It’s common knowledge that the bokeh in pictures will reveal what the aperture looks like. A good example are lights turning into stars when you do long exposure with small amerture, like f16.
For this trick you will need a lens with big aperture, like f1.8 or f1.4, otherwise your custom aperture and the internal aperture will overlap (or you need to make yours really small). I used an old Nikkor f1.4 manual focus lens.
With this, I created the following cheesy shots:
This way you can create nice backgrounds for your christmas shots. 🙂