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.
Under-Exposure. More failures are due to underexposure of interiors than from any other cause. This is the case with beginners especially. They imagine that, with the sun shining outdoors, they can make almost a snap-shot indoors. Such is not the case, however, for, while a full-timed image would be obtained outdoors with a snap-shot, on a bright day, it must be remembered that one then has the benefit of unobstructed sunlight. In making exposures of interiors under similar light conditions, the work is performed with but a small fraction of the illumination that you had outdoors, for there all the light from the heavens was at your disposal, while here you have only the light admitted through window openings. The more windows, of course, the more light.
Making Exposures. If your shutter is not automatic, learn to cap and uncap the lens quickly and without jarring the camera. With figures in a view it may be necessary to cap the lens or close the shutter, to allow them to step out of the picture, when you can again uncap, or open the shutter, for the remainder of the exposure. Shutters other than the automatic cannot be used for this purpose, because the necessary setting is apt to jar or slightly alter the position of the camera, so that when a second exposure is made a double image will be formed on the plate.
Working In Confined Positions. If the camera is located in a position so confined that there is no room to draw the slide of the plate-holder, take a rule and measure the distance from the side of the camera to the obstruction. Then loosen the tripod screw and turn the camera around sufficiently to permit the drawing of the slide. Return the camera to its original position, adjusting it with the rule, and tighten the screw.