How To Make A Cone Softbox For Your Speedlight
If you are doing portraiture with speedlight, you know that to get soft flattering light, you need to increase the size of the light source. We have featured a few hot shoe softboxes before. In fact the first ever post on DIYP was a small hot shoe strobe's softbox tutorial. And we also had a poorman's octabank. But this is the first time we are sharing a cone shaped one by Peter Beckerman. (Sewing skills for the win!)
A while back I was trolling through the pages at DIYPhotography.net (great site BTW) when I came upon this post, which describes the construction of small diffusers for your speedlight. As that was something I was interested in, I downloaded the template, and fired up the old Singer (actually it's a Kenmore) and had a go. After much gluing and sewing I had the basic framework of the thing (I only needed to attach the front diffuser) and I realized that it wouldn’t fit on any of my speedlights, the smaller hole was TOO small! I don’t know if it was designed to fit a smaller light, or if the template got shrunk on my end, or if my sewing skills just suck (well I know my sewing skills suck) but whatever the reason I had wasted quite a lot of time patching the thing together and all I had to show for it was a black cloth lampshade!
There had to be a better way, that involved less sewing skills, was the right size (or could be made in different sizes) and still looked reasonable.
A Cone, a Cone! That’s the way to get the shape, without so much sewing machine action. Furthermore, a few changes in the calculations and I could make one in any size I liked (or at least any size I could manage).
So first I needed to make sure I didn’t have a repeat of my first small softbox fiasco. I started by measuring my speedlights. After pulling out all of my flashes I determined that a three inch hole should flatten down and fit on any of my flashes (you’ll need to be able to get your hand inside the diffuser, for reasons which will become apparent as we go, so if you're using three inches, test and make sure your hand will fit through the opening).
For the business end I first tried 12”, which is nice, but if I want to keep the flash on the camera, it’s a bit too big. 8” works better for that, and using no science or logic whatsoever I decided that about 8” tall would be about right. The Key Materials I used are a cheap car window sunshade, some glow bracelets, Velcro, and some white and black cloth.
Making A Cone Template
So next I needed some calculations from which I could create a template. A quick Google search for “cone calculator” yielded several excellent examples of which I liked this one best.
After plugging the numbers into the calculator we get a radius for the small hole as 5.028916”, close enough to 5 for my purpose, and 13.41044” for the large circle which I converted to 13 7/16” as close enough. The all important pattern angle comes in at: 107.3789 degrees, 107 is close enough for me. So to make my template I first needed a piece of paper to draw onto. The back side of some holiday wrapping paper, or even some old newspaper will work in a pinch. I had some paper sheets that had been used for padding in a box, and that worked nicely. The paper needs to be at least twice the large hole radius, or about 27 inches long. First near the edge I drew a straight line about 27 inches long.
Then I found the center, and using a compass I drew a half circle that reached 5 inches to each side of the center point (this will be the small hole).
Next, because my compass was too small, using a loop of string, I drew a larger half circle that reached 13 7/16 inches on each side of the center point.
If you have one of those little “string locks” that you find on jackets, backpacks and lots of camping gear, it makes it easier to fine tune the measurement of the circle, however in the future I think I’ll just use a small piece of scrap wood, with a small nail for a point and a carefully placed hole just big enough to let the point of a pencil poke through, I think that would be faster and more accurate.
Now that we have the two circles, we need to measure the pattern angle. Take a protractor, like you used in grade school, and line it up with the straight line at the center point. Make a mark at 107 degrees, and draw a straight line which starts at the center point and runs through the 107 degree mark continuing to the larger half circle. This is the basic cone pattern.
Lastly we need to extend the pattern along the arc of the circle for one inch from the 107 degree line to create a ½ inch seam allowance.
Now cut along this line from one circle arch to the other, then along the edges of both circles, and the straight line that connects the arcs.
Congratulations! You’ve made your template. Now to turn it into a diffuser.
For the reflective inside of the diffuser I cut up a cheap automotive windshield sun screen which I got at a local dollar store. It’s basically a reflective Mylar blanket glued to foam backing.
I like it because the Mylar is very reflective and the foam is light weight and helps the diffuser hold its shape a bit. Around the edge of the sun screen is a black fabric edging. Using a seam ripper or just a razor blade I cut the stitching and saved the edging material for later use (waste not, want not).
Next I pinned the template to the sunscreen.....
....and cut a piece of the screen to the shape of the template.
Piecing it together
Using some adhesive spray I applied a coating of adhesive to the back (foam side) of the sunscreen, and another to a piece of black cloth, after a minute I joined the two together, making sure to eliminate any gaps between the two and let dry for a bit.
Next I cut off the excess cloth, so that I had the Mylar on one side and the black cloth on the other. (If you are unable the find one of these Mylar sunshields, you might try using the spray adhesive to glue a piece of heavy duty aluminum foil to a piece of black cloth. Then pin the template, and cut to shape.)
At this point the (reflective) inside should look like this
The black cloth outside should look like this
Sewing it all together
Cut a bit of the black edging material that we saved, and use it to trim the smaller arc. Just fold it over the edge and sew into place.
Next, with the shiny side out, bend so that the two straight edges meet. Line them up as best you can and sew parallel to the straight edge ½ inch in from the edge.
Next trim the excess (I leave between 1/8 and ¼ inch).
I like to cover the edge of the large circle now, as the edging runs across the seam, and I think it should look better, but you could do the big edge at the same time you do the smaller arc. Just use some more of the saved edging, fold it over the end of the cone, pin it, and sew into place.
Here come the glow bracelets!
Before we go any further, we need to work with the Glow Bracelets. You can probably pick these up at the dollar store when you get the Mylar sunshield. My local store has them for 5 for a dollar (I've seen them for 15 for a buck). I use about three for an 8 inch diffuser. You’ll need something you can cut these with.
I use a small pair of wire cutters. A word of caution: The chemicals inside one of these glow sticks is not toxic, however the two chemicals are kept separate by a very thin walled glass tube into which one of the chemicals is placed.
When you want to use the glow stick as intended, you bend the plastic tube and thereby break the glass tube allowing the chemicals to mix. It’s REALLY easy to break the glass tube, and lots of tiny sharp shards of glass can result, so use caution when cutting these tubes open, and take care when disposing of the glass, so that someone down the line doesn’t get slashed. Also, when the two chemicals mix the result, while non-toxic, doesn’t smell very good, so some ventilation may be in order. I don’t know if these chemicals can stain skin or clothing, so I use gloves etc.
I cut these as close to the ends as possible.
Once the second end is clipped the glass tube slides right out. Then just rinse the resulting plastic tube in water to clean them out and let them air dry.
Using the supplied couplers I can join as many of these tubes together as I need for whatever size of diffuser I’m making.
For the 8 inch diffuser I use three, but I don’t push them all the way into the coupler, instead I leave the ends as far apart as possible, and it seems to work just fine.
Bringing it all together
The plastic hoop is now used to help the diffuser body hold its cone shape while the cloth front is sewn on. Just slide the hoop onto the body until it fits snug, without forcing it. A few bits of tape (nothing too tacky as the Mylar will peel off when you remove the tape later) helps to hold the hoop in place.
The front diffuser cloth is the trickiest part. Ideally it will be sewn with equal amounts of tension all the way round and be very slightly taught after final assembly.
Frankly I’ve never gotten close to that. I’ve made numerous attempts at getting this part right, and my best results have been achieved by making a few marks around the circumference, and using those as a guide while I pin the front in place, then I hand sew the front on. If anyone can come up with a better way to do this part, please let me know.
I’ve tried making numerous marks (like every ¼ inch) and just doing about 8 total, and both work about the same. Just try to get it centered then pin it so that it is as evenly taught as possible. Then hand sew (NOW you know why you need to able to get your hand into the small end)!
When the sewing is complete, the plastic hoop is removed, and the excess cloth trimmed.
Some Velcro strips at the small end to hold it to your speedlight.
Lastly it has to be carefully turned inside-out, and VIOLA, you’ve just made a flash mounted soft box!
Now take that plastic hoop and push it INSIDE through the small hole and line it up around the edge of the big end of the cone. This’ll help the soft box hold its shape. When you want to pack up, just pull the hoop out, pull the tubes apart (don’t lose the couplers) and fold up the fabric part.