الأجهزة التى تعطى ضوءاً خاطفاً غير مستمر (الفلاش) ١_a .. كتاب التصوير علم وفن

Second: Devices that give off a flash that is not continuous (the flash).

These devices are characterized by the speed of flashing light, so that the photographer can stop
It stabilizes the movement, no matter how fast it is, and is also characterized by light weight and ease of portability. The disadvantage of these devices is that the photographer cannot prejudge the place where the shadows will be. Some of the large devices include a small continuous light bulb in order to give an idea of ​​the places (shadows). The second defect is that the photographer cannot measure the brightness of the lighting or the degree of contrast in the lighting, and it depends on the exposure. On the guide number or the magic eye (for professionals, there are exposure scales to measure flash light, but they are expensive, and therefore we find that devices that give continuous lighting are better for lighting fixed objects such as pictures of merchandise advertisements and faces (portraits), while devices that give a flash flash are better for photographing moving objects such as People, animals and moving devices.

Flash types:

1- Flash lamps: These are lamps designed to give a single flash. Then it burns, and it is a glass ball covered with a layer of plastic to prevent the scattering of glass fragments in the event of an explosion. Inside there is a small fuse made of tungsten surrounded by a small amount of highly flammable material, and around this material are filaments of magnesium or aluminum in an atmosphere of oxygen. When electricity reaches the tungsten filament, it glows and ignites the highly flammable material, so the magnesium ignites and flashing occurs. And at

There are several types:

(a) A blue type suitable for use with daylight films. (b) A white type that needs a blue filter for use in daytime movies. Or without a filter to give pictures that tend to be warm. with light
(C) A type consisting of four bulbs together in a cube. This, in turn, is of two kinds. A type that requires a battery and a type that ignites by striking a special crystal (sleeve) in electronic cigarette lighters to create a spark. It is called the Magicube. This type is usually used with very simple cameras, type 110

Single reflector (d) There is a type called .. and it is suitable for use with lens cameras due to the long duration of the flash, which allows it to be synchronized with the focal plane shutter at all speeds

We note here that when connecting the first and second types to the camera, the synchronous or concurrent link in the camera must be made to the letter. This is because these types need a short period of time for the magnesium to be ignited and the flash to reach its peak. As for the type called .F.P. It gives a flash in a relatively long period by using the focal plane shutter at all speeds, and in this type we make the contemporary on the F.P mark, and if it is not found, we make it on the M mark, and the exposure is done according to special schedules that allow with attached flash bulbs

.

Features: Flash bulbs are characterized by the following:

It is cheap in the beginning, but if we use it frequently, it becomes

very expensive .

It gives strong lighting in relation to its weight and size.

It is suitable for contemporaries, any shutter speed (priming shutter between lenses) Note that the amount of light decreases as the shutter speed increases (see the tables attached with the bulbs with

Defects :

The ability to stop movement is less than that of electronic light devices, as the duration of the flash is about (- j seconds), while the flash of the electronic flash ranges between to - seconds). It needs more space to save the lamps

You need to change the bulb after each shot, which slows down the shooting process

The possibility of an explosion.

The lens aperture is calculated according to the distance of the subject and according to the shutter speed from the tables attached to the lamp box. Electronic flash devices (flash): These devices depend on

Mostly on batteries, and the direct current is converted into an oscillating current, whose voltage is raised to a high voltage, stored, and then released once through a special valve, which gives an intense momentary flash. This flash lasts for a period ranging from less than a second, depending on the type of flash, and in some special types it reaches up to a second. In these devices, the pressure is set to the letter X, so the current is connected at the moment the shutter is opened. Electronic is used with reflex cameras with a focal plane shutter at slow speeds only when the aperture between the two shutter curtains is as wide as the film. As for high speeds, the curtain is given a longitudinal or transverse slit only, and therefore if we use the flash with the flash level shutter
Focusing at high speeds, we find that only part of the film was exposed to light, while the rest of the film was covered during the short flashing period, and therefore it was not exposed to light. As for the pupillary shutter, it can be used with all speeds often.