Can someone ell me how slave flash units work? Do I need only specific ones for the K100D? What do I look for? I have an older pentax external hotshow flash, but I think it could have burned out my l;astcamera so I am not using it. I would like something to use that doesn't need to be attached to my camera while waiting for for new flash in August. Can a slave be used without ever touching my camera? Thanks!