Optics with Jello Lenses

How do you see light’s path through a lens?  We did this experiment at the DAMOP teacher’s workshop at Penn State last year.  Make Jello in a flat bottom pan, about 3/4″ deep.  Use half the water so the Jello is firmer than normal.  You’ll have to experiment with the color and tell me which works best, I haven’t done this on my own yet.

Obviously the Jello is made the day before.  Now cut the Jello into the shapes of the lenses.  You can make prisms, double concave, convex, whatever you like.  You can float the pan in warm water to release the lenses from the pan.  Don’t do it too long, just enough for the Jello to lift out undamaged.

Now shine a laser pointer through the Jello.  You will be able to see the path of the laser and follow as the light is bent by the lens.  Set up a series of lenses and have fun.  When you are done, you can eat the experiment.

IMAX Glasses and Polarized Light

I was just at the IMAX this week on a school trip and I asked to keep two pairs of the glasses for my classroom. I asked. I’m not one to steal, even something like these inexpensive 3D glasses.

The way IMAX creates 3D is by polarizing the image on the screen so that light for the left eye is 90° out of phase with the light for the right eye. You can easily demonstrate this by first placing the glasses over top of one another, left lens over left lens. You can clearly see through both the doubled left and right lenses as in the picture on the right. The picture below shows the left lens of the front glasses over the right lens of the rear pair. The middle lens pair is black. You can click on these images to get a full size view.

Now turn one pair of glasses 90° to the other and cover the left lens with the rotated left lens. The glasses are now dark. Move the rotated left lens over the right lens and the image is clear again. Now repeat this with the right lens from the beginning. Clearly the left and right lens are out of phase.

I’m not sure how they create this image on the screen. My best guess is that they have a dual projection system that goes through similarly polarized filters. I believe that the separation distances are going to generate the depth. If someone knows for certain, please post the details.