ENGINEERING: How does the spiral opening wheel/cirlce (like in james bond) work??

Question

Here's a picture of what I'm taking about: http://i34.photobucket.com/albums/d119/spyyder/spiralwheel.jpg

On the pic, the 2 small pictures on the left is the Itunes 'burning' icon that shows an animation of what I'm looking for, and the bigger right picture is it again with marked arrows. Whats the thing called? How does it work (how do the fins move)?

Thanks for any help!

Answer 1

It's called an "iris" and is used in spot lights and the like.

What you are looking at in the picture is a load of individual plates (the curved radial lines are their edges) with one end at the opening and the other anchored on a pivot at the edge of the mechanism.

Every single one is operated at exactly the same time, and is done so by changing the angle about the pivot (at the edge). As the angle of the plate gets closer to the radius, the opening in the middle gets smaller, and as the angle of the plate gets closer to the circumfrence/edge, the opening gets larger.

The more plates there are, the more perfect the circle opening is.

Thinking about it, the one on James Bond is probably not one of these at all, but the inside of the gun as the bullet is fired (i.e. the camera is mounted on the front of the bullet). The inside of the gun barrel is made with spirals in it to encourage the bullet to spin as it leaves the barrel (making the shot more accurate).