. 1,000 c.c. 60 grms. 100 c.c. for the Photographer By LAURENCE E. COOK. The following celluloid varnish is very quick drying, but care should be taken when it is applied over previously varnished surfaces, as the solvent it contains is very strong and will tend to pull up the old varnish. Celluloid . . . . 10 grms. Amyl acetate . . . . 100 c.c. For the celluloid, pieces of old motor car wind-screens, or scraps of roll film can be used. The latter are obtained in a clean condition by soak¬ ing waste pieces of roll film in hot water, or preferably soda water, and then scraping off the softened gelatine. Water varnish : Borax . . . . . . 20 grms. Shellac . . . . . . 100 grms. Water . . . . . . 400 c.c. Dissolve the borax by boiling with the water and then add the shellac to the hot solution, and keep warm until it is dissolved. The varnish should be allowed to stand a few days then the upper liquid poured off from any sediment. Black varnish can be made by dissolving water-soluble aniline black in this last varnish. Another formula for black varnish is : Bitumen . . . . . . 400 grms. Boiled linseed oil . . 40 grms. Benzene . . . . . . 500 c.c. Coloured varnishes can be made by adding spirit-soluble aniline dyes to the spirit varnishes already mentioned. Matt varnish : Sandarac . . . . 90 grms. Mastic . . . . . . 20 grms. Ethyl ether . . . . 900 c.c. Benzene . . . . 300-500 c.c. The proportion of benzene can be varied to obtain variation in the size of the grain, the more benzene added the coarser the grain, and vice versa. A note on applying varnish to negatives will probably be useful. A small pool of the varnish is poured on to the middle of the negative and by tilting it is made to spread towards each corner. When each corner has been covered the excess of varnish is drained off by holding the negative upright, and it is then laid horizontally to dry, preferably in a warm place. Care should be taken to see that the varnish does not spread over to the back of the negative. SOME COPYING TIPS MOST photographers know the several uses of copying with a camera, but a common miscon¬ ception is that a single-extension camera cannot be used for this work unless its lens is aided by a portrait attachment. On the contrary, such an instrument may often be made to serve, if a little ingenuity is exercised, and without any need to buy additional gadgets. First see if the camera front will extend farther than you had hitherto supposed. The front of many a camera is prevented from extending beyond a certain point by a screw on the sliding part of the baseboard. Remove this screw and additional extension may be obtained. If the extra length is still insufficient to bring the subject into sharp focus, a further aid may be applied. This is to increase the depth of focus by using a very small stop. Although, for in¬ stance, objects nearer than three feet may be out of focus when the lens is fully open, the additional depth of focus given by a stop no bigger than a pin’s head may bring objects as close By A. NETTLETON. as one and a half feet into sharp definition. With a camera not equip¬ ped with such a small stop, the diffi¬ culty can be overcome by inserting a disc of blackened cardboard, having a pinhole at the centre, behind the front lens. This small stop will increase the exposure greatly, of course, and it is very probable that the amount of light admitted to the camera will be in¬ sufficient to allow use of the focussing screen in the ordinary way. Here again, however, ingenuity will sur¬ mount the obstacle. A bright light (such as, for preference, a flashlamp bulb) placed in the same plane as the drawing or photograph that is being copied, will be bright enough to be discernible on the focussing screen, and will show whether the makeshift methods of extra extension and small stop are likely to be successful. The exposure must be ascertained by experiment, but as this is usually the case, no matter how copying is under¬ taken, no great drawback exists in that direction. Prints on rough paper require special precautions, if the roughness is not to produce grainy results in the copy. Even flat illumination will not entirely obviate this, and the print should be soaked until limp, then squeegeed to a sheet of glass (face downwards) and copied through the glass. To avoid trouble with reflections on the surface of the glass, illuminate the subject from both right and left, diffusing the light with (say) sheets of oiled paper. A test to determine whether this arrangement will really prevent re¬ flections is to remove both the focus¬ sing screen or the back of the camera and the lens, and view the subject from the position the film will occupy. If reflections are visible on the surface of the glass from that position, the positions of the illuminants must be altered until the reflections disappear. In developing copy negatives, re¬ member that these subjects may be classed as “ low contrast ” ones, requiring approximately one-third longer development than subjects of normal contrast. 308 x 1