We have another Photo Premium tutorial exclusively available to Premium members today. In this tutorial, we’ll teach you how to make a real softbox. Learn more after the jump!
Professional softboxes cost hundreds of dollars, and the cheap eBay ones are a risky investment in terms of quality. The DIY route may seem daunting, but this guide should make designing and building your own custom softbox feel within your grasp. Well, that is if you're not afraid of a little math!
With the scope of this article, I'm assuming you know what a softbox is and why you need it (unless you're a magical unicorn of light like Joe McNally).
We've all seen the before-and-after photos illustrating why you need a softbox, and now you want to take that next step. But putting up the kind of cash they seem to demand is either impossible, daunting, or outright offensive to you. So what do you do? You build your own, of course!
I'm going to cover a variety of shapes and sizes of reflector, as each requires a slightly different method for designing and some have particular concerns or uses to be aware of.
In this theoretical primer, by the end you should understand the factors which contribute to the quality of the light from a softbox, how the light moves through the softbox, and how to set about designing your own to build.
I'm going to keep the mathematics as basic as possible, and accompany it with as many diagrams as possible to help keep it relatable to physical phenomena, but if you can roughly remember your high school geometry lesson, you should find it reasonably straightforward.
The first type of softbox I'm going to look at is the usual kind that people tend to make themselves, the flat-sided, pyramidal shape. There's even a tutorial on this very site to help you with the build here.
These are very easy to construct and require very little math to design. The downside of this ease of construction is the fact that the light quality they produce isn't as high as from a parabolic reflector. This is due to the fact that the sides are the same angle all the way up, but of course the light is from a single point (the strobe head) so it's not hitting all of the wall at the same angle and being bounced out straight at the subject.
It's more spread out, similar to a strobe head itself (Fig. 1). Good diffusion material at the front will help alleviate this issue a little though. However, if all you're looking for is a simple build in the size and shape that you want as a start to your foray into light modification, this type should do the trick.
Fig. 1: The spherical output of flat-sided softbox.
The Simplicity of Pyramids
For pyramidal construction based on a regular polygon being symmetrical, with all equal sides, all you need is a set of identical isosceles triangles which attach together at the equal sides. To create these triangles you need just two measurements, based on your desired dimensions.
Using some basic trigonometry, we can convert these three-dimensional product dimensions (Fig. 2) into two-dimensional net dimensions to cut out (Fig. 3). Different numbers of sides require slightly different equations, so here they are for four-, six-, and eight-sided reflectors. Once you see how it works, you can do different numbers of sides with ease.
Fig. 2: Dimensions of a regular polygonal softbox.
Fig. 3: Dimensions of the 2D surfaces.
Fig. 4 shows the two right-angle triangles within a pyramid which we can use some basic trigonometry on to calculate the l and w values we need.
You'll note that in the case of square pyramids, softbox diameter d and triangle width w are equal, so we don't need to use the red triangle in this instance. We do, however, need triangle length l because of course, it's not the same as softbox depth z. To find l based on z and d, we can refer to good old Pythagorean Theorem: a2 + b2 = c2.
Fig. 4: Right-angle triangles within a square pyramid.
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