How to Select the Lens
Go to each location you want to view with your surveillance cameras. Bring your digital camera to each of the locations. If you don't have a digital camera this is a good excuse to get one. The camera should have a zoom lens that has mm markings on the lens so you can record the right mm for the lens.
Again, decide where you would like to place the camera. Place the digital camera as close as you can to the planned location of the video camera. Take a picture of the view you would like. This is will define your field of view. Record the lens position (so you can later select a similar mm lens). Measure how far away the camera is from the field of view at each location. Record how wide an area you would like to view. This should be determined by the picture you took using the digital camera. The distance to the area and the width of the area define the lens. You can use the lens calculator at http://www.kintronics.com/iqinvision/lenscalculator.htm to determine the lens mm.
If you decided that you need a PTZ camera, you can still use the lens calculator to determine if the zoom lens is within the range you need. For example some cameras have a 10X zoom (4.2 – 42mm) and some have over 22X (3.9 – 85.4mm). Use the lens calculator to see if the area you want to see fits in the range of the camera you select.
You can find a lot more information about cameras and lenses at the kintronics web site