Aslak Kjølås-Sæverud

I assume you've read the karma lens docs? https://www.sidefx.com/docs/houdini/solaris/support/karma_lens_shader.html [www.sidefx.com]
There are some sample files that make use of custom lens shaders, they might shed some light on how to get it to render to disk.
I feel like it was working when I was playing around with a custom lens shader in h20.5

edit: Here is the one that I built, also using vop nodes https://www.sidefx.com/forum/topic/94084/?page=1#post-424757 [www.sidefx.com]

Are you running 21.0.513+?
This was added in 513:

Might fix this


I also think @tamte is correct that you should be able to fix this by modifying the parameter

Shadow linking is in the light linker
[www.sidefx.com].