A value saying how much a hand weapon zooms in when the right mouse button is clicked. For the sniper rifle this is 0.1 (10x zoom), assault guns this is 0.5 (2x zoom), and values range upwards to 0.7 (for the Colt and WalterP38). Binoculars have a value of 0.2. The lower the value, the more the field of view zooms in.
Source and more details
As the MDT description says, the zoom increases with smaller values. This setting does not affect what is seen of the soldiers' body/weapon (see ObjectTemplate.SoldierZoomFov).