Article

3D Pulfrich Effect

This is one of many articles covering 3D subjects, most can be reached from with our 3D Section or from the article 3D Photography - An Introduction

3D created using the Pulfrich effect is of NO USE at all to still photographers, and has limited other applications. It has been used to demonstrate a form of 3D on TV, but is very limited.  We are only covering it really for completeness, although you may like to experiment with this.

The effect is obtained by tricking your brain. No nothing to do with politicians or statistics!!

So lets explain firstly how you produce it and then, explain why it works.

Something needs to move, it could be the subject, but its easier to see if you are moving. Look out of the right hand side of a car or train, and video the scene as it goes by, obviously not while you are driving. The best effect is obtained when you are travelling rather slowly, say 10MPH.

Now get a pair of sunglasses, flip down sunglasses, ordinary or Polaroid and remove the left lens so you have the sunglasses only over the right eye. Use this while watching your video, and you should see a 3D effect. It only works while you are moving and only in this direction.

So why does this work

Lets establish the facts involved:-

• things nearest to you move faster across the TV screen,

• the dark lens on the right eye reduces the intensity of the light received by the right eye,

• our brain takes longer to process dark scenes.

.It works because of the above, lets look at it in stages.

• By the time the brain has processed the fast moving tree in the right eye's scene, the left eye's tree has already moved further to the right.

• To focus the tree the eyes must cross more, thereby giving the illusion of a closer tree.

So, with the dark lens on the right eye, things that move faster to the right appear closer, and things that move faster to the left appear further away.

Use these special glasses to look out of the right of a car sitting behind the driver, and you will see super 3D. If you are outside the UK, its likely that the right side will be the opposite side to the driver, you will be in the same place only the driver has moved.

Another example

Lets give you another example - hang something on a piece of string from a point in the air, and swing it sideways. You can see it swings from side to side. Now put on the half sunglasses we used above and the item appears to swing in a circle. As it swings one way it appears to be forward and as it returns it appears to be further back, the fact that it slows towards the end of each swing makes it kook more circular.

Using this, you can spin something in a video, and get the same 3D effect, movement left to right appears to be in front of the part moving left to right.

When things stop, the 3D effect is lost completely, so its of no use at all for the still photographer, and for video production its of very limited use, difficult to script and direct, so perhaps its more of a novelty value.

See Also our 3D Section for more articles and projects on this topic.