Stereoptics: a 3D-OSA
Universidad de Valladolid Physics League
‘Stereoptics: a 3D-OSA’ was born as an attempt to make an interactive and attractive workshop to show different ideas: stereoscopic vision, linear and circular polarization, and 3D-cinema technologies. With this main target, we developed a workshop where different notions were explained in order to build a whole story about light perception, visual optics and polarization. We divided the workshop in two parts - first was an introduction of the main notions and the second part was the construction of a 3D projection system of photo and video.
First we explained how both eyes got the ‘same’ visual stimuli with a fixed separation between them. With that information the human brain is able to merge the images from each eye in a 3D panorama with depth perception. To illustrate this idea, the first experiment performed was the ‘Pulfrich effect’, where, placing a neutral filter over one eye, a lateral movement (left-right) seems to move in depth. With this effect we demonstrated the importance of receiving the same information in both eyes in order to obtain a correct depth impression.
The next step was to show what the polarization of light is. We can load an image on a computer monitor with no polarizing filter. If we do not place a linear polarizing filter over the screen, the image cannot be seen. Furthermore, rotating the linear polarizing filter also rotates the polarization of light, changing the combination of colors we perceive in the image shown. At this point, the idea of total extinction can be illustrated by the placement of a second linear polarizing filter over the first one, forming a 90º angle with it.
After that we used two pairs of 3D cinema glasses to approach the concept of circular polarization. We asked for two volunteers to put on the glasses, look at each other and wink alternatively. The result was that they can see through one of the eyeglasses while the other one appears dark. This happens because of the l/4 plate placed in the crystals with different orientations: while one allows the light to pass, in the other one the l/4 plate gets the total extinction phenomenon.
Once the introductive part of the workshop ended, the participants of the workshop were invited to enter the ‘Physics League Cinema’. In that cinema, two projectors were separated a well-calculated distance, so that the two images they produced overlapped on a silvered screen. In front of the lens of both projectors we place a combination of a linear polarizing filter plus a l/4 plate, in order to have circularly polarized light coming from both projectors; of course, each of them turns in a different sense. The silvered plate allows to keep these polarizations intact after reflecting in the screen, reaching the observers properly.
Having each of the participants a pair of 3D cinema glasses, two different images (a castle and a statue) were projected on the screen. They were asked, once more, to wink using alternatively each eye, so that they could check again the total extinction phenomena happening in each eye with one of the images. After that, some images were shown to let the public enjoy the effect. Finally, we showed a 3D video recorded at the beginning of the workshop and processed during it.
This workshop has been performed during some activities of Universidad de Valladolid Physics League chapter. The debut was in the European Researchers Night at the Science Museum of Valladolid with 2000 viewers. It was also performed completely during the Science Week in November at the Science Faculty of the University of Valladolid, being part of our successful workshop “Game of Physics”, where we had an audience of 300 students from the Castile and León region. Furthermore, Stereoptics was adapted to fit in our educational theater play “Scary Physics” performed at the Castle of Portillo (150 viewers) and at the Science Museum of Valladolid during Halloween (600 viewers). In total, 3050 people have enjoyed the workshop.
The Centennial Special Events Grant awarded that helped to build ‘Stereoptics: a 3D-OSA’ was a challenge for all the members of our chapter. Although one of the members had a previous idea of how this could be reached, most of us had never tried to build a system of these characteristics. Even the estimation of a budget was difficult to handle, because we were not used to most of the needed materials. Also, finding and buying them required in most cases more time and attention than we expected.
In the preparation of this project, we have learned a lot about some different topics: visual optics, psychophysical perceptions, polarization of light and the use of some software to process the images properly. Building the system and reaching an optimum quality of the 3D images were not easy tasks, but we did not give up at any moment. And of course, the expectation and excitement to carry out the workshop in different ambiances have provided a lot of good moments working together. For all of us, the project ‘Stereoptics: a 3D-OSA’ has been encouraging and challenging, and the good opinions we have received have given us a very positive vision of our work. Thank you OSA for awarding us the Centennial Special Events Grant - check out our Happy Birthday Shout to OSA here.
