I need just refractive caustics but it’s a real headache.
There are check boxes to disable one or the other or both. None of these options work for me and both reflective/refractive are rendered.
Even with both unchecked they are still rendered.
This is using photon mapped approach.
What is the hidden trick here?
The docs are useless as they don’t even show those options or mention them.
And then I find this page, specifically the header question asking about caustics in 3d max, then laughably being a Corona article and therefore useless. lol.
https://support.chaos.com/hc/en-us/articles/4528507676817-Why-is-it-impossible-to-completely-disable-caustics-for-individual-light-sources-3ds-Max
Are you referring to the GI caustics checkboxes? Because they are something separate (indirect caustics). I’m not sure if you can control the actual caustics by reflective/refractive - you can control an object’s contribution, though (receive/generate caustics in the V-Ray properties).
Please see attached.
Reading that mistitled Corona doc, I tried disabling the affect reflections options in the lights.
When doing that then those checkboxes’ functions are honoured, as shown in the other images.
So by pure luck there’s a way to make it work, though how anyone is supposed to infer this is beyond me, as there’s nothing in the docs explaining
any of it.
When you say that they’re not real caustics, then why are they rendered exactly the same when using that hack?
The shader is exactly the same and conforms to the options needed for ‘real’ caustics so I not sure I understand what the difference is.
Why are they something separate?
Also, it does not work when using a sun, only other light types. There is no affect reflections options in the sun…why not?
You can read about the differences here, and yeah, VRaySun doesn’t seem to work with GI caustics, only direct caustics.
Otherwise, the GI caustics options seem to work on my end without the need to disable the light’s ‘affect reflection’ (attaching sample scene). I’ve disabled the direct caustics so that they don’t interfere with the result (if they are active, they are applied on top).
EDIT: Changed my wording from real caustics to direct caustics.
sample_scene_GI_caustics.7z (41 KB)
Thanks for the link. It’s not the page I got when I searched, as I saw no info for that rollout, so maybe there’s a rogue page out there still that doesn’t contain it, or I’m blind.
Yes as I mentioned, you need affect reflections off to make it work. The results are basically the same as direct caustics but with that crucial ability to disable the reflectives, and with gi boost I can match the reference, so I have
a workable solution.
It would be helpful if it also worked with a sun but I guess I’ll have to live with what exists.
I said the opposite. Check my scene, the light there has ‘affect reflections’ active. Not sure why it doesn’t work in your scene. Attach it so I can have a look.
What are you referring to? The “affect shadows” or the black reflection. I’m misunderstanding something…
The affect shadows option. It needs to be unchecked/off in order for the fakes to work. In your scene you had it correctly unchecked when I opened your file, so it worked.
Well, yes. Refractive GI caustics (indirect) only work with it off. It’s the opposite, though: the “affect shadows” active creates the fakes (3rd variant of caustics). In our communication above, you mentioned “affect reflections” of the lights, which confused me.
I misread, apologies. It works for my purposes, so all good 
For clarity, I don’t care about having the default caustics really, it’s only that I have to match something that looks like some sort of retouched dodgy comp of 2d/3d and real video, so
have to figure out a solution for the various physically implausible bits.
The affect reflections thing must have been a false result I missed.
