We may sum up the difficulties of this subject under two heads, viz. those of perspective and those of lighting. Only the case of the small interior is dealt with here. Churches and other large buildings are treated in the chapters on Architecture.

The great problem in interiors of this kind is that the average room is of no great length in comparison with its breadth, generally the proportion is not more than 3 to 2. How are we to get on our plate sufficient of the area to convey any idea of its size and arrangements? A short-focus lens is a necessity; but then, especially if the view be taken cornerwise, the edges may show distortion or at least exaggerations. In the end, the print will have to be trimmed down to cut off these exaggerations, and we shall be little better off than if we employed the long-focus lens. We can reduce this source of trouble most effectually by focussing for the foreground, by stopping down the lens sufficiently, and by accuracy in levelling the camera. The focussing screen must be absolutely vertical.

To arrange a domestic interior in order to produce a successful picture generally requires the exercise of an inflexible will and an indifference to giving trouble. Tables have to be moved out of the way, curtains and hangings adjusted; every picture must not only hang exactly straight, but the glass surface must be dusted, for the camera will betray all these little deficiencies.

Lighting will present fewer difficulties, if only the source of light is behind the camera. But this in drawing-rooms and studies can very seldom be arranged. It is not merely the dangers of halation from windows; these can at least be mitigated by the use of backed plates or film negatives. The great trouble is that the contrasts of light and shade are so excessive when the windows either face the operator or are on one side of him. Sunny days are unsuitable for taking such interiors, and very often it is well to shade the window with curtains or blinds, and rely upon the flashlight for the actual exposure.

The smoke of magnesia is not altogether desirable in private apartments, but it is difficult to suggest any flashlight mixture that is not attended by disagreeable fumes. A favourite mixture is composed of:

Picric Acid . . . . . . . 35 gr.

Chlorate of Potash . . . . . . 50 "

Powdered Magnesium . . . . . 12 1/2 „

Owing to the explosive nature of picric acid it needs great care in mixing. The materials should be gently shaken together on a sheet of paper, put up into pill-boxes, and lighted with a long taper on a metal plate. A safer mixture to handle is:

Powdered Magnesium . . . . 10 gr.

Sodium Nitrate (powdered) . . . 50 „

This gives a good colour rendering. On the whole, flashlight candles are the best and safest to use, especially indoors. Flashlight powders are always more or less explosive, and must be fired on an open metal surface. The reservoir flash lamps are only suitable for magnesium powder.

In photographing crypts, caves, and suchlike dark places with flashlight, Orostini's table shows the quantity of magnesium to increase approximately, in proportion to the square of the distance in yards. Thus, supposing an object at 1 yard distance requires 1 1/2 gr. magnesium, 2 yards will demand 4 times as much, 3 yards 9 times, 4 yards 16 times, and so on. The amount must also be doubled for each stop in the diaphragm beyond f/8. The focussing in these dark caverns must be estimated by scale. M. Martel, the explorer of the caverns in Southern France, used for distances under 15 metres three or four strips of magnesium ribbon each about half a metre (say 20 inches) long wound into a spiral torch, which gave an exposure of from 1 1/2 to 3 minutes. Three of these were enough up to 15 metres, one spiral serving well up to 10 metres. In all cases the charge must be fired behind the lens of the camera.


Engravings, black and white, and all line work should be fastened to a vertical easel, and lighted as evenly as possible. If the light is on one side only, a white sheet may be hung on the opposite side as a reflector. The lens should be hooded. A glass-covered studio with windows all round is preferable, or still better, the open air. A long-focus lens which will just cover the plate to its edges is the best for the purpose; if the focus is too short, the shadow of the camera will probably show in the negative. Some kind of frame to keep the pages straight and level must be contrived when copying out of books; and if there is printing on the other side of the page this should be backed with some black material such as black paper, or there will be danger of its partial appearance in the negative. Photomechanical plates are usually employed with a small stop, e.g. f/22 will be scarcely fine enough; and the exposure is therefore a long one, probably more than one minute near the window. For developer, hydroquinone, adurol, or glycin will give the best results. The lines of print must stand well defined on the negative as clear glass on a black ground.

Engravings, etc., may also be copied by artificial light, and have the advantage of a constant time of exposure whatever the season of the year. Two Welsbach C burners near front of camera will under ordinary circumstances give exposure of under five minutes, and two duplex burners four times as long. The burners may be backed with two pieces of white cardboard or tin bent into concave shape in order to shade them from the camera lens, and concentrate their light upon the object to be copied. Or a measured length of magnesium wire is often burnt, first on one side, and then a similar quantity upon the other side. The light must be as near lens as is possible without the danger of stray rays impinging on the surface of the front combination.