Focal Length

Focal lenth is the distance from the lens to the image sensor (or film), when focused on something closer than infinity, the lens is moved farther away from the image sensor. This is why most lenses get longer when you zoom In.

In 35mm photography, lenses with a focal length of 50mm are called "normal" because they work without reduction or magnification and create images the way we see the scene with our naked eyes. Focal length less than 20mm are called "Super Wide Angle", 24mm - 35m are called "Wide Angle", 80mm - 300mm are called "Tele" and beyond 300mm are called "Super Tele".

Attached eight photos were taken from the same place with Panasonic DMC-FZ8 digital camera by using different focal length from 36mm to 648mm, the 8th photo is taken with 4x digital zoom. (Digital zoom is not really zoom in the strictest definition of the term. What digital zoom does is enlarge a portion of the image, thus 'simulating' optical zoom. In other words, the camera crops a portion of the image and then enlarges it back to size. In so doing, you lose image quality.)