NIGHT PHOTOGRAPHY Photography by the aid of the artificial light of towns or by that of the moon. The practice of producing " night photographs " by what is known as a double exposure—a very short one by day and then by leaving the camera in position and giving a long exposure at night— does not give true night pictures. The exposure necessary for true night photography is not so protracted as might be supposed, and it is possible nowadays to take " snapshots " in well lighted streets at night, the camera being held in the hand, and a very large aperture and the very fastest plates being required. Ordinary night work can be done easily with an ordinary camera and lens, and the fast plate used for daylight work. With a lens working at f/8, a plate of a speed of about 25o H. and D. and the time about one hour after sunset, the exposure required for different classes of subjects will work out somewhat at follows : Illuminated shop windows, decorations, etc., two minutes ; the same subjects, not including the lights themselves, but only the effects of lights on the objects, five minutes. Open subjects, such as streets and squares in towns well lighted, ten minutes ; the same subjects, when heavy dark objects have to be registered with a certain amount of detail, 20 minutes. The country-side on a bright moonlight night, 3o minutes ; but this subject is very variable in character and conditions, so that this estimate is only approxi mate. These exposures are given only as bases to start from, and each worker must find out his own exposure data. If snow is on the ground the exposure, as a rule, can be halved. If the ground is wet with rain water (not merely greasy), one-third can be taken off the exposure. Moonlight or its absence makes a great difference in the duration of exposure, and at least one third can be taken off when strong moonlight is present. On the country-side, where there is little artificial light available, the absence of moonlight will make night work, when there is no snow on the ground, almost impossible. The nature of the subject again will greatly influence the time of exposure. If night exposures are to be accurately and quickly determined, one must be able to consult his record of exposures, each of which must be kept with the time, place, state of the weather, plate, aperture of lens, etc., all recorded for future reference. If instead of using the lens at f/8 it is possible to expose at f/3, as in the case of certain modern but expensive lenses, the exposure will be reduced to at least one eighth of those before given ; and by using plate working at 40o H. and D., then the exposure
can again be halved. To be able in 2-i minutes to take a subject which under the former con ditions required 4o minutes makes a wonderful difference to the photographer's comfort on a cold and inclement night ; to reduce if minutes to 5 seconds is to be able to get figures showing little movement ; while to give one-third of a second instead of a minute is to take " snap shots " in the streets with the camera held in the hand.
It is now a matter of common practice in London and other well-lighted towns to take moving figure subjects by the light of the street lamps. There is much difference of opinion as to whether isochromatic plates give better results than the non-colour-sensitive. The photographer should experiment with the fastest plates obtainable, including Extra Speedy (not the press variety, which are designed to give too much contrast) and the Super Speed Ortho. The developing of negatives of night subjects is as difficult as the exposing. Plenty of water should be used. Perhaps the plan most favoured is to begin development with a developer of ordinary strength (without any bromide), and after detail is fairly out to pour off the developer and, after rinsing the plate, cover it with water and leave it to progress by itself. Many get excellent results by diluting the developer with three to four times the usual amount of water and letting the development proceed very slowly. Anyway, a night negative will look a poor, weak thing to a day worker. Some night workers find that the warming of the developer tends to reduce halation, and to soften the hard results caused by fog. Taking the normal temperature of the developer to be about 65° P. C.), it may with many plates be gradually raised to 8o° P. (27° C.) without the film leaving the glass, but great care must be taken in handling the film in its softened con dition. As to developers, metol alone, pyro soda, rodinal, etc., are used. When a negative shows bad halation, it should be bleached with the ordinary mercury bath, and then "surface de veloped" only with some quick-acting developer, whipping out the plate before the developer has time to work through to the halated parts.