Question

3. What is the relationship between aperture and shutter speed? How can you describe this relationship?

Answer 1

The aperture, ISO and shutter speed all must work in harmony to produce a correct exposure in any given light.

ISO, of course, is the measurement of the sensitivity to light of a light sensitive surface, either film or digital sensor.The lower the ISO (50, 100) the less sensitive and the more light required - and the better the picture since a low ISO produces minimal grain (film) or noise (digital).

The aperture (aka f-stop) is an opening formed by the movable blades of the diaphragm inside the lens. A large f-stop (f1.4, f2) admits all available light while a small f-stop (f8, f11, f16) admits very little light.

Shutter speed is based on the ISO and f-stop chosen and controls how long the light admitted by the lens is allowed to expose our film or sensor. The shutter speed also controls how motion is captured. Use a slow shutter speed and motion will be blurred (very effective with moving water or to add a sense of motion to a sports scene). Use a fast shutter speed and motion will be stopped or "frozen".

Answer 2

Also does some stuff to depth of field.

http://photography.about.com/od/takingpictures/ss/DOF_2.htm

So if you want a large depth of field, but have too slow a film/sensor, you can have problems.