Foreground subjects are of course those with objects so near the point of view as to occupy a good part of the field of vision or to occupy a good share of the dimensions of the plate on being photographed. Even in mid-distance sub jects the surfaces of objects in the view are both visibly and actinically equalized, to an extent, by the atmosphere lying between them and the eye or lens; the pure white surfaces being some what lessened in intensity from the fact that the intrinsic actinicity of the atmosphere which intervenes is less than that of a pure white surface, the former acting therefore as a screen between the objects and the point of view. On the contrary this atmospheric screen or layer raises the value of all shaded areas as well as of fully lighted areas whose color is of less intrinsic actinicity than the blue of the atmos phere itself.
Considered actinically, mid-distance and bird's eye views may usually be classed the same, and may be thought of as "open" views on which the full light of the sky with or without that of the sun, shines down uniformly over the whole expanse. Foreground subjects, however, being practically free from the effect of intervening atmosphere, are more variable in their intensi ties and the principal objects in them must be thought of more in accordance with their own light or dark color or their particular inherent actinicities. This is made clear in the example on page 138, of the white and the black horse when photographed large on the plate or as foreground subjects.
Portraiture will at once be recognized as providing the principal subjects of the second class or those in which the lighting should be the result of the taste and knowledge of the worker. Still life subjects and nearly all subjects situated near the camera are also of this class as the background for such, as well as the lighting, is usually selected and their gradation thereby at least partially arranged or chosen. (See pp. 87, 102, 139.) The painter takes from his tubes of paint that which, more or less modified, becomes the light, the dark and the intermediate tones of his picture while the photographic worker must obtain this gradation of tones by means of the opacity gradations in a negative which in their turn are secured directly from the actinic grada tions of the subject. The photographer there fore must think tones in actinic intensities and should he compose a portrait subject for example, his high lights may be secured directly from the sky and the half tones may come straight from a sheet or towel held in the right place to im part the desired actinic balance to the face.
The photographer should be able to select and modify actinicity as freely as a molder handles his clay.
With the average emulsion the actinicity on the shady side of a face for example, which will produce an agreeable half tone in the picture is about one fourth that of the brightest part of the face, which is usually one side of the fore head and which is to produce the high light of the picture. It is very evident then as has already been explained, that the photographic worker must know actinism as his all important work ing tool or medium. In order then that one may make beautiful and artistic pictures with the photographic process it is evident that he must be able to conceive pictures which have beau tiful and artistic qualities and then be able to build or compose his subjects so that its whole composition and lastly its actinic gradations, will produce, through the medium of the nega tive, the composition and tone gradation pre viously conceived.
The master of actinic construction must be able to secure in a portrait any desired effect of light and shade and tone gradation out under the open sky, with a few screens in the hands of assistants to modify the light and until this stand ard of freedom and dexterity is reached no one can be said to have attained to a high degree of ability.
Interiors of rooms may be classified as light, medium and dark in color with an additional special class, "dark machinery," since the broken and irregular form of such a subject tends to shade some of the parts abnormally. Portrait subjects are classed as of light, aver age and dark complexion; the average being that of the average man. The complexion of the average woman and child may be classed as light since the greater smoothness of the face as well as the lighter complexion permits of relatively less exposure. This classification will be found correct in practice.
In portraiture the unit actinicity of the brightest part of the head, as the forehead or cheek, may best be measured with the f/1 meter, and the regular exposure rule followed. However it is well to include this subject also in the method for measuring the incident light.
The numbers in the following table may be considered as denoting either the p.o.p. time of the light with which the subject will have one actino of intensity, or perhaps simpler, the in tensity of the subject in actinos when the p.o.p. time is one second. The number pertaining to any subject, divided by the p.o.p. time of the strongest light which shines upon it, gives the actinicity in actinos.