ok, here is a description of the problem:

i think i have found a bug, 3ds max design 2010 64 bit, latest hotfix installed, vista 64.
-create a simple scene with a ground plane and a pool. set the water surface to generate caustics
-check generate caustics in render setup, make sure all objects receive and generate caustics is unchecked
-add a daylight system to the scene and some photometric lights to the pool
-in the object properties of the sun and the lights, check generate caustics
-also make sure the water material is configured to generate caustics
-turn on fg and gi
-render. everything should be fine and here it is
-now uncheck generate caustics (or check exclude from caustic generation) in the object properties of the pool lights
-rerender and look at the mr message window and you will see that our pool lights are still emmitting caustics photons

you can also test this with the attached scene.

	Attachment
caustic_bug_2.zip

I don’t think it is a bug.

The object properties’ “Generate Caustics” is a flag indicating that the geometry of that object should have its shader confronted with emitted caustic photons.

A light has no geometry, so this parameter is pointless. And it is incapable of generate caustics. It emits caustic photons, which is different.

To correctly isolate a light from emitting caustic photons, you need to set, under its “mental ray Indirect Illumination” rollout, the “Caustic Photons” multiplier to 0.

It is wiser to do so, having a specific light with no diffuse or GI contribution to the scene, dealing only with caustics effects. This way, you can boost the caustics and not deal with Light intensity or GI conflicts.

RodBiffi 06 June 2009 10:50 PM

I don’t think it is a bug.

The object properties’ “Generate Caustics” is a flag indicating that the geometry of that object should have its shader confronted with emitted caustic photons.

A light has no geometry, so this parameter is pointless. And it is incapable of generate caustics. It emits caustic photons, which is different.

To correctly isolate a light from emitting caustic photons, you need to set, under its “mental ray Indirect Illumination” rollout, the “Caustic Photons” multiplier to 0.

It is wiser to do so, having a specific light with no diffuse or GI contribution to the scene, dealing only with caustics effects. This way, you can boost the caustics and not deal with Light intensity or GI conflicts.

as stated in the documentation, the generate caustics flag obviously has no influence on objects that cant generate or receive caustics like cameras etc. but as lights can emit caustic photons the generate caustics flag does make sense here. (it would be better to differntiate between geometry and lights here to avoid confusion, like it would say in the light object properties ‘is caustic photon emitter’ instead of ‘generate caustics’) it is also clearly stated in the documentation:

Important: For caustics to render, you must also make sure to set up these other conditions in your scene:

At least one object must be set to generate caustics. This is off by default.
At least one object must be set to receive caustics. This is on by default.
At least one light must be set to generate caustics. This is off by default.

The settings for generating and receiving caustics are located on the Object Properties dialog mental ray Panel.

you will also see this described in any useful caustics tutorial. lights are meant to generate gi photons by default, but not caustic photons. and that makes sense, since in almost all the scenes i work on i dont want the majority of lights to be caustic photon emitters. say i have 30 lights in the scene and only 5 are meant to be caustic photon emitters, instead of editing 5 i have to edit 25 lights now.