Thanks for the link Andy.
Saw the prices in $$ and nearly fell off my chair.
I will read through the linked pages at my leisure.
I will mod my Metz 45 first with a Cokin IR filter, and then the Vivitar 283 and Nikon SB80-DX with film filters all for a lot less than that.
As far as power loss goes you are right, but then multiple flash exposures on a single frame is a cost free way round that problem as I will only be doing still life.
Don