Below are some commonly asked questions with regards to changes in Arnold 5.
Where is the Standard shader?
Is the Standard Surface shader energy conserving?
Where is 'Refraction Roughness' in the Standard Surface shader?
Where is the specular GGX microfacet distribution?
How can I control the index of refraction for transparent materials?
How can I control Backlighting/Translucency in the Standard Surface shader?
IOR and Metalness appear to do the same thing. Why use one over the other?
Where is the Skin shader?
Where is the Hair shader?
Where have the UV parameters gone?
Where is the Volume Collector shader?
How can I use OSL shaders?
Where is the Shadow Catcher shader?
ASS Files
Although the syntax of the file format hasn't changed at all, .ass files generated with Arnold 4 may not render correctly with Arnold 5 and so should be avoided. Likewise, .ass files generated with Arnold 5 may not render correctly with Arnold 4.
Sky Shader
The sky shader is deprecated and will be removed from a future release. You should instead use the visibility settings in the Skydome Light.
Skydome Light
The Camera visibility in the skydome light replaces the need for creating a sky shader and carefully setting its visibility attributes to avoid double counting. The Skydome light shows up in the indirect AOVs, not the direct. It can be changed to the direct light AOV by setting the light's AOV to "default" to place it in the default light group, or another name for some other light group.
How can I add a custom color space?
You must set the OCIO environment variable to the config.ocio color profile path before starting Houdini. Houdini will then pick up the color spaces in the config and make them available as options for rendering color space, texture input color space and driver output color space.