mental ray fog prob
 

hi
I am using mental ray for maya 1.5.1...Its a normal scene which is being lit by an HDR image by mapping the image onto a sphere as described in one of the mental ray tutorials ...i have add a Spotlight fog...now the problem is when i render the scene using mental ray ...the HDR image is visible in the cone area of the fog ...though i have turned off the primiry visibility of the sphere ...
Let us take a simple example ...just make a simple volumetric cone in maya and place a plane behind it ....render it using mental ray ...everything goes fine ...now turn off the primiry visibility of the plane and render it again ...this time though the plane should be all invisible but it is still being evident in the cone area ...this does not happen while using the maya renderer ....
i need some urgent help on this issue ...thankzz

jooji