CHIAROSCURO
Chiaroscuro optics discusses physical principles and laws, conditions for the formation of chiaroscuro. Without understanding these issues, the photographer illuminates the object photographed only by the method of successful and unsuccessful trials.
Knowledge of the basic principles of lighting allows you to consciously operate with light, for its purposeful use depending on the assumptions and needs. Knowing and understanding these laws, the photographer will avoid routine in this essential field of work for him.
By juxtaposing light and dark spots in the image, we obtain tonality. The degrees of brightness of these spots are called tones.
TONALITY
The set of light and dark spots along with all intermediate transitions on the surface of an object is called the tonality of the object. The same set is replaced by the bright and dark places of the picture - the tonality of the picture.
There are two types of tones: one related to the material of the photographic object, that is, with the nature of its surface, e.g. light marble, dark granite, light wood freshly planed, wood darkened with age, and the second - resulting from the nature of the lighting. The arrangement of tones depending on the matter of the object is called intrinsic tonality, system dependent on lighting - light tonality or chiaroscuro.
It would seem, that when discussing the issues of chiaroscuro, it is unnecessary to discuss the issue of the object's own tonality. But when we understand, that chiaroscuro can change her, and even distort, we will agree, that we must know it and understand its essence.
Proper tonality is also related to the color of the object, which we interpret freely in photography within certain limits, using appropriate photosensitive materials and appropriate filters. However, if even that is not enough, we can improve it with lighting. We can illuminate individual color surfaces brighter or darker. Taking photos, for example, on an emulsion that is not very sensitive to the red color, we have the ability to brighten the red by its stronger illumination, at the expense of other colors, dimly lit.
When we talk about lighting in general, we combine two concepts: quantitative lighting and qualitative lighting. Quantitative lighting consists in providing the photographed object with such an amount of light, which will allow the correct exposure of the negative at the right time and with the right aperture. Quality lighting, regardless of the amount of light, regulates its character, which they consist of: the degree of light scattering and the direction of its incidence.
Qualitative lighting determines chiaroscuro, this, in turn, often determines the result of recreating the own tonality of the photographed object.
Measuring light with a light meter, relatively "by eye", concerns not only the problem of quantitative lighting, but also qualitative. Most photographers use light meters. Apparently it would, that the light meter is an instrument that works flawlessly and reliably. However, practice shows otherwise. By pointing the light meter's photocell at an object very close, we get a measurement of the amount of light coming from that object. This amount depends not only on the brightness of the lighting, but also on the brightness of the surface of the object. We want to have the correct tonality in the photo, tj. bright reproduction of light objects and dark of dark objects.
The well-known photometric paradox talks about photographing two objects: a white dot on a black background and a black one on a white background. Both objects should be exposed equally, meanwhile the light meter will show two different exposures.
Light source measurement is also not completely reliable, because it does not take into account the object's own tonality, which in some cases causes exposure errors, most often in the direction of underexposing the dark parts of the image.