All you need is
1. 2 20"X30" Sheets of White Foam Core Posterboard - ($2 a sheet)
2. 3 11"X17" Sheets of Vellum Paper ($11 for 50 sheet pad)
3. White Duct Tape ($2 a roll)
4. 3 Clamp Lamps ($5 each)
5. Clear Scotch Tape (you probably already have some lying around)
*prices may vary depending on where you shop*
Cut the first sheet of foamcore into 1 15"X20" piece (for the back wall) and one 13"X20" piece (for the top diffuser) Trim what's left into a 15"X2" strip to be used later as a "spacer" to make the whole thing tri-foldable.
Cut the second piece of foamcore into 2 15"X13" pieces (for the side diffusers).
Cut a centered 10"X12" square hole in each of the side diffusers and a centered 10"X16" square hole in the top diffuser.
(template coming as soon as I can draw one off)
Lay the back wall and one side piece down flat with their 15" sides touching. Tape them together using the white duct tape along the full length of the joined edges. Fold the side piece inward book-style and run a second piece of duct tape along the outside of the fold, much like the spine of a book.

Before attaching the opposite side diffuser, attach the 15"X2" strip flat atop and along the edge of the back wall. This spacer will ultimately allow the second side diffuser to fold inward and flat ontop of the first side diffuser without tearing away from the back wall.

Use your spare bit of foamcore to lay under the right side diffuser so that its 15" edge lays flush against the right edge of the spacer strip attached to the back wall. Tape the edges together just like with the left side, and then fold it in and tape the outside of the fold bookbinder style.
When fitting the paper, you will need to trim away some of its length to fit the side diffusers, but the top should be a perfect fit with 1/2" of paper overlapping all around the cutout. I placed a few patches of the white tape on the corners and sides of the cutout so that if the vellum gets torn and needs to be replaced, the clear Scotch tape that is used to secure it in place can be pulled away without ripping the paper outer-layer of the foamcore.
The clamp-lamps are lightweight and cheap, and the reflectors can be removed and nested for compact storage or transport.
Once finished, the whole thing stands 15" tall and can handle most models, including dragons and some smaller scenery.

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Note on my version, the paper isn't quite big enough to fill the holes. I did not think I would find any vellum paper locally so I sized mine for baking parchment. Parchment does okay, but the vellum delivers a whiter and more even light.
The clamp-lamps for the side diffusers can be laid directly on the tabletop if there is nothing readily available to clamp them to. (Lucky for me I have a few drawers and cabinets handy). I am working on a cheap portable solution for placing the top lamp though. I am thinking the simple wooden-based upright-spindle paper-towel holder might be the best bet.
Also, I am planning on adding a thin magnetic strip across the back wall for a quick and easy way to attach and remove printed backdrop images, but only if the strip does not interfere with the foldability of the lightbox.
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Here's my first subject... Yagun Oooooooooooooooooooooooooooooog!


