When parallel rays of light strike a lens focused at infinity, they converge to a point called the focal point. The focal length of the lens is then defined as the distance from the middle of the lens to its focal point.
This video shows you in simple steps how to do close-up using Micro-Nikkor and third-party close-up lenses and how to do 1:1 magnification. Remember, this tutorial is for controlled situations (which means we won't show you how to do bugs, portraits, or pets at 1:1 magnification). Enjoy!