looks like the coverage (or z-coverage) g-buffer channel is missing from vray.
this makes most of the other channel useless when compositing.
isn’t it under the ‘G-Buffer/Color mapping’ rollout?
exactly .. the coverage channel is missing from the g-buffer rollout !
that’s what I meant :?
now if anyone has more info or trick on how to get a z-coverage channel from vray I’d be glad to know.
for me without coverage; zvalue,objects or materials channels are totaly useless…
I don’t understand how this didn’t get in the top5 request until now..unless I missed something.
I have to add, that would make us very sad having to use another production renderer.. 
thanks in advance.
yeah, i have the same problem with the special camera type from vray, he doesn’t render the z-coverage, so that was impossible to create a dof in post-production.
But, with some tricks, you can have a render of the z-coverage, just select all your objects and give us a standart material with a falloff shader (type: blend distance) into the diffuse slot and instance it into the self-illumination slot (check to use the color in self-illumination slot). Then Turn off all your lights and the GI calculation. Now you can render your scene and you will have a faked z-coverage picture…
Welcome into the world of Mac Guyver 
i have the same problem with the special camera type from vray
are you sure you don’t mean z-depth instead of z-coverage ?
apparently coverage is absent from vray g-buffer channels no mater what camera you use..
the coverage channel stores anti-aliasing data at the edges of objects in the scene.
and is therefore essential for any postproduction job using the z-depth channel or materials channel or objects channel etc…
without it, no proper depth blur, no depth fog, no texture replacing, no material colorcorrecting etc.. without aliasing artifacts