Reflection/Refraction Pass
Overview
By doing a select attribute pass and checking only reflection or
refraction, you won't get proper raytraced reflection/refraction.
Setting up the render job
Use whatever settings you like for your render job. You'll need at
least these two passes to extract the reflection/refraction information.
The noref Pass
This pass does
not have reflection and refraction checked, but is a normal render
otherwise.
The ref Pass
This pass is a
normal render.
Compositing the two passes
In Photoshop (or
whatever image editor you prefer), paste the noref pass on top of the ref pass. Set the noref pass's layer mode to
"Difference".
Compositing the reflection pass with your image
Paste the reflection pass on
top of your image and set its layer mode to "Linear Dodge" (aka "Add").