I did a few experiments with bokeh a while back. Bokeh is japanese for "quality of blur". I suggest you first read the basics of bokeh here & then come back to this article where I will explain how you can play around with the shape of the bokeh.
I then shot a picture of my window's frame with the sun in the background.
This picture kicked off a whole lot of questions in my mind. Why is bokeh in that shape? how does it form and so on...
I then read up the "optics" chapter from my high school physics text book to recollect how lenses worked, what the various terms like focal length or focal plane meant and so on.
We all have heard that More the blades in the diaphragm, silkier & smoother the bokeh. So does the shape of the diaphragm have something to do with the bokeh?? YES IT DOES!
The first question I tried to answer was "If the shape of the diaphragm indirectly meant shape of bokeh then why not play around with the shape of the diaphragm". I know I cant build my own lens, so that rules out the possibility of my own diaphragm. the only option was to make a diaphragm & place it over my lens'.
So here's what I did:
Took a fast lens (you could use a slower one too - it works!) open it wide.With a sheet of black cloth, paper, chart etc cut an aperture thats narrower than the lens' widest. This way keeping the aperture sheet in front of the lens will result in the lens's aperture changing to the one I cut.
Make sure you cut different shapes. Good luck!