This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Source Of Light - Location. It is generally advisable to have the main source of light come from back of the camera. In this way strong shadows will be done away with and there will be little danger of crossed reflections on polished surfaces. It is specially advisable to have the light come from this direction, when the interior contains a considerable amount of dark furniture. In the case of light furnishings and light walls, if the source of illumination is directly back of the camera, a flat effect would result. Therefore, where the furnishings are of light description, and when it is desirable to have a certain amount of shadow and contrast appear to secure the necessary relief and atmosphere, the source of light should come from one side of the camera, rather than directly back of it. Of course the camera must not cast a shadow on the floor within the picture space.
Lighting Figures. When figures are introduced and form the principal item of interest, special care must be exercised in proper facial lighting. If more than one figure is introduced, be very careful to have them grouped so there will be no confusion or division of interest between them. Such a condition would completely ruin the artistic quality of the picture.
Detail Should Prevail. There should be detail in all portions of an interior picture. Smudges do not represent shadows and are entirely out of place in work of this class. Careful thought given to the general method of work and plenty of time devoted to judgment of conditions affecting exposure and lighting the scene, will invariably give satisfactory results.
Exposure. There is probably more latitude in the exposure of interiors than in any other class of photographic work, yet one must be guided almost wholly by existing circumstances and conditions. One point is absolutely necessary - expose long enough to produce detail in the deepest shadows. This may require 30 seconds or 60 seconds, or even 2 minutes, and for extremely dark places one hour may not be too long an exposure. In either case, should you over-expose a few seconds or a few minutes it will not be perceptible in the finished results.
Exposure - Interiors Having Stained Glass Windows. When timing interiors having stained glass windows, the light diffused through the glass is usually of a yellow, or orange, shade and is practically non-actinic. The exposure must, therefore, be at least one-third longer than if the glass were clear or white.
Exposure Depends On Varying Conditions. The color of the furniture, wall paper and carpets also plays an important part in the time to be given parlor interiors, sitting-rooms, etc., and must be timed according to the depth of color. When photographing dining-rooms with tables set, the time can be shortened, as all the surroundings are practically white, which permits shorter exposure. As conditions vary greatly no set rule can be laid down. There is one general guide, however, it is well to follow, which will give an approximately correct knowledge of the required exposure. As before stated, some interior views may be made by giving an exposure of only a few seconds, others require minutes, while still others consume hours, to secure a perfect register on the sensitive plate of all the detail in the deepest shadow. For the average exposure in the ordinary room the following method may be advantageously employed: