With front projection the picture is projected onto a reflecting wall. The viewer sits on the same side as the projector.
With rear projection the picture is projected onto a transparent screen. The viewer sits on the other side.
Only the HoloPro™ Mirror Screen has a front projection system. All the other HoloPro™ systems are only suitable for rear projection.
Key words: projection ratio, keystone/trapezium correction, ANSI lumen
The projection ratio indicates the ratio of the picture width to the projection distance. Almost every beamer has different lenses. In order to know how far the projector has to be set up from the screen for a given screen width, the projection ratio must be known.
Example: the projection ratio is 2:1, i.e. the beamer must be set up at a distance that is twice the picture width. If the picture width is 2m, the beamer must be set up at a distance of 4 m from the screen.
HoloProTM is designed so that a projection ratio of approx. 1.8:1 must be adhered to. So in order to generate a 1m-wide screen, the projector must be positioned at a distance of 1.8m.
A keystone is the distortion of a projected image that arises when the projector is positioned diagonally to the projection area. This trapezium-shaped distortion can be corrected either by moving the lenses parallel to the screen (lens shift) or by electronic correction.
HoloProTM is illuminated by the projector at an angle of 37°. For this reason, the projector must have a vertical trapezium correction of +/- 30°.
The illuminosity or illumination intensity of projectors and beamers is given in ANSI lumen. The larger the projection surface is, the higher the illumination intensity of the beamer has to be.
Here are some recommendations for different sizes of HoloPro™ screens:
HoloPro™ is offered as standard in 4:3 and 16:9 in the following formats:
In addition, special formats of up to a maximum height of 1.60 m can be manufactured.
HoloPro™ is produced as standard in landscape format, 4:3 and 16:9.
Any landscape format can simply be turned 90° to create a portrait format.
But the angle of visibility will change for the viewer!
This means ±15° horizontally and ±45° vertically.
In addition, the projector must also be turned on its side (90°) so that the full resolution can be displayed. But this can only be done with very few projectors.
A larger landscape format (e.g. 55") is cut down into a portrait format (40"). In this case the angel of visibility for the viewer is maintained.But the same problems remain as with the first possibility: if the projector cannot project laterally only a section can be shown.
HoloPro™ must be protected from dampness. For this reason HoloPro™ is supplied in glass, plastic or laminated foil.
Embedding in glass is the best protection for the foil. It is not only protected against damp, but also against mechanical damage such as scratches. The foil is embedded in composite safety glass. Low-reflection glass is also used. The non-mirrored Schott AMIRAN glass has a reflectance of only 1 %. Any possible ambient reflections on the glass are virtually zero.
Acrylic glass (synthetic, glass-like plastic):
Embedding in acrylic glass is an easier and splinter-free alternative to glass. Acrylic glass screens have a long life on account of their good resistance to weather and are also resistant to frost and heat. They also have excellent brightness and high transparency. For these reasons, this version of embedding is popular in shop window applications.
If HoloPro™ is laminated in foil, it can be affixed to existing glass surfaces with the help of adhesives or double-sided transparent adhesive tape. It is intended for inside use. Continuous high air humidity on the surface can disturb the holographic function.
HoloPro™ cannot be hung on a wall. Because it is rear projection technology there must be room for the projector behind it.
But there is a version with embedded mirror foil (mirror screen). Here, front projection is possible. It can therefore also be hung up on a wall. The same projection and viewing distances apply. But it is then no longer transparent.
Objects are played via a projector. Laptops, computers, DVD players or (for TV reception) a DVB-T receiver can be used as sources. Pictures and videos can be shown.
The entire projection area is made up of many individual Holographic Optical Elements (HOE); several million HOEs are imprinted per square metre of film material.
Each individual HOE contains information on how the light coming from the projector should be diverted to the viewer from its precise position.
Here, only the light coming exactly from the direction of the projector would be diverted to the viewer. All other light is ignored and passes though the screen.
HoloPro™ is therefore an angular-selective system.
To maintain the attractive appearance of the HoloPro™ screens they must be cleaned regularly. Normal dirt can be removed in the normal way with water, a sponge, a rag and wiper or wash leather.
In our experience, it is best to use a 1:1 mixture of alcohol and distilled water with a drop of detergent. The latter should be neutral surface active agents without any scouring agents (e.g. Pril, Ajax, glass cleaners, Sidolin glass cleaner, spiritus or similar). In order to avoid cleaning marks the cleaner should only be applied in diluted form.
Any heavily alkaline suds and acids, especially fluoric acids or detergents containing fluoride attack the non-mirrored glass surfaces and lead to irreparable burn damage. Coarse cleaners such as scourers, wire wool or materials with course metal threads are unsuitable, as are materials containing silicon.
Do not use blades! Using steel blades could cause scratches in the laminated glass surface.
Should these cleaning instructions not be adhered to, the supplier will assume neither guarantee nor liability.
A hot spot is a place on the picture whose brightness far exceeds the average.
There are no hot spots with HoloPro™ because the projector is not on the same axis as the viewer. It therefore does not "look" into the objective of the projector.
HoloPro™ is a rear-projection medium. That means that illumination is from behind and the viewer stands in front of the projection screen.
Viewing position and distance:
The visibility of HoloPro™ is ±45° horizontally and ±15° vertically.
Depending on the size of the screen used, there are several possible viewing distances:
How high must the HoloPro™ screen be hung up?
As a condition of the vertical visibility of ±15°, the centre of the picture on the screen should be positioned at a height of 1.65 m. This corresponds roughly to the average human height.
Position of the projector:
HoloPro™ is designed so that illumination by the projector takes place at an angle of approx. 36°. It does not matter whether the projection takes place from above or below (the HoloPro™ screen simply has to be turned around accordingly).
Projector geometry using a 50" screen as an example:
The larger the illuminated surface is, the further away the projector has to be positioned.
At what time of day should the application be run?
How long does the application run during the day?
Which direction does the shop window face?
Is the window covered by an awning or canopy?
Is the glass tinted and can this tinting/colouring be removed?
How intense is the sunlight in your geographical area?
The answers to these questions determine both the size of the shop window application and the ANSI lumen strength of the projector used.
If the display application is to be used for more than 4-5 hours per day, then only a DLP projector can be used. LCD projectors are not suited to daily use over periods of several hours. There will be technical problems with the projector after a year at the latest otherwise.
So if only a DLP projector is possible on account of the time of use, then the size of the display must also be limited for the sake of economic viability. There are only affordable DLP projectors available up to 3500 ANSI lumen. If one assumes approx. 0.5 lumen per cm2, the largest display that can be used is 60" maximum.
Ideally, the window should face north and not be subjected to sunrises or sunsets or with sun from the south during the winter months.
There will be massive differences in the projected display size and the ANSI lumen number of the projector between a shaded window facing north and an uncovered window facing west.
If the window glass is tinted and the tinting cannot be removed, it is very unlikely that you will be able to set up a shop window application.
Another problem is blinding light and reflections. Any display system based on glass has these points to contend with. Although there are anti-reflection foils, you must remember that the more layers the projector light has to penetrate, the less light gets through to the other side.
The resolution of HoloPro™ depends on the projector used.
The HoloPro™ holographic optical elements have a direction characteristic.
Each HoloPro™ screen has a cut in the hologram on one of the four corners of the film. The missing corner prescribes the direction in which the screen must be positioned when being assembled:
Projection from below: Missing corner top left from the viewer's position
Projection from above: Missing corner bottom right from the viewer's position
For a successful, i.e. bright and colour-neutral projection, adhering strictly to the prescribed geometry is crucial. Any deviations from the prescribed geometry will lead to loss of brightness and colour neutrality may, in certain circumstances, no longer be guaranteed.