Hello everyone, please tell me something about the position of cameras :
1. In a tower (office, commercial, residental...), what areas required close-up view? what areas required general view?
2. In common type of cameras, what type of lens are used (2.9, 4, 6mm...)?
3. In general view, how much is the distance from camera to the scene?
Thank you very much!!!

It depends on many factors.

Some camera's may be required for overview shots, some for recognisation, some for identification, all have different purposes and requirements.

Some may be overt, some covert, some indoor, some outdoor.
Some fixed, some pan/tilt/zoom.

Different risks require different solutions.

A site survey from a pro cctv company should identify what is required.

Just like Kensplace said, it depends!

Generally speaking:

3.6mm 15m
6mm 20m
8mm 25m-30m
12mm 40m-60m
25m 100m-120m

Hope it helps and here coems a useful website for calculate lens: http://www.videologyinc.com/lens%20foca ... ulator.htm