Thaumatropes

28 January, 2010

The thaumatrope is a Victorian-era optical toy. It uses the perceptual effect of persistence of vision to merge two images on the alternate sides of a rapidly spinning disk.

This week, for our first Methods of Motion assignment, I constructed five thaumatropes. Two of these used the two most common thaumatrope illusions: superimposing one image on another and combining two disparate images into a new whole. In the other three, however, I experimented with a different approach: using a thaumatrope to combine both sides of a stereograph in order to create a 3D effect. This second experiment met with mixed, but intriguing, results.

Finally, I built a lego prototype for a thaumatrope viewer. Normally, thaumatropes are viewed by rotating bits of twine attached to each end of the disk, causing it to spin end-over-end. However, this makes it hard to regulate the speed of the spin and forces you to change directions every few seconds as the twine uncoils. This viewer would allow you to play the thaumatrope by turning a hand crank in one continuous and comfortable motion, making it easier to control the speed of the spin and possible to play the thaumatrope without interruption.

First, my conventional thaumatropes. Since the thaumatrope illusion is created by having part of the image be absent on one side of the disk, I thought it would be appropriate to depict absence in the imagery I used as well. The first thing that came to mind on that theme was the Dodo.

Dodo Bird thaumatrope:

This thaumatrope combines a photograph of a dodo bird skeleton in a museum case with an artist's rendering of what the dodo might have looked like. When combined, the painted dodo bird appears to have real photographed bones visible inside of it.

One technical lesson from this thaumatrope: to my surprise, the white background of the living bird blocked out the darker surroundings of the museum photo. I was imagining that the living bird would simply be superimposed on the photograph, but the white background altered the effect. If I had given the bird a black background, the superimposition might have worked better, allowing the light details from the museum scene to come through.

In my second attempt, World Trade Center thaumatrope, I used this effect of the white background to my advantage. Another obvious image that comes to mind on the theme of "absence" is the World Trade Center.

In this thaumatrope, I took two copies of the iconic photograph of the WTC towers from below and erased one tower from each copy, replacing it with a white geometric gap where the tower was removed. The effect when the images are combined is of ghostly flickering towers, as if the towers were both present and absent.

Now, the stereothaumatropes.

I started out with a stereographic print that I found on the web depicting women working in a stereograph factory:

I carefully separated both sides of this image and aligned them in Photoshop to create a two-frame animation that would create the 3D illusion by oscillating rapidly between the two, a "wigglegram":

Once I'd gotten the images lined up, I split them apart again and flipped one, working very carefully to ensure the alignment would stay consistent when I printed them out and assembled them (like all the other thaumatropes here, I had this one printed at Adorama photo in NYC, which I can't recommend highly enough; they give you 25 free prints for opening a new account and made really good quality prints from my uploaded digital files overnight). Stereograph Factory Stereothaumatrope:

The 3D effect is not as pronounced in the thaumatrope as the wigglegram above — largely because the thaumatrope is actually spinning so fast that the image blurs — but it is visible. And the effect is even stronger in person.

I produced two more stereothaumatropes in this same manner, one of the Old Faithful geiser:

(view Old Faithful Stereothaumatrope on YouTube)

and one of this rocky mountain:

(view Rocky Mountain Stereothaumatrope on YouTube)

In this last stereothaumatrope, as you can see, I experimented with an oval shape as it fit the image better and I hoped it would slow down the spinning to enhance the 3d illusion. This worked maybe too well, making this thaumatrope actually somewhat too difficult to operate.

Which brings me back to the idea of a thaumatrope player.

A design for such a player faces two main challenges. First, mounting the thaumatropes securely without altering them. An effective player would be able to operate on existing thaumatropes without spearing them with a shaft or creating any new holes in them. After some thinking, I realized this means needing to clamp onto them from the bottom and spin them around left-to-right rather than top-to-bottom.

The second challenge, then, is converting from the vertical motion that is natural for the human arm into a horizontal rotation to spin the thaumatrope. After some sketching, I came up with a mechanism that would use two 45 degree gears mounted orthogonally to transfer the rotation. Here's a video of a Lego prototype that demonstrates the idea:

Prototype lego thaumatrope player

The biggest problem with this design is that the thaumatrope only rotates once for each revolution you make with your hand. To make it possible to achieve faster rotation, the gear ratio between the crank and the thaumatrope should be higher: making the thaumatrope rotate more than once for every turn of the crank.

Unfortunately, the Lego kit is somewhat limited in its gear selection, but I was able to slightly increase the ratio in a later prototype:

Lego thaumatrope player with bigger gear

I intend to keep working on this thaumatrope player in my Mechanisms class with an eye towards eventually building it with real gears and lasercut parts.