Is it possible to create a metal ring with a variable diameter using segments?

[examorph]

I am interested to see if there is a way of creating a metal ring which has a variable diameter, the only way I imagine that this can be done is using segments which come together to form a circle, once pulled away the diameter changes however, the problem I face is that when the segments are pulled out, they leave a gap as shown here:
http://gyazo.com/bd38ce382a16a9f6a1739c42ad30d404
To fill this gap, additional segments would need to be manufactured and would defeat the purpose of having a variable diameter.

Is something like this even possible, if not a perfect circle, is there a way of doing this to get a varying geometry which is very similar to a circle? I am interested to see any ideas at all that anyone may have about this even if they are nothing to do with segment please share.

 

[phinds]

google "camera iris"

 

[examorph]

That was exactly what I was looking for, Thank you.

Just out of interest, can this be reversed? I mean rather than having a circle form on the inside is it possible to form the circle on the outside so that as the segments move it expands outwards?

 

[phinds]

That was exactly what I was looking for, Thank you.

Just out of interest, can this be reversed? I mean rather than having a circle form on the inside is it possible to form the circle on the outside so that as the segments move it expands outwards?

Never heard of one like that but seems to me it could be made. The "circle" would probably be more like a polygon, but the more segments used the less that would be the case.

 

[Baluncore]

There are many unusual approximate solutions to such a problem.
Maybe if you could identify the application it would be worth posting other solutions.