As a devout reader of David Hobby's wonderful blog "Strobist" I have a great debt to pay to the online photo community for teaching me much of what I know about photography and in particular... lighting. This is my humble attempt at giving something back.
So this buddy of mine has a really cool 26" softbox (Wescott Apollo) that is unique in that it has an internal umbrella shaft and can be used with an ordinary lightstand and speedlight, without any additional hardware. So these softboxes are great, except they cost $140 USD so I set out to make something similar for $23 and it works like a champ! I also wanted something that looked at least sort-of professional, was collapsable and fully portable.
What you will need:
1 45" Westcott silvered on the inside, black on the outside umbrella (needs 8 internal ribs and MUST be a single fold design, ie. NOT a compact umbrella)
4" of 16ga wire
1yd translucent fabric
needle or sewing machine
These two photos show the starting umbrella and what the inside will look like with a strobe in place
Step 1: Remove the fabric from the frame
So your umbrella needs to have 8 "legs", and you need to carefully cut the threads on EVERY OTHER leg, that hold it to the fabric. The goal is to then pivot the 4 (now) free-floating legs to be paired with each of the adjacent 4 still attached legs.
After you cut the outer threads attached to the tips of the metal supports, you will need to re-glue the tips back on to prevent them from poking through the outer fabric.
Step 2: Tape the free floating legs to the still attached ones
Just use a couple inches of gaffers tape for this.
Now you should have an umbrella with four doubled legs
Step 3: Mark and cut the internal braces
The reason for this step is that you need to shorten the internal bracing, in order to re-use the original locking mechanism that holds the umbrella open. Recall that we are going to be using this in a 3/4 open position, compared to the original umbrella, and we need to adjust the internal bracing length. This is probably the hardest step in the whole process (in particular the drilling of the new holes).
Position the center slider about 5 inches below the position where it normally rests, tape it in place. Now use thread or string to tie the opposite corners together, while slightly bowing the umbrella legs. We will need to shorten the internal braces, so measure the length that they will have to be cut to. On this umbrella for a 28" x 28" softbox, my leg braces needed to be about 10-10.5 inches.
Now cut the wire that holds the internal braces to the center slider.
Shorten the internal braces by cutting them with a wire cutter, flattening the ends with pliers, then re-drilling the tiny hole in the tips (to replicate the original hole).
Step 4: Reattach the center supports with wire
Re-thread the center supports with wire, twist with pliers to finish.
Step 5: Gather additional fabric in the umbrella shell
Now re-attach the string/threads that hold the softbox in a square shape and the proper dimensions. Here I would encourage you to tie it slightly undersize (because there is a lot of stretch in the seam and fabric. So for a 28" finished softbox, tie it in a 26" x 26" square.
Now gather the extra fabric between the 4 legs. Three of them will need to have this extra flap sewn shut (leaving the gather on the inside). This pretty much requires some hand sewing, because its impossible to get a sewing machine inside the umbrella. If you want an easier time sewing, this can easily be done if you decide you don't mind having the gathers/seams on the outside of the finished softbox.
Only sew 3 or the 4 gathers. The 4th is where the lightstand will go, so you need to cut and hem about a 12" slit in one side.
Also measure about 4" in from the 4 points of the umbrella where the ribs where removed, and trim off this extra "point" of fabric, making a clean square profile to the lip of the box.
Step 6: Cut the shaft down
Now the center shaft needs to be carefully cut down, so as not to protrude through the center of the face of the softbox. My center shaft was aluminium and if you have a pipe cutter, use it! I didn't so I used wire cutters to slowly crimp/cut the shaft while rotating it. This produced a fairly smooth, non-jagged end of the shaft. It took about 30-40 gentle crimps with the wire cutters, evenly distributed around the circumfrence of the shaft.
Step 7: Sew the edges of the flap shut
Use a strip of the leftover exterior fabric to splice the ends of the access flaps together. Make sure you make that edge dimension 28" overall when you do it.
Step 8: Cut and attach the face fabric
I bought some fabric at Joann for $2.99/yd and cut a 29"x29" square out of it. Use pins or staples to attach it to the edge of the softbox temporarily.
Now go back and sew the whole thing together around the perimeter.
Step 9: Done!
This finished softbox works best with the speedlight pointed into the back of it (produces most even illumination). If you stop down to a really low aperture, you can see the shadow of the lightstand/speedlight in the face of the softbox, but this is pretty minor.
Additionally you can point the head of your speedlight UP towards to top of the softbox to create assymetrical lighting similar to what you would get out of a striplight.
Another variation is that you do not have to make this thing square either, if you want a rectangular softbox, you can easily modify these plans to do so.
In the end you have a collapsable softbox, that uses te original locking mechanism to hold it open, that is compatible with speedlights, and mounts on a standard lightstand. Total cost $23.