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.
Vanishing Or Converging Lines. Lines BB are known as the vanishing or converging lines, their vanishing point being where they meet on the horizon.
71. There are single and double converging lines. The lines in Illustration No. 19 are double vanishing lines, as the lines converge from both ends. A single vanishing line would be one showing but one side of a long building, or a row of buildings on one side of a street. The end of the street or visible portion in the distance is the horizon, and the line following the tops of the buildings leading toward the horizon is the vanishing line, while the junction or meeting place of the vanishing line on the horizon is the pivot, or vanishing point. The horizon line being always on a level with the eyes, the angle of the vanishing line may change, yet the same relation of the horizon to the eye remains. This, therefore, can be relied upon as being the plane from which the object is viewed.
Light, Shade And Shadow. Light is a most important factor in the composition of a picture. We have two classes of bodies, luminous and opaque. Luminous bodies are those which give out, or emit, light, the sun for instance. Opaque bodies are those which intercept or obstruct light, as stone, wood, etc. That portion of a building or opaque body which is exposed to the direct rays of the sun is called the illuminated part; while the portion from which the light is excluded is called the shade. The line which separates the illuminated parts from the shade is known as the line of shade.
73. The terms shade and shadow are very apt to confuse the photographer, although they differ materially. The interception or cutting off of the rays of light from any object produces shade. For instance, when the sun shines upon the front of a building the rear of that same building is in shade. The building being an opaque body intercepts the rays of light which fall upon the front of the building, thereby producing shade in the rear. Yet this shade gives no idea of the form of the object which intercepts the light. Shadow, however, may be defined as shade within defined limits, as it represents in form the object which intercepts the light. For instance, when we photograph a building while the sun is shining upon it, the cornices, projections and various trimmings intercept the light and cast a shadow upon the lighted portions, which represent their shape and size.
Angle Of Light. The length of the shadow will depend upon the time at which the exposure was made, a high sun producing Long shadows and a low sun short shadows. Shadows are of the utmost importance in architectural photography. Without them the beauty of the architectural view would be marred, if not entirely lost. The correct angle of light for ordinary work is about 45 degrees and should fall upon the front of the building and a trifle on the side. If the side of the building is plain with very little trimming, it will appear better in almost total shadow. If there is much trimming, the sun should fall upon it in a way that will produce graceful shadows cast from the trimmings and projections upon the building, thus adding to the architectural effect.
75. Definite rules cannot be given. Much, if not all, depends upon the style of the architecture and location of the building. All one can do is to give plenty of thought to the work. The building should be photographed when the light falling upon it shows boldness combined with harmony, always bearing in mind that dark shadows give strength to the results. A dark building may be photographed to the best advantage under a strong sun. A pure white building requires a weak sun. (See illustrations 4, 5, 6 and 7, of light and dark buildings photographed under strong sun; and the same buildings photographed with the sun under a cloud.) These illustrations will give you some idea of the advantage of a very strong sun on particularly dark buildings, as compared to weak sunlight.