أجهزة العرض .. كتاب التحميض والطبع والتكبير

Projectors:

Projectors are generally divided into the following three main types:

(a) Devices for displaying opaque images, such as photographs on paper, pictures printed in books, or geometric shapes...etc. Film strips, slides, or movie screenings. By means of this type, images are viewed by means of rays that are penetrated by Transmitted light, and this type of display devices is known as Reflected Rays of Images (Fig. 101).

(b) Devices for displaying transparent images, which are used in displaying Diascope tapes.

(H) There are projectors that combine the two previous purposes and are known as Epidiascopes. They may be of the first type designed to display opaque images, with additional parts installed on them to prepare them for the second hypothesis as well, which is displaying transparent images.

Positive transparent image display devices, in turn, are divided into two main types.

(a) Ciné projectors, the study of which is outside the subject of this book, and therefore it suffices in this respect with what came in Figures 102 and 10, to show the optical system in some of its types, merely knowing the difference between it and the optical system in the second type. whose study is included in the subject of this book.

(B) Slide Projectors: This type also includes those devices that are prepared for displaying short film tapes, as the optical system does not differ in the two cases, except that the latter case requires that the display device include a means of carrying and wrapping the short film. This is usually done by adding two spools to the projector, one of which holds the screen, and the second receives the displayed images (Fig. 108, p. 398).

35mm transparent photo slide projectors:
35 mm. Slide Projectors

These devices consist of the following main parts:

(a) The lamp house contains a source of light.

(b) A light condenser, or sometimes more than one condenser

(h) Slide Carrier

(d) Projection Lens

It is customary to place behind the lamp a reflective concave mirror, the purpose of which is to form an image of the lamp filament, and thus both the filament and its adjacent image ensure that the light source is flat (Fig. In addition to the presence of the filament image, it increases the brightness of the image when it is displayed. It is also usual for the projector’s side condenser to consist of two lenses and a Plano Convex (Fig. 104), but due to the resulting spherical aberration defect that causes a decrease in light energy Which is used to illuminate the image, so the two Plano Convex lenses are replaced by an aspherical lens that is placed directly in front of the light source (Fig. 104).

If some projectors (which have low-power lamps) may not have any means of ventilation, but if the power of the lamp is increased (to 300 watts, for example), then the device must be provided with a means of ventilation (such as an electric fan) so that the image or the lamp glass will not be affected by the high temperature. Heat, and to help prevent heat from being projected, a heat absorbing filter is placed between the lamp and the negative (as shown in Figure 104).

The maximum apertures of the projector lenses differ from each other, as they may be 1.9 4, or less than that to 3.5, or less than that sometimes. The area of ​​the image displayed on the screen is affected - to a large extent - by the focal length of the lens, so its area increases as the focal length becomes shorter. A lens whose focal length is 80 millimeters is sufficient to make the image width 90 cm. The width is about seven feet. The width of the image remains 90 cm as well if the focal length of the lens is 100 mm, with an increase in the screen distance to nine feet. From the foregoing, it is clear that if the showroom is long, a lens with a long focal length must be used, and therefore lenses whose focal length sometimes reaches 250 millimeters are prepared to face such a situation.
Most display devices have a way to raise or lower the device so that the image falls on the display screen, and this is usually done by means of large eraser screws (Fig. 106).