 Minimizing projection depth and choosing the right mirror types. |
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By Greg Jeffreys Director Paradigm Audio Visual Ltd |
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How
can I minimise the projection depth?
It’s all done
with mirrors! By using one, two, or even three mirrors, the rearpro installation
can be made very compact.
There are two invaluable tools available on the Internet. On www.dnp.dk (dnp’s web site) in the Toolbox, you will find a dynamic calculator where you can enter your lens type and your screen size and you will then be given the theoretical minimum depths required using mirrors – plus a drawing that you can copy/paste into other documents. On www.rearpro.com (Paradigm’s web site) in the Rigs section, you will find tables that give conservative rig dimensions for all screen sizes – plus conservative budget prices.
It’s all done with mirrors – glass or foil?
Mirrors used in rearpro applications must be front surfaced. Conventional ‘bathroom’ type mirrors will cause visual artefacts, as the light has to go through the glass before hitting the reflective surface and then back out through the glass, refracting both inwards and outwards.
Front-surfaced mirrors obviate the problems illustrated above, as the reflective layer is on the surface, as the name implies. They are also known as ‘first surface’ and ‘front-surfaced’ mirrors. There are two choices for front-surfaced mirrors: glass and foil. Both are used widely. In theory both offer similar qualities.
Although we sell and use both types, in practice, we prefer glass mirrors. They have slightly higher reflectivity in most cases (90-94%) than foil (86/87%, typically). Also the surface is perfectly flat. But, if a large mirror has to be angled forward, often its mass can cause it to deflect under its own weight. This means that for most rigs we use glass, but larger rigs often have foil mirrors – sometimes for safety and handling reasons. Remember that these are large, heavy pieces of glass that can be dangerous if not handled properly. The subject of mirrors is a complex one, and subject to personal preference. The views stated here have been generated more by practical commercial experience than by theory alone.
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There are two invaluable tools available on the Internet. On www.dnp.dk (dnp’s web site) in the Toolbox, you will find a dynamic calculator where you can enter your lens type and your screen size and you will then be given the theoretical minimum depths required using mirrors – plus a drawing that you can copy/paste into other documents. On www.rearpro.com (Paradigm’s web site) in the Rigs section, you will find tables that give conservative rig dimensions for all screen sizes – plus conservative budget prices.
It’s all done with mirrors – glass or foil?
Mirrors used in rearpro applications must be front surfaced. Conventional ‘bathroom’ type mirrors will cause visual artefacts, as the light has to go through the glass before hitting the reflective surface and then back out through the glass, refracting both inwards and outwards.
Front-surfaced mirrors obviate the problems illustrated above, as the reflective layer is on the surface, as the name implies. They are also known as ‘first surface’ and ‘front-surfaced’ mirrors. There are two choices for front-surfaced mirrors: glass and foil. Both are used widely. In theory both offer similar qualities.
Although we sell and use both types, in practice, we prefer glass mirrors. They have slightly higher reflectivity in most cases (90-94%) than foil (86/87%, typically). Also the surface is perfectly flat. But, if a large mirror has to be angled forward, often its mass can cause it to deflect under its own weight. This means that for most rigs we use glass, but larger rigs often have foil mirrors – sometimes for safety and handling reasons. Remember that these are large, heavy pieces of glass that can be dangerous if not handled properly. The subject of mirrors is a complex one, and subject to personal preference. The views stated here have been generated more by practical commercial experience than by theory alone.
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