bagrat: It is realy hard to describe what is proper. Think of the compter screen as a window. If you get closer to the window you can see a bigger angle of items outside the window. So what Field of view (i.e Zoom) realy depends on how far you are sitting from the screen.
What the default is , realy dosn't make much difference, most games use about a 45 - 68 deg FOV, this is equivlant to pressing Z and not adjusting the zoom we would have 57 deg . We default to 90 degs which gives more overall SA but less detail on planes.
The real kicker is that in real life your eye has almost teliscopic view in the center of your vision, hand hardly any detail at the edges, and obviously there is no good way to do that on a computer screen.
HiTech