If you are still a little unclear as to how you can render various passes with Solid Angle Arnold and composite them into a single shot, you are in luck. Lighting TD Arvid Schneider posts a look into creating and compositing Arnold AOVs.
Arvid walks through how to render the most used Arnold AOVs using Maya —The process is similar in any 3D host. Arvid shows how you can composite the AOVs into a single shot, showing how you can use the Z-depth pass for creating a “fake” depth of field effect. Arvid uses The Foundry’s Nuke for compositing, but the concepts will be similar in other pieces of software.
We recently had another tutorial author cover Arnold AOVs. 3D Artist Yone Santana covers creating render passes with Arnold using Maya’s Render Setup environment. Yone also discussed the pro’s and con’s of using render passes over AOVs.