In general the trick is to add the clouds (either an image or a node) to the physical sky “Haze” value as Master Zap indicated in his blog. To achive that in Maya you will need the following. Maya nodes = noise, multiplyDivide and luminance. Connect as follow noise out color > multiplyDivide input multiplyDivide [...]

Using the mib_amb_occlusion is a fast way to produce an Occlusion pass. It has a great advantage when it comes to render time, as well as the composting process. Let’s have a closer look at the node attributes. Assigning to a Shader. The mib_amb_occlusion node can be assigned to a shader in number of ways. [...]

Transparent or semi-transparent shader will produce a semi opaque alpha, if it was rendered with a Maya shader The following image is a Blinn shader rendered with mental ray, you can see the semi-opaque alpha However if you assign a dielectric material or a Glass mia_material, you will get an opaque alpha.   To correct [...]