Hey folks. I did a quick search and couldn't find anything, so I apologize if this has already been answered. I just bought a set of 3 extension tubes: 12mm, 20mm, and 36mm. The first thing I discovered to my dismay is that they will only work on my lensed that have manual f-stops (so my 18-70mm is out...). Anyway, here's my question. I threw them on my camera with my 50mm. I can get amazingly close, which is, of course, great and the point, but I notice that everything looks like those lensbabies...that is, the center is in focus but nothing else is. Is this normal? Is it because I'm using my 50mm (I also have a 70-300mm, which I haven't tried yet)? Am I doing something wrong? Also, can someone explain the numbers to me? Is it if I use the 12mm with my 50, it's like having a 62mm lens? That doesn't sound right...but I'm still not really getting the mm thing (I mean, I understand that with a 50mm lens, the light all comes to the point at 50mm from the lens to the sensor/film [and let's not get into digi/film conversion right now if we can avoid it]). Thanks.