Improvised 3D glasses

A while ago I made my son a red filter from a cheese wrapper to show how it blocks all colours (wavelengths) of visible light except for red, and I used this to make a phonics practice activity.  I also made a blue filter from some of the film that covered a new mirror (you can also buy blue cellophane or acetate which is probably better, but I used what we had) and I was intending to do a similar activity, but ended up doing something different...

We were talking about seeing things at a distance, and I decided to try and show him a bit about how our eyes work together to help us figure out how far away things are.  I'm not entirely sure that the explanation worked, but we had fun with some improvised 3D glasses and we can always talk about the science again another time!

A few years ago (ok, it's probably more like decades...) 3D anaglyph films where you wore glasses with one red and one blue filter were popular.  These work because the film has two pictures in each frame, one with blue hues and one red, and each eye sees one of these when viewed through the glasses as the filters block the other.  Your brain then interprets the image as showing depth/distance even though the screen you are viewing them on is flat.  Normally when objects are at a distance, your eyes see slightly different images because they are a small distance apart, and the brain interprets this to give you distance perception.

I first showed my son a still image I'd created using an online tool.  Ideally I'd have two photos taken from a distance apart to make the composite red/blue image, but I didn't plan far enough ahead to have set this up so I just used a tool that tries to recreate the effect from a single image.  My image is below (you need the left eye to be red and the right to be blue).

3D anaglyph of flamingoes at London Zoo

My son was curious but not massively impressed.  So I decided to try and make it more exciting by showing him some 3D film clips from YouTube.  There is a NASA tour of the international space station (here) which he quite enjoyed and we talked about the astronaut and why he floated because there wasn't any gravity.  However the real favourite was a 3D rollercoaster clip which he thoroughly enjoyed and asked me to replay multiple times.  He experimented with taking the coloured filters off each eye and swapping them over, and we talked about how the screen is flat, but it looked and felt like he was on the rollercoaster with his 3D 'glasses'.  

Viewing 3D videos with red and blue filters

He's talked about rollercoasters since so I rather fear that he's gained an interest in riding rollercoasters (which I hate!) so this may not have been the wisest choice of activity on my part... maybe I'll stick to phonics with the filters next time!