Lens hood for 18mm full frame lens

I'm eyeing up an 18 - 28mm lens for my K-1. It's just a cheapie to test out if I have much use for such a lens. One thing is bothering me a little so I come to the cognoscenti for advice. At 18mm I'm thinking lens hood and whether it's practical at all, especially as the filter thread is 72mm. Any tips or tricks?

Most of these lenses had a dedicated hood to match the lens at its widest - at 18mm is it a Fisheye or is it rectilinear? If it's corrected (rectilinear) then a hood designated ultra-wide may well do the job, but without trying it you won't be certain as to whether it vignettes or not. Sorry this doesn't actually answer your question but a search on Ebay for a cheap 72mm ultra-wide hood will probably be your easiest way of finding out (unless you can identify the original hood and search for that)!