تجهيزات خاصة - ١ - اختيار واستخدام المواد .. كتاب التصوير الضوئي

Special Equipment - 1 - Selection and Use of Materials .. Book of Photography

Selection and Use of Materials
Special Equipment

Panoramic Machine:

This type of machine is used to photograph groups of people, landscapes or interior scenes. The film is usually 35 mm but is used at a length of 60 mm. The film is applied to a semi-cylindrical frame and the lens rotates while taking the picture. Thus, the picture covers a large horizontal field angle close to 140°.

This lens is of a simple optical formula that is less expensive than a true wide-angle lens formula.

To take pictures, the machine must be held completely horizontally because any tilt gives an unbalanced view of the picture. In any case, the machine contains a balance (water level) and unfortunately it is not always visible in the scope. The support cannot be dispensed with for normal use of the machine, especially if it is a matter of scenes representing buildings. For moving subjects, special precautions must be taken: if the subject moves in the same direction as the rotation of the lens, it appears stretched, but if it moves in the opposite direction, it appears compressed.

(Panoramic device )
(We see the lens that rotates to give an extended view with a wide horizontal field at the bottom. An interior view taken with this device. Note the slight distortions towards the edges of the image if we compare it to the image provided by a wide-angle lens.)

(Bosemeter selects exposure areas
This bosometer measures at a very narrow angle in the middle of the field it is aimed at. We can thus measure the exposure value on a very small area of ​​the subject, but its use requires a systematic selection of the areas to be measured.)

- Spot meter:

The spot meter allows us to obtain correct exposure values ​​for a very small area of ​​the subject. The optical device equipped with it measures the lighting at a very narrow angle. The optical collimator gives a field close to 200, for example, while the central area of ​​measurement is only 30° or less. The spot meter scales are very wide: for example from F/1, F/128 for apertures and from 6 to ASA 6400 for speeds. These scales are illuminated to allow them to be read in low light.

The advantage of the spot meter lies in the selection and accuracy of the exposure measurement. On the other hand, it is necessary to know the difference between the exposure measured locally and what should be the overall exposure that gives a correct image of the whole subject. The measurement obtained for the shadows is often compared with the measurement obtained for the high lights and then taken. This principle allows to avoid parts of the subject with an average value (background - sky, etc.) that could distort the instructions of the bosometer that measures the overall exposure.

- The double-bracket for stereoscopy:

It is attached to the normal lens of most 24 x 36 mm machines. It consists of two sets of mirrors spaced apart with the same distance between the eyes. It divides the light entering the lens into two beams (see the drawing) and forms two images, each with a different point of view. Below is an example of a stereoscopic pair of images.

- Preparation for stereoscopy:

Stereoscope (stereoscope) The two positive images mounted side by side are examined through the two eyes of this scope. The model shown here is the simplest.

- Images for seeing in three dimensions:

A stereoscope has two lenses spaced as far apart as our two eyes. They produce a pair of slightly different images that, when combined, produce a re-emphasis. To obtain this emphasis, the images must be selected with a stereoscope or with a special device for displaying on a screen. There is a simpler and less expensive principle that uses the double band that you attach to the normal lens of a 24 × 36 machine. The two images are recorded side by side on the same 24 × 36 size: they are slightly different because of the distance between the two points of view. The feeling of emphases is returned by examining the pairs of views in the stereoscope.