Lenses

Focal Length

The Primary attribute of a photographic lens is the Focal Length. This can range from 4mm to 200mm+. There are a two aspects of the resulting shot that are affected by the Focal length:

Focal Length Categories

Cameras Within certain ranges of Focal lengths are classified into categories:

Fish Eye - 4mm - 14mm

These are extreme wide lenses that produce distorted images.

Wide Angle - 14mm - 35mm

These Lengths still add some distortion to your shot. They can be used to include scenery and location along with your subject.

Standard - 35mm - 85mm

These Lengths feel similar to the human eye and thus give a very natural look to your shots.

Telephoto- 85mm+

These Focal Lengths give a very narrow angle of view with high magnification. This allows you to capture a subject that is farther away, but can also give a unique effect in the way it compresses the space making objects in your shot appear much closer to eachother than they actually are.

Prime Vs. Zoom Lenses

Lenses can be Fixed Focal Length (Prime) Or Variable Focal Length (Zoom). So while a 50mm prime lens is fixed at 50mm, a zoom lens has a range of focal lengths that can be adjusted as needed.

And Here is a Great Article about Aperture, Shutter and ISO and how they relate to one another as it pertains to aperture.