I’m trying to render a little video with Maya. But after the Batch render, i only get frames with black backgroung, instead the effect from Physical Sun & Sky.
I read something about disabling the Alpha channel, but i don’t know how to do this.
I will appreciate any help. 
You are likely saving a png file which sees a black alpha and decides that the RGB is all transparent and shows nothing.
The actual sky is in there, if you use a viewer that doesn’t automatically use the alpha you will see it.
A few options.
1)Whatever software you use to make your movie has to be able to ignore the alpha.
2)Render with another format like targa that doesn’t automatically use the alpha.
3)Set the framebuffer to “RGB byte 3x8 bit” which will render a png with no alpha.
framebuffer is in rendersettings->quality-framebuffer->datatype.
Just to explain further. When you create Sun and Sky, any per-existing cameras will have two shaders attached to them. Any cameras created after the fact need to have their connections updated.
You can easily update those connections in the Physical Sky node.
[img]http://i.imgur.com/gC7j9d5.jpg[/img]