Depends on type/brand..what lens are you using? i have a Grobartig 0.45x wide angle converter .It's worth having when you're shooting wider perspectives.Adding at least .45% of youre lens view.Of course it's not that wide enough to cover the maximum aperture of your lens coz vignetting will occur (a dark edging occurence on corners as you pull back your lens to it's maximum widest aperture)
But at least it adds extra view to your current lens.
I have it for sale..follow this link:http://forums.clubsnap.org/newreply.php?do=newreply&p=3112797
