Opaque projector

The periscope, (Greek: to see it, look; Synonyms: Antiskop, Paxiskop, wall projector ) is an optical device for projecting primarily opaque media. The original is illuminated and the diffusely reflected light via a mirror through a lens onto the screen - colloquially Canvas - projected. Episcopes belong to the family of projectors and operate on the principle of the direct front, which is why they are referred to in today's parlance as incident light projectors.

Operation

Classic Episkop Leitz

Classic Episkop of Henry Malinski

Modern Episkop the company Enna ( original is placed on the unit above)

School periscope, original surface 16cm (upright A4, be traversed ) x 19cm,

With a periscope opaque flat objects, images or pictures are projected from books onto a screen. The periscope consists of a support surface for the submission, an illumination system for illuminating this template and an objective. In general, a deflection mirror is fitted in front of or behind the lens, which directs the beam onto the vertical wall.

The lighting system is to illuminate the document and uniformly with high illuminance. Here a steep light enhances the effect. However compete smooth, shiny surfaces, such as glossy art paper, reflections on entering directly into the lens and then appear as light spots on the projected image and reduce the contrast ( readability). Of the variation of the angle of incidence of illumination, these reflections can be reduced.

Boost allows the illuminance on the template through the use of a concave mirror behind the lamp and a condenser lens ( convex lens ) between the lamp and template. Aufhellspiegel on the sides of the support surface to support pooling addition. Thus, the light is better focused on the presentation and the luminous flux of the lamp is better used.

For the projection beam path only the small amount of light diffusely reflected from the template can be used, which radiates toward the lens. The rest is lost and can not be used for image formation. However, the quality of the lens, its diameter or its aperture ratio affects the intensity of the projected image on the screen crucial. The mirror directs the light from the horizontal to the vertical template screen. Without the mirror, the image would be displayed mirrored or mirror image.

In Episkoposes with larger template surfaces are lighting systems with lamps that have a long light field, such as halogen floodlight lamps or metal halide lamps, Liesegang Episkop E10, or more reflector lamps, Instant Presenter plus, VEGA International doo uses. By this arrangement, the template can be stronger and more evenly illuminated.

Designs

The different types of bishops are based on original surface and application areas. Small episcopes with a document area, which is about the size of a postcard, are used more for home use. The original is placed in these devices usually on top of the template field.

Episcopes for school use have a template area of ​​about 19 ​​cm across and 16 cm high. This allows A4 originals are on edge projected into different sections, Leitz Episkop LE 19, Liesegang Episkop E11-522/260. The projected image is easy to read on a screen of approximately 1.8 m by almost 10 -fold magnification. The illuminance on the screen shows a contrast that still allows, depending on the room light has a good visibility.

Large units with a document area to 30 cm x 30 cm give a good overview of large templates such as maps, prints, designs etc. The Overview at the expense of readability, as only a 5 on the same screen - magnification is achieved.

For many devices there are designs in which the presentation of a document holder from below the original surface is pressed. If the original holder is removable, the projector can also be placed directly on a great template. For some major units, the template can also be placed on top of the original surface. Modern episcopes have a so-called break lamp, not to dazzle the user in the target change. Once the Document Cover is opened, the strong projection lamp turns off and a weaker lamp.

A special type is the Antiskop as character Episkop. The projector is adjustably mounted on a vertical column and projected on a drafting table. The magnification can be easily and more set depending on the distance from 0.5 to 10.

Combinations as Episkop and slide projector are called epidiascopes.

Benefits

Because of the direct front, templates can be projected by bishops (with restrictions) non-transparent as well as transparent. The originals must not be previously worked only for the projection, ie is copied in a transparent media, and, if desired, to a specific format, such as during daylight hours or slide projectors. Possible originals for direct projection, for example: photos, pictures, documents, materials, inlays and more. The best results are achieved with matt possible templates. A plane mirror on the template surface results on the screen only a dark field. When using transparent media (not too tight), it is sufficient as a compromise, to provide them with a white matte surface and insert into the periscope. With modern bishops can a template to a size of 1.6 × 1.6 m and larger, depending on the room light are projected onto a screen.

Disadvantages

Due to the small proportion of the diffuse reflection which is reflected toward the lens, must be used as opposed to the rear projection lamps with high power. Previously the necessary power could only be provided by arc lamps, which made the devices large and unwieldy. With the development of halogen projection lamps and metal vapor lamps with a higher light output per watt, the devices were a little bulky, but the enormous heat that was still a problem. Thus, the housing of the heat could withstand episcopes were predominantly made ​​with a metal housing. Also, a fan was sufficient active cooling system, necessary. With the development and deployment of low-voltage halogen projection lamps the heat problem could be reduced by some, as by the use of two projection lamps, which (usually from above and below ) illuminate the presentation of two sides. The housings were so compact and could be made of lighter plastic, which the device could be much handier. The cooling system could also be throttled in the performance and the noise level can be lowered during operation. Moreover, it was reduced to the original by infrared transmissive mirror behind the lamp and infrared blocking filter between template and lamp parts of the thermal radiation. The load on the submission by the extremely high illuminance in conjunction with the temperatures should be considered in order to avoid damage to sensitive documents. Other disadvantages arise from the nature of the template. This should be very dull, colorful and rich in contrast because of the direct front to get a good projection image. Furthermore, no changes to the template, such as marks on text passages, the inclusion of graphics, etc. can be made during projection. For this, the template must be removed and then reinserted. The process of change can not be tracked on the screen as opposed to overhead projectors.

Developments

A further development of periscopes provide the so-called Visualizer dar. In the operation they differ significantly from the classical projection of the periscopes. With the Visualizer, as with a periscope, any kind of material (books, photographs, three-dimensional objects, etc.) are recorded by a camera or scanner and then he delivers a high resolution image, for example, to a video projector.

The modern version of the periscopes is the Instant Presenter, but is also about 20 kg.

Use

In the school lessons or presentations episcopes be little or no longer used. Displaces they were of the easier -to-use overhead projectors, which can be changes to the template better track and are therefore suitable much better for teaching and presentation purposes. Due to the availability of non-transparent templates episcopes are popular among painters, artists and copyists. They are used to advance or by drawing sketches, drawings, photos, etc. for some time to come episcopes even with airbrush artists often used. Some build it to also to the projector.