Object Alpha over mental ray? where?

[romanus]

Hi guys,

Here at ingreme we're trying to change to mental ray, but there are simple things that are getting our nerves :) Natural thing for a starter, of corse!
We setup a matte object using matte/shadow native max material. Then we added over the mental ray connection - surface - shader list with bump and reflect materials... it worked perfectly! We had the original matte object + reflection matte.
But then we turned on depth of field (mental ray) at camera and this matte/shadow material seems to have a bug when u turn on depth of field...
The other aproach i tried already, it's to use render element - reflection, but i don't know why, it appears all black and with the matte of the original objects. Any idea why it appears all black?

Any help on this would be great :) Since at v-ray we have an option to make alpha -1 at any specific obejct in the scene.

Of corse we can make two separated renders. One with all objects reflecting to a black surface so we can add reflections in post and then make this reflective surface a matte object and render it again to subtract matte from all the objects. But this doesn't seem the best way to do this... maybe i'm missing something over render elements...

cheers all and congratulations for this forum... hope it will be a major success!

[romanus]

To better illustrate problem, i've attached some jpegs...

1 - Original render

2 - Matte1 - The matte i get using mental ray material to make this nice reflections (it's a simple plane)

3 - Matte2 - The matte i wished for. I had to make another render for it.

So, u can say, but u already found the solution... the problem is that this will be a shot with thousands of ppl, with motion blur and dof... so all the less renders i have to make, the better :D

thanks again ppl

[romanus]

well,

I've found that reflection element works! The problem is that i was using matte/shadow material and daylight with ies sun... it seems that for mental ray we have to use and abuse using only mental ray lights and materials ;)
But i still ask if anyone knows how to make an object render with alpha contribution -1...

thanks for the attention anyways :)

[NessunDorma]

Hi romanus, having the same problem now, want -1 alpha on certain objects, did you ever figure it out?

[strangerman]

Why don't you try the matte/shadow/reflection shader that comes with mental ray? it works quite well for this purpose, just be sure to set the alpha value to 0 in the color slot.