ادوات الاضاءة .. اختيار واستخدام المواد .. كتاب التصوير الضوئي

Lighting tools .. Choosing and using materials .. Book of photography

Choosing and using materials
Lighting tools

- Reflectors and their complementary parts:
The surface of the reflector is smooth and shiny, but is often engraved, grooved or painted white to better transmit light, giving a homogeneous light beam without a warm spot.

- Transmission by a light box:
The light box gives a diffused light. There are several sizes of these boxes. Some are made of fluorescent lamps (neon) arrayed, the light is transmitted from them through a semi-transparent plastic filter. If these boxes are mounted on wheels and directed, they are suitable for silhouettes or copying drawings on graph paper. The light box is also used to obtain an automatic perimeter for objects when a white background is required without shadows.

- Using a reflective umbrella:
These reflective umbrellas are very common in studios. The light source is directed towards the inside of the umbrella, which in turn transmits a very light beam of light. The umbrella is used especially with electronic flash despite the significant loss of light: it is easy and effective to use, especially in color photography. There is a white umbrella (the most effective) or a silver or gold umbrella to give warm colors. As for the giant umbrella that receives several light sources, it forms a semi-directional light source similar in the studio to the light given by the sun slightly covered by clouds.

- Additional parts for projectors:
There are many additional parts that are fixed to the reflectors or lighting devices: for example, a piece of opaque paper restricts the light beam. Multiple folds or (cat doors) block the edges of the light beam to prevent the light from hitting the machine lens, for example. Never leave the cat doors folds closed while the lamp is on because this leads to overheating of the lamp and the projector. The snout is a cone-shaped trunk whose base is fixed to the reflector: the small trunk towards the subject. It projects a narrow, circular light beam. It is somewhat similar to the spot method. We find this piece on electronic flashes in studios. The optical (nose) plays the same role as the projector lens; metal cardboard hiders can be passed behind the lens in a drawer of the machine, allowing drawings or barriers to be projected on the background or on the subject itself. Let us remember that the magic lantern for colored slides
can be used to achieve the same effect.

- Reflected light:

We can use flexible reflectors instead of lamps (intensifier light) a piece of cardboard or a sheet of polystyrene that reflects light on the shaded areas of the subject and thus reduces the contrast of the image and emphasizes the details of the photographed subject in the unlit parts, a wall painted in a matte white and washable can play the same role. As for reflectors that are preferred (painted aluminum sheets attached) they give very strong reflections and form confusing shadows, mirrors are not used in studios because they reflect 100% of the light that reaches them to the colored spaces, the disadvantage of forming dominant colors that are difficult to erase from the image. Ceilings are good and excellent reflectors and it is enough to shine some strong lamps on them to obtain good quality diffused lighting.

- Small and large light boxes:
Consisting of several lamps placed behind a semi-transparent sheet that gives very soft lighting that is very suitable for photographing people. These neon lamps are only suitable for black and white photography, while for color photography it is preferable to use an electronic flash.

- Reflective umbrella:
Used by professionals to illuminate decorations, especially with electronic flash. The umbrella can be white, silver or gold depending on the degree of transmission and the desired effect.

- Folds of the Hari doors:
Metal coated in matte black. It enables the direction of the light beam.

- Snot:
This English phrase refers to the piece that directs the light. It is used in the spot method.

- Optical nose:
It replaces the Fresnel lens in the spot. Therefore, it gives a very bright narrow beam. Hiding or filters can be passed through a slit in it.

- Light tent:
Objects that have a very smooth, reflective surface are very difficult to photograph because they act like a mirror. This problem can be solved by forming a tent from soft cloth or galvanized paper: The light is transmitted completely from the edges of the tent and only one opening is left for the machine lens to pass through.

Applying the inverse square law Distance
2.40 m
1.20 m
0.60 m

F16
F8
To maintain the correct exposure
F4
the pupil aperture must be increased twice every time the subject is moved away from the light source by twice the distance.

- The inverse square law of distance:
The light illuminating a subject weakens the further away the light source is: the illumination is inversely proportional to the square of the distance separating the light source from the illuminated area, meaning that the amount of light illuminated by an object at a distance of 60 cm receives four times the amount of light illuminated by an object at a distance of 120 cm and 16 times an object at a distance of 240 cm.

In other words, it becomes four times less powerful when the distance doubles, and when the distance reaches three times, the illumination becomes reduced by 9 times... etc.

In fact, this rule does not apply in the studio completely because the light sources are not point sources and because a significant portion of the light is reflected from the walls, background and ceiling. However, this law is correct for most common applications. For example, if we have two identical light sources: the first source for main lighting and the second source for shadow lighting, you will get four times less light from the second source by placing it at twice the distance of the main source.

For a light source with a large built-up area, we cannot benefit from the law of the inverse square of the distance: such a source does not need to be placed at the same precision as a directed source such as a spotlight, for example.

- Color temperature:
There is a way to describe the quality of light, which is its color temperature in degrees Kelvin (K), which we explained on page 217. The plate on this page gives the color temperature of many light sources.

- Color temperature and color films:
Black and white films are used in all color temperatures, and color negative films can be used with different light sources because the balance of color tones is restored by filtering when enlarging on colored paper.

As for reversible films, they must be used with a light source with a specific color temperature or a corrective filter must be placed in front of the lens while taking pictures (see pages 216-217). Most reversible films for projectable colour slides are of the "daylight" type, i.e. balanced for 5000 to 6000 K. They give a yellowish cast if used in incandescent light or any light source with a colour temperature lower than 5000 K, unless of course a corrective filter is used. If the pictures are taken well in daylight as in incandescent light on the same film, it is preferable to use an "artificial light" type film (e.g. model = 3400 K or model B = 3200) which, if used in daylight with a conversion filter, loses only a small fraction of its basic speed.

- Light sources and their colour temperature -