Hello, i have some problems with the mtlwrapper. I use a domelight with a hdri map and a simple plane. I
t will not render correct, the plane is only black.
I use Vray 5 Update 2.2 . What i am doing wrong?
Set the ‘alpha contribution’ to -1.0 and you will need your dome light to be invisible also 
you set “matte surface”. So whats the background on that? May you try to set Alpha Contribution to -1 and ckeck your alpha. shadows are now being set there. in the moment the whole plane will appear white and there is no sense on that so far and as I know.
Hello thanks for your help. I just set the dome light to invisble and the Alpha Contribution to -1. No difference in the render.
I need this plane to have a shadow on a transparent background.
but you checked your alpha? The render itself shows of course no difference. Use a simple light instead for checking the technique. if that´s clear, get a dome light. vRay won’t render “transparency” like the small checkers in photoshop for instance. you have to do it in your comp program
Just checked the alpha, you are right. Its only a viewport “problem”