The fov_switcher_v13.zip file you have requested: Clear Sky / Utilities / FOV Switcher - 16.96kb is not available. Perhaps try browsing all files for the game S.T.A.L.K.E.R.: Clear Sky and upload any files you want to share or are missing. This is the only information we could locate:
Special patcher changes FOV (field of view) to 90 by direct editing of the xrgame.dll. With expanded FOV (Field of View) appears the sense of dynamics at movement, other perception of surrounding, the world seems more volumetric.