   Z buffer and long distance
  Hi, with direct3D9 i have noticed that the Z buffer doesn''t affect the objects that stay at a long distance from the viewpoint, and at that long distance every object is renderized without take depht into consideration, maybe the distance of the objects from the viewpoint is greater than the size of the Z buffer, or maybe something else...Someone know this problem with direct3D9?ThanksKev 
  The depth buffer''s precision decreases the further away something gets from the camera. You''ll either have to make the near clipping plane farther away or the far clipping plane closer, or increase the depth (probably from 16 bit to 32 bit) of the depth buffer   Game Development Wiki;  Not all video cards support a 32 bit z-buffer.  For many the maximum is 24 bits. 