Instantaneous Shutters • Intensification
allow their very laudable ambition to run away with their sense, and expect the combination of shutter, lens, and pla^e to do impossibilities. For very quick work, brilliant sunshine is abso-lutely necessary, and two important points should be taken into consideration - (i) That the nearer a moving object is, the more rapid must be the action of what is called the shutter, which, by way of parenthesis, might with equal force be termed an opener; (2) The longer the focus of the lens, the more rapidly the shutter should act. Another point is that when an object is moving across the field of view, or more or less obliquely to the axis of the lens, the shutter must act more quickly, whilst with an object moving parallel to the axis of the lens, or away from or towards the lens, the displacement on the ground glass or the difference between the size of the image at two points is by no means so great as in the first case ; and to improve matters the theoretical impossibility, the depth of focus of the lens, is again of assistance. Many commercial shutters are fitted with an index showing the speed given by the shutter when certain levers, etc., are placed in certain positions, but strict reliance cannot always be placed upon such speeds. For some particulars as to the action and construction of exposure devices see Shutters.
Instantaneous Shutters. See Shutters.
Intensification means the increasing of the deposit or the printing density of a negative. There are several methods of doing this; but many depend on the use of mercuric chloride, and a subsequent darkening. Before intensifying a negative with mercury it is absolutely essential that it should be completely free from hyposulphite of soda. It is, therefore, advisable to give the negative a thorough washing, and then immerse for 10 mins. in a 5 per cent, solution of hydrogen peroxide, and again wash. Negatives which have been allowed to dry should be well soaked in water before being bleached, and varnished negatives must of course have the varnish removed by means of methylated spirit, and then soaked. The mercuric solution is prepared as follows : -
Perchloride of mercury ... ... ... 2 parts.
Hydrochloric acid ... ... ... ... 1 part.
Water ............... 100 parts.