CAMERA BASICS

Aperture (Av): (def.) - Hole/opening that varies in size (depending on how much light it is required to be let through).  It is controlled by a mechanism called the "Iris Diaphragm", which allows more control than in the past.  F. Stop is the term used to describe the size of the hole.

Smaller aperture sizes such as f/22 let in less light and allow for a greater depth of field (more of the shot will be in focus), whereas a larger aperture size such as f/1.4 will let in MORE light but will have a much shorter depth of field.

ON MY CAMERA (Canon EOS 400D), these are the Aperture Sizes available with the Kit Lens (smallest to largest hole):

f/29< f/25< f/22< f/20< f/18< f/16< f/14< f/13< f/11< f/10< f/9< f/8< f/7.1< f/6.3< f/5.6< f/5< f/4.5< f/4.0


Shutter (Tv): (def.) - Mechanism that begins and ends the exposure.  Different speeds let in different amounts of light and are usually expressed in seconds or fractions of a second.  
There are 2 different kinds of shutters: Focal Plane Shutters, which operate directly in-front of the film/sensor, and BTL (leaf) shutters, which operate inside the lens much like a diaphragm.

ON MY CAMERA the shutter speed times are as follows:

30"> 25"> 20"> 15"> 13"> 10"> 8"> 6"> 5"> 4"> 3.2"> 2"5> 2"> 1"6> 1"3> 1"> 0"8> 0"6> 0"5> 0"4> 0"3> 1/4> 1/5> 1/6> 1/8> 1/10> 1/13> 1/15> 1/20> 1/25> 1/30> 1/40> 1/50> 1/60> 1/80> 1/100> 1/125> 1/160> 1/200> 1/250> 1/320> 1/400> 1/500> 1/640> 1/800> 1/1000> 1/1250> 1/1600> 1/2000> 1/2500> 1/3200> 1/4000>

Exposure: (def.) - Total amount of light captured:

                Exp. = Time (shutter speed) x Intensity (aperture size)
                   = Tv x Av