i've been on the look out for a good candidate in the shops for ages, everything the right size is usually too clear but i spotted this.
it's pretty wide so it covers the flash nicely but i made the hole for the lens slightly too big so it needs to be stuck on with blu-tac. it's not a perfect light spread as there's a bit of left/right light/dark but it's alot better than without i think. i left the lid on and cut a hole in that too.
pic about half-size, i just dropped the screw inside then put the lens through the hole and shot, it's like a mini light tent almost

this guy is still hanging around on the corner of a door frame in my kitchen, it's been there nearly 24 hours now, shots before of it were at f/2.8 but with the ringflash i could put it in AV mode and use f/8 then experiment with the 12 flash settings, could only find 3 settings in manual mode for flash, dull-too bright-nuke, unless i'm missing something.
i'm still on the look-out for better pots to use maybe something a bit thicker will diffuse better?