At first I couldn’t understand why caustics were not rendering.
The issue is that the ‘max photons’ option is not the same as cpu, in that the value of 0 apparently turns them off, whilst the tooltip is the same as cpu version and works as suggested.
Thanks for the report. This is probably by design, but we forgot to edit the tooltip. I’ve logged it (internal bug-tracker id: VGPU-6703) and will write back when I have more info.
Ok thanks, though it’s no issue for me. I just happened to notice so thought I’d mention it. Caustics are better with cpu if I need them anyway 
There is a bit of parameter adjusting to get GPU caustics similar to CPU ones since they work differently under the hood, but hey are significantly faster to render. Try increasing the generating light’s caustic subdivisions or/and increasing the search distance.
Yeah I did try experimenting a little but then had other tasks to complete. I’ll give it another go with the scene I explain below.
With this rather annoying (attached reference and result - I didn’t know what was causing the caustics, so had to guess and create random geometry to approximate) caustics situation recently, I found
a very quick method was to render a half decent really noisy blotchy version as an element, then simply upscaled it, which completely smoothed out all the imperfections and saved who knows how many hours try to let the renderer resolve it.
Whatever works
Oops, actually I need to amend that. I did do what I described, though in a separate version which I abandoned.
This version is even simpler…an extraction from the reference, then upscaled and comped. Sorry to mislead but glad I remembered lol
