Excluding Objects from Alpha Channel

[allmixtup]

Objects in my scene (that aren't even linked to any lights) are showing up as part of the alpha channel. Some of these objects need to be there to mask their shape onto the objects that are lit. However, some of the objects need to be excluded from the alpha to make some 'holes' where other layers can show through.

Is there a way to designate which objects are recognized by the alpha channel generation?

Have been doing some digging and am finding some vague references to the "use background" settings but can't seem to nail down any concrete info.

As you can tell, I'm a noob so please assume the worst about my level of experience.

Thanks

[joojaa]

Yes its the matte opacity.

Tough i think you want to use the use background shader wich is a total blackhole shader even in this respect. Offcourse any other shader will do but use background is designed so it can take shgadow and reflections in account.

[allmixtup]

Thanks Joojaa.

Just in case there are any noobs (like me) checking this out, let me explain this a bit more.

In the hypershade window, one of the materials available is called "use background". Drag it into the work area and assign it to all the objects in your scene that are not supposed to be rendered out for the current layer.

The objects with the 'use background' shader will still act as mattes (if they pass in front of lit objects) but they will not be rendered out as part of the alpha channel.

Hope this makes sense. Sorry if I'm using the wrong terminology but--I'M A NOOB!!!