I just want to know how much magnification there is... if I have a point and shoot camera and it has 10X zoom, I'm seeing that the subject is "brought" 10x closer. So, what does a dSLR telephoto lens need to be to bring the subject 10X closer? I am looking to buy a 55-200mm Sony lens - will the subject be approximately 10x closer? Or 5x closer or 15x closer?
To answer your question we need to know two things:
- The max focal length of the lens (200?)
- The "normal focal length" for your sensor size (about 45mm on a FF DSLR), but much smaller on a P&S
Now just divide number #1 by #2, so on my FF DSLR a ~200mm lens makes things look 4x closer. The 10x zoom advertising copy on P&S cameras has to do with how large a range the lens covers, which of course has a relationship to how close it can make things look, but by itself cannot answer your question.