This is something I've been meaning to try for ages. I love the way the camera iris works, a small turn of the iris ring and the central hole expands or contacts. 

Camera irises have varying numbers of vanes, the more vanes, the closer the resulting hole is to a circle. In this prototype I've used five vanes, a reasonable balance between a nicely circular hole and having loads of fiddly bits to cut out. 

Next step is to make a slightly larger prototype where the hole is larger in relation to the surrounding rim. I might also try different numbers of vanes just out of interest. 

I'd like to add the iris to the top of a gift box to make an interesting closeable container. Do you have any other ideas how it could be used? Leave a comment!