Shape of Bokeh

This is a quick note and just wanted to write it down before I forget. Today I was reading 'Understanding Exposure: How to Shoot Great Photographs with a Film or Digital Camera' by Bryan Peterson, recommended by Spencer Fu at a forum I always go to RFD! and I realized something which is kind of obvious but never really thought about it. I never realized that, I could control how my bokeh looks like.

The book explained that if I wanted a circular bokeh, I would shoot wide open, cause the aperture basically does not constrict the light and the bokeh just mimics the shape of the lens barrel. If I wanted a hexagonal shaped bokeh, I would just need to step the aperture down. Reason being, the aperture when constricted is not perfectly circular, but more of a hexagonal shape. When I read this it was one of those WOW moments, no matter how obvious/simple that realization was, I now know a simple trick that is subtle but could make a big difference in a future photo.