Waterscreen
Waterscreen refers to projection surfaces made of water, as seen at the opening event of the 2004 Olympic Games in Athens . The term waterscreen, or water screen separately, has established itself colloquially in event technology in general for water projection surfaces, especially in the English-speaking world. When the press often talks about the projection of holograms , in most cases it is a projection onto a waterscreen, although technically this has nothing in common with holography , but only creates an effect that is generally established as a hologram projection seems to be.
Basic principle
A waterscreen creates a water surface that is as homogeneous as possible and as thin as possible (and therefore as transparent as possible ), which is suitable for projecting laser graphics , videos , slides or gobos from spotlights. Due to the optical characteristics of the water, an image projected onto the water surface from behind is visible in a dark environment. If the viewer looks from the direction of the projector, the image can hardly be seen on the waterscreen. The waterscreen must therefore be placed between the projector and the viewer so that a visually satisfactory result can be achieved (rear projection). Due to the high transparency of the water, only the projected image is visible under optimal conditions. The motif shown seems to float in the air like a hologram. The less water there is in the air for projection, the stronger the projection source must be, but the more three- dimensional the projection appears, since in this case the water itself is hardly illuminated by scattered light from the surroundings. Naturally, the best result can be achieved with laser graphics, since the high intensity of the projection requires little water for a sufficiently high-contrast representation.
Construction principles
Waterscreens are available in various designs that are used depending on the technical and local conditions.
Water screen curtain
Water distribution segments, similar to an elongated shower head, create a spatially limited waterfall or water curtain . The falling water is caught in a basin and transported back up using a pump . The advantage of this principle is the homogeneous spread of water and the low level of splashing water, which is why this variant is mainly used indoors. This type of canvas is increasingly being used as a wall element made of water outside of its original area of application for trade fair construction and interior design . Decisive for the quality of a curtain waterscreen are the number of nozzles per running meter , the design of the nozzles (with regard to the absence of splashing water), the homogeneous water distribution within the distribution segment, the weight of the construction, the maintainability (e.g. cleaning of the nozzles), the pump technology used and the material properties of the water distribution segments. For mobile applications, distribution segments made of aluminum are mostly used due to the transport weight, handling and hanging load . In stationary use, water screens made of stainless steel have proven more effective.
Jet water screen
In this case, the water distribution segments are installed in a basin and, compared to the Waterscreen Curtain, create a wall of water from a row of water fountains with significantly fewer nozzles per running meter . Due to the formation of splashing water, this principle is almost only suitable for outdoors, but is very well suited for video playback due to the large amount of water in the air and the rectangular shape. The disadvantage is the relatively great depth of the water surface, which makes particularly filigree image content more difficult to see.
Spray water screen
With this design principle, several pumps often jointly generate a water jet that is directed onto an impact surface . Similar to a spoon under the tap, the water spreads out as a thin film in a semicircle upwards and to the side. This water film can be used for projection. The advantage of this type of construction is the low infrastructural effort (neither hanging scaffolding nor a flat surface is required) and the possibility of being able to operate the Waterscreen floating with little additional effort. Disadvantages are the high sensitivity to wind, the extreme formation of splashing water and the semicircular shape, which can usually only optimally display content specially prepared for this shape. In the case of video, which usually shows rectangular content, either only a small area of the available area can be used or a lot of image content is lost due to the semicircular shape (usually more than 50%). In addition, the projection surface produced is very inhomogeneous. While even finer details are still clearly recognizable in the direct vicinity of the outlet nozzle , the clarity of the projection towards the edge of the waterscreen decreases very quickly. Nevertheless, this design principle has established itself on a broad basis due to its easy handling in outdoor use.
Related techniques
Fog canvases
For many years, various manufacturers have been trying to transfer the principle of the waterscreen to the construction of a smoke screen. So far, this technology has not yet been able to establish itself on a broad basis. The fundamental problem is the low mass inertia of water fog compared to water droplets, whereby even the slightest turbulence in the air leads to the projection surface tearing off. The Scandinavian manufacturer Fog Screen , well known in the press, has a corresponding product on the market. The relatively high price, the effectively usable drop height of the fog of hardly more than a meter as well as the disproportion between technical construction and usable area, however, make this product at best a niche existence. Similar systems are now also available from Germany, China and the USA. A product from the German manufacturer watershow.de enables projections up to 8 m in height for the first time.
Water fountains
A cost-effective alternative to waterscreens, which is technically subject to major compromises, is projection into a fountain arch. The water mist falling from the fountains is extremely inhomogeneous, extremely susceptible to wind and is only suitable for projecting laser graphics.
Watergraphic
Writing water wall / Watergraphic creates any images and fonts from water. Individual water jets are switched on and off very quickly under computer control. With the appropriate control technology, it is possible to display contrast images (black / white = no water / water). These fall inexorably downwards according to their initial speed and mass according to the acceleration factor.
gauze
In stage and theater technology, semi- transparent gauze fabrics have established themselves as a cost-effective solution for generating spatial projections. Normal gauze fabric is more suitable for front projection with common media, but this usually means that the projected image is shown again on the stage background. Only specially coated fabrics are suitable for rear projection, but in this case the light intensity of the projection decreases very quickly based on the direct line of sight between the viewer and the projector (so-called hotspot effect). The decisive disadvantage compared to waterscreens is the fact that the screen always remains recognizable as such, even under optimal conditions. While waterscreens are suddenly there and quickly gone as if by magic, with a gauze it is inevitable that the viewer recognizes that a screen is appearing.
trademark
The term Water Screen is also a registered trademark of LOBO electronic GmbH for such projectors.
