What you're talking about is "field of view", also sometimes referred to (incorrectly) as "zoom factor". It's a direct function of the focal length of the lens used: the longer the focal length (usually expressed in millimeters), the tighter the field of view will be, and the closer the objects will appear.
For a complex, technical explanation, check here:
http://en.wikipedia.org/wiki/Focal_length
There's a simpler guide here, including some examples:
http://www.ezcctv.com/cctv-lens-guide.htm
Since you're probably using 1/4" CCD cameras, you'll find the most common lens lengths are 2.8mm, 3.6mm and 8mm. You should be able to obtain different lenses and swap them out in most cameras, but you'll have to focus them yourself, and some cameras will be easier than others to access the lens. Be particularly careful with outdoor cameras that may be weather-sealed - you don't want to damage the seals.