Volumetric scatter shader does not show light focused through lens correctly I am trying to make the light from a convex lens shine through haze in a volumetric scatter cylinder like this: https://www.behance.net/gallery/53917965/LENSES-TEST
I can see that my lens does concentrate a beam of light on the plane below the lens, however the volumetric cylinder below the lens depicts a perfectly even distribution of light...

Is there a way to make the volumetric light look like the scene linked above? Here is a wire frame to make it easier to understand how the scene is set up...

And the node setup for the volumetric scatter cylinder...

Here is how it looks if I enlarge the volumetric cylinder enough to envelope the entire scene. There should be a narrowing beam of light below the lens...
It is working, it's just not visible (yet).
Try using the branched path tracer to sample more volume bounces per sample:




Switch to the Branched Path Tracing integrator
Set the number of volume samples to something large (you may also want to increase the samples for some of the other passes as well)
Set the number of Anti-Aliasing samples. These correspond to the number of initial samples cast from each pixel (See What is branched path tracing and how is it useful? for more detail)
Note the total number of samples per pass (21000 volume samples, and still not nearly enough!).


Here is your file rendered with the settings shown above (to get a better caustic on the diffuse plane, try increasing the number of diffuse samples a bit):