I think I'm going to purchase a d50 this xmas and and trying to figure out what lens (likely 2) to get with the body. Nikon offers a bundle w/ the d50 and a 18-55 lens.

If I'm not mistaken, these number (18-70 and 18-55) refer to the min/max focal length of the lens which directly impacts the zoom of the lens. If the fspot ratings on the two are the same, what does the extra 15 mm give you? Is it zoom or is it perspective or both?

Finally, how can I translate these numbers to "power"? In other words, how far can I zoom with a 18-55 lens in terms of x (several websites claim this is a 3x lens). How can I calculate this for other ranges like 18-70 and the 55-200 am I also considering.

Thanks guys!