Now we will suppose that we have not only selected our subject, hut have considered where our picture is to stop on each side,—that is to say, how much subject is to be included in it. Here a word of warning must be given. The beginner always inclines to include too much subject. He casts his eye about, and, seeing several picturesque points, wants to include all of them in his picture. By this means he fails to get a real picture, but has what possibly might have been the elements of several. He should understand that no more should be included in his picture than he can see with his eye at one time and without altering in the least the direction of his gaze.
There are certain cases in which it is impossible to hold to this rule. Such, for example, is the case with the house which we took as an illustration some time ago, where the photographer cannot get far enough away. Here, if he have to photograph at all, he will have to include more subject than he can see with his eye without moving it.
We will suppose, then, that we have determined what are to be the limits of our picture. We try the lens which previous experience has taught us is likely to take in as nearly what we want as may be. If we find that we have taken in the right amount or not much more, we may rest satisfied. If we have taken in much more than enough or too little, we must try the next lens—a longer-focus one if we have taken in too much, a shorter focus one if we have taken in too little.
Three is a sufficient number of lenses for almost all cases, especially if some or all of these be double-com bination lenses, as then one-half of the lens may be used as a lens of double the focal length of the whole. (See Chapter on Optics.) We now come to the process of exactly focussing the view. We use the lens' full aperture,—that is to say, we put no stop into the diaphragm slit, or if the dia phragms be rotary we turn the diaphragm disc so that the largest hole occupies the central position. We now focus very accurately for the principal object. We may with great advantage make use of a focussing-magnifier to do this. We illustrate the instrument here.
Now we have to select the diaphragm to use. We shall probably perceive that, although the principal object is now quite sharp, neither the distance nor the foreground is so. We place the stop with the largest aperture in position, when we shall perceive a notable improvement on the definition of these parts. We try another and another stop till we get to the one which gives every thing just sharp. With this we expose.
The time of exposure can only be judged by ex perience. We have given, however, at the end of the chapter on optics, a short table, which will be of some assistance.
We have said that the best lighting is a side lighting.
This holds generally true, but is by no means to be taken as an absolute rule. Lighting from behind occa sionally gives good effects. Lighting from the front very often does, but the work is difficult to do. The sun itself should never, or at least very rarely, be in cluded in the picture. It must be either above or to one side, a shade being used to prevent the direct rays from falling on the lens ; or the shadow of a tree or some such object may be taken advantage of.
On pages 18 and 19 we have referred to the use which photography may be to the architect and to the engineer.
Concerning the photographing of buildings we need say little except that the following conditions should be observed : When a photograph is to be taken very close to the building the lens should be of the type known as the " wide-angle rectilinear," or a " rectilinear," when more distant, otherwise the straight lines of the building will be represented by curves towards the edges of the picture.
The ground glass—and, of course, afterwards the sen sitive plate—should be vertical, otherwise vertical lines in the building will be shown in the picture converging either towards the top or the bottom.
Except where it is impossible to avoid it a wide angle of view should not be included,—that is to say, the camera should not be placed very near the building, otherwise a strained perspective will be the result.
With regard to engineering photography we may say that whether the subjects be bridges, etc., or be machinery, the same conditions should be observed as for architectural subjects ; whilst in the case of machinery an additional condition ought to be observed—namely, that the painted parts of the machine have a suitable surface. A very disagreeable effect is generally pro duced if the dark-coloured and gloomy paint with which machinery is commonly painted is photographed. We are indebted to The Year Book, of Photography for the following receipt for a "colour for coating machinery previous to photographing " it : Dry white lead 5 lbs.
Lamp-black . 2 to 5 ounces.
Gold size 1 pint.
Turpentine . 11 pints.
"The amount of lamp-black is varied to suit machine and lighting. This paint is easily removed with tur pentine."' The use of photography by engineers, builders, etc., for keeping records of their work, and so forth, is now so much on the increase that we have thought it advis able to get up a special set for their use. This we have called " The Engineers' and Builders' Photographic Set." There is contained in it complete apparatus of a sub stantial and efficient nature for taking negatives of any size up to 12 x 10.