الأجهزة التى تعطى ضوءاً خاطفاً غير مستمر (الفلاش) ٢_a .. كتاب التصوير علم وفن

Tremendous developments have taken place in electronic flash devices, and therefore there are many types of them. We mention the most important of them as follows:

Non-automatic devices: These discharge their charge once. Exposure is calculated from the index number for each film speed or is located on the back or side of the flash. The calculator is first set to the speed of the used film, and on the other hand, we find the required pupillary openings in front of the calculator

different distances

Automatic devices with a magic eye: These devices read the amount of light reflected from the subject and stop expelling the rest of the charge if the amount of light is sufficient. These devices are characterized by the speed of firing flashes, as they do not release all the charge unless the subject is very far away, and the closer the subject is and the pupil of the lens used. The wider the blinking rate, the higher the rate. This type can be used while using a motor on the camera to give up to 5 flashes per second. These devices can also be used manually, and the light is calculated from a computer on the flash or from the index number.

Devices dedicated to a specific camera: These are the newest types. Every company that produces a camera has its own flash that works with it. In many cases, the flash is the same as the previous type, but the fully charged bulb, as well as the sufficient light confirmation bulb, can be seen through the viewfinder of the camera. In some cases, when the dedicated flash is installed on the camera, the appropriate shutter speed is automatically determined on the camera to prevent errors.
. In some types of cameras that measure exposure by light falling on the film during exposure, the camera controls the flash and stops firing the rest of its charge when a sufficient amount of light reaches the film. And this is because whatever the type of lens or whatever type of filter is in front of the lens, all of this will be taken into account automatically when photographing with a great advantage of the lens or the extension on which the flash is extended.

Special flash devices: such as:

(A) The ring flash whose valve is installed around the lens to give illumination without shadows when shooting close-up (macro). (B) A flash with two diodes, one of which is variable in angle and the other is fixed to the front, and helps in portrait photography
Guide Number: This number is found in the instruction booklet attached to the flash. This number changes with the speed of the film, but it was written in relation to the speed of the film: 100 ISO per meter

The lens aperture required for each distance is calculated as follows:

- The shutter speed is set according to the instructions given by the camera maker, and it is often less than - a second for focal plane shutter cameras.

(p and p).

2- Required pupillary aperture:

The index number

Palm distance

For example: -

F3,2 =

And rounding this number to Roche is done in the lens - 3.5 or 24 in the case

No guide number.

Calibration work as follows:

We put 100 ISO film in the camera

What is required to be photographed at a specific distance, let it be 3 meters. We photograph the lens apertures from the smallest to the largest using the subject:

4 Acid the film and we see the best image in terms of lighting. If the best image, for example, was with the F8 aperture

... index number = 3 meters x 8 = 24 for a film with a speed of 100 ISO.