Parabolic Reflector Calculator For Softboxes
Does all the long-winded, repetitive trigonometry... So you don't have to!
Diameter of softbox: cm
Depth of softbox (recommended: 47cm): cm
Number of sections (recommended: 8 to 12):
Explanation of use
All measurements are in metric. It's much easier to do this kind of trigonometric manipulation, measurement and building in a base 10 system. Also, it's the 21st century. ;)
The diameter is across the widest point of the reflector at the front, between opposite parallel sides of the square or octagon. The depth is front to back at the centre. I say 47cm is recommended because that's what the Profoto softboxes all are. You don't have to use this value if you don't want to.
The number of sections dictates the smoothness of the curve. The more sections you have, the closer it will be to a true parabola, but it will also increase the amount of effort involved significantly without, I suspect, any kind of significant improvement in light quality. I think that around ten sections is probably sufficient. Alternatively, you could make it easy and just use two or three sections. It's entirely up to you; feel free to experiment.
Interpreting the results
The first column is the lengths between the current row's point and the previous point, that I've termed "dl." These are the actual lengths of the sections when laid out flat, as seen below.
The second columns, w, are the total width of each section. Draw a line this length perpendicular to dl, centered on the x-axis.
© 2012 Rob Taylor. Permission hereby granted for free personal and commercial use, saving for offline use, alteration and redistribution, with appropriate attribution given. Please do not redistribute this page or tool commercially or bundle for sale.