not being able to focus when you get too close is exactly what i am avoiding here... this allows extremely close focus.
i think what you have is a wide angle adapter but they might also market it as a macro attachment, but if it is what i think it is its a real cheapy way to go and the glass in it probably isnt very good.
what i am using in particular is for nikon and the part number is br2a... its not the greatest thing ever but its cheap and fun for anyone interested. you can find it at any pro camera store or at
www.bhphotovideo.com