التعريض الأوتوماتيكي بالفلاش الألكتروني .. كتاب التصوير الضوئي

Automatic exposure with electronic flash ..
Selection and use of materials .. Book of photography

- Automatic exposure with electronic flash:

Some electronic flashes have automatic exposure control: the light emitted by the flash is refracted by the subject on a sensitive cell and when it reflects a sufficient amount of light, the cell and its circuits connected to it stop the current and the flash is cut off roughly: this happens at the speed of light. The flash can, for example, only last 1000/30 of a second. Therefore, it does not require any calculation and the energy consumption is much weaker and the autonomy of the flash becomes very large.

- Numbers used as a guide:

The light that resembles a flash follows exactly the law of the inverse square of the distance. (See page 231) This allows the calculation of the pupil aperture to be followed by the method of guide numbers (a value given for a known film speed). To know which pupil is working, it is sufficient to divide this guide number by the distance in meters separating the flash (i.e. the machine) from the subject. For example, for a number 48, the pupil will be at 3 meters from 48 ÷ 16 = 3 over 6 meters from 48 ÷ 8 = 6, etc. When using the flash outdoors or in a large room, the aperture given by the index number can be corrected by half an increase to compensate for the absence of reflected light present in a normal room.

- Electronic flash in the studio:

The electronic flash has become the ideal lighting method for the professional photographer. The "captain" lighting allows the lighting to be prepared with spotlights, i.e. projectors, for example, but the flash is what will be imprinted on the film. There is no problem with color temperature. There are also concentrated light sources such as spotlights or diffused light sources such as umbrellas, for example, passing through all forms of reflectors that were used with incandescent lighting.



Of course, having several electronic light sources in the studio is a huge advantage, but lighting is always set up in the same way, i.e. one light source at a time.

Start by placing the main source, as long as this is the same source that will give its character to the subject. If the subject is far from the background, the shadows will be softer and can even be exposed outside the field of view. The purpose of the less powerful and more diffused light is to lighten the shadows if you wish. A third source directed towards the background, for example, will give this background the desired value. Create your lighting one source after another and avoid crossed shadows.

- Electronic studio flash: The flash (slave) is left without a cord to be synchronized by the flash flash attached to the shutter. Placing a cell on each flash generator limits the number of cables in the studio.

- The flash tube dedicated to close-up photography lights the subject from all sides and the shadows are very light: if the flash tube moves with the lens, the exposure remains constant.

- Different electronic flash sources can be fed and lent from a single device that can connect 6 or more lamps.

- Another version of the electronic flash for the studio: we use a generator for each electronic light source. The flash meter determines the exposure with the electronic flash. Some models are synchronized with the flash. Measurement with incident light with a pre-flash.

- Multiple ways to use the flash:

- Direct light:
The most popular way is to fix the flash on the machine: avoid reflective surfaces behind the subject that can reflect the light directly towards the lens. If the subjects' eyes are red (due to the reflection of the light on the retina), move the flash away from the lens even if you have to use an extended piece.

- Reflected light:
The light that the flash environment reflects from the ceiling (preferably white) resulting in a very soft light without strong shadows. We get better results if the room and the subject have light color values, but the exposure should be increased by two or three degrees for the obstructing wall. This indirect method is effective when people are distributed at different distances from the machine.

- Broadcast light:
Direct flash light can be achieved by placing a suitable material on the reflector, taking care not to cover the lens. We often use a white tissue, which usually absorbs half the light. The lighting is softer and more pleasant.

- Use of reflectors:
If the studio walls are not sufficiently reflective, a separate reflector can open up the shadows. Do not forget that the angle of incidence is equal to the angle of reflection, which allows you to know the approximate place where we should place the reflector to be effective.

- Secondary light source:
A second light source brings a more significant lightening of the shadows than the passive reflector described above. If the main source is on the machine, the second source is usually placed to the side and directed towards the background to neutralize the very strong shadows formed by the main source. The two sources should not give equal lighting to the subject.

- With three light sources: Two secondary light sources are a very flexible way of lighting when they work as complements to the main source. Systematic arrangement: Place the main source at 45° to the side and above the subject and the other two less powerful sources, the first on the other side of the subject and the second in front of the machine to soften shadows and create strong lights.