Okay, I asked a few weeks ago regarding octaboxes. So, I figured I could try making one myself from a largish parasol I had lying around. I am in the middle of it right now. Materials are bought, the skeleton assembled in a new apex (for fitting my portable flash) etc. So I started thinking about the shape of the reflective fabric sections. Turns out it was more difficult than I had planned. Octagonal paraboloids, or polygonal paraboiloids in general isn't really a matter that should be taken lightly. But there are a few solar cooking enthusiast who have written a fair amount on the subject. The problem is that their calculations are more focused around focal points, then even light. The biggest problem was that you always have the arc length given in an umbrella based octabox, soft box, and that you are more interested in base area or depth of the thing. So I sat around and made a small octave/matlab script. It isn't really optimal in any sense, and it doesn't yield the nice straight end edges you see in commercial products. But hey, if it helps anyone, I'm happy. Use it as you please. It renders a few data files which can be plotted with gnuplot. Both gnuplot and octave are open source and quite nice if you are used to terminal work. You need the arc_length function for the octabox script to work. Rename them to just *.m to get them to work in matlab or octave. I couldn't attach them, but if you find yourself lusting for building an polygon softbox, pm me. EDIT: Oh I could!