OK here's a step by step. Obviously you can fill in some of the little gaps with common sense but i'll cover the main points.
1) You'll need 5 toilet rolls. cut a slit down 2 of them to open them out. don't force them open.
2) grap a marker pen, your camera/lens and the toilet rolls and fit them around the lens. make a mark to show where you're going to join the two toilet rolls. leave a couple of mm slack as you'll take this up later.
3) tape the two toilet rolls together. you should now have a tube that your lens fits into. You want to cover this in tin foil. i used PVA glue spread thinly.
4) Now to make the diffuser. decide how wide you want the ring of light to be. mine is 2cm. At this point you might want to dig out your old compass so you can get your circles right. draw around the inside of the tube you made (it dosen't have to be a perfect circle). Draw it on a peice of white A4. now get out your compass and draw a circle around it thats 2cm bigger. This'll be your template for cutting out the peice of plastic milk bottle that is going to become your diffuser. All you have to do is cut out a flat (ish) piece of milk bottle and if its not flat like mine was stick a teatowel over it and iron it out. You might have something better than milk bottle lying around that you can use but this worked OK for me.
5) Next lay your plastic over the template you just drew and mark it off with permanent pen. You want to leave tabs on the inside and outside of the ring so you can fix it into your tube structure. It should look kind of like a cog. cut it out and fold the tabs (i scored them first so i could bend the plastic). Hopefully you can see where this is going.
6) make the outer tube by using the template you drew to stick your remaining 3 toilet rolls together in the right size using sellotape.
7) coat the inside of the tube with tin foil (PVA time again)
8) Now you can assemble the two tubes and the plastic diffuser ring. Use the tabs to sellotape the diffuser to the insides of the tube structure. Mine didn't quite fit so some of the tabs were between the two layers of the tube and some were inside the middle tube, which is why i said to leave a couple of mm between your inner tube and the lens diameter.
9) i made a stopper at the back out of card coated in foil just to stop light escaping out the back
10) Now you can make the bridge or the tunnel which will fit over your on-board flash and deflect the light into the tunnel. Once the glue has dried fit the whole thing over your lens and work out how long you need your bridge structure to be. I made mine so that it fit all the way over and came down around the back of the flash so that any light going backwards was deflected towards the front. Just make the whole thing out of one piece of sturdy card, cereal box would probably work. score the bits you need to fold, cover the inside with foil.
11) You can see where i've attached mine to the ring structure, all i did was cut two slits and bent the flap upwards and used this to attach to my bridge. I left it free to move up and down which makes it easier to fit.
12) That it, finished. go out and test your new ringflash!
Any questions?
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