With passive 3D stereo we use two projectors which project both the left and the right image at the same time. We achieve the ability to deliver two different pictures to the two different eyes of the spectator using polarization technology. Here’s how we can ensure that we deliver the correct picture to the correct eye only: For example, we put a polarization filter next to the lens of the projector showing the picture for the left eye and use the same polarization filter for the left eye in the special 3D glasses. In this way we can project two pictures with different polarizations onto the same screen at the same time with the 3D glasses only letting through the correct picture for the left and right eye, respectively. Obviously, we have to ensure that the screen itself is non polarizing and reflects the maximum amount of light (because polarization has an impact on the brightness of the picture). For both reasons a sliver screen is necessary.


The disadvantage of passive 3D stereo is that polarization filters reduce the brightness of the picture. In general, we talk about a high transmission if a polarization filter lets through a lot of light. The higher the transmission of the filter, the brighter the resulting picture and the cheaper the required projector to achieve a specific picture quality will be. The best visual results are usually achieved with LCD-projectors in combination with high transmission filters like our 3D-SPAR.

Passive 3D stereo works both as front and rear projection. In both cases, selecting the right components has a huge impact on the quality and the cost of the 3D solution. For front projection a special silver screen is necessary (like our awater 3D Stereo Screen). For rear projection, rear projection foils required. Note that foils are usually easier to handle and transport.

Passiv 3D stereo does not work with conventional screens. Because conventional screens usually de-polarize the visual information, they mash the two distinct pictures and thus cannot properly deliver the correct picture to the correct eye. The visual effect of this complication is the so-called “ghosting”.


The benefits of passive 3D stereo include:

• Simple and cost effective system
  
• Best channel splitting
  
  
• Don’t put stress on the spectators eyes and are suitable also for longer projections.
  

The disadvantages of passive 3D stereo:

• Loss of brightness through polarization filters
  
• Non-depolarizing silver screen is necessary for front projection
  
• Non-depolarizing rear projection screen or rear projection fabric is needed for rear projection