Hi,
I've encountered a problem in one of my projects and created a simple scene to figure it out.
What we have: plane 1000x1000 with default corona material, a simple tube with chamfer (highly reflective material) and corona light.
For first renders I've reduced max photons/iteration to 1k (5000k default) to see what happening GI/AA - 4. All renders are caustics render element.
1. tube radius 190 - everything fine.
2. tube scaled down, all good.
3. scaled down, all good(seems like, but not sure) had to increase photons to the default value.
and here the problem:.
4. scaled down to radius 2,2. Camera much closer and photons increased to 50000k - with default value I can't see caustics. Saved after 2 passes.
It looks like in this scenario no new photons generated after 2nd or 3rd pass - I can't see changes in photons distribution. And with each pass caustics become dimmer.
The second render is the same but at 50 passes. After some time caustics will disappear at all.
Now the even weirder thing. @ pass per render.
5. Same camera position as previous, tube scaled down. Caustics disappear much faster, it seems like they will go after 5 passes (don't remember now).
Next image - everything the same as in previous except camera - moved it closer. Now caustics not visible and disappear very fast. For this render I increased EV to 6 instead of 3.
So what I've found - at some point (size of objects, size of lights, the distance between them) caustics disappear over time instead of refining (looks like no new photons generated after few passes). And even weirder - it depends on how close the camera to those objects.
The scene I've written about at the start - a kind of studio render with some reflective objects. When the camera sees all scene - I have caustics that will not converge over time but disappear instead. But when I move the camera closer to see details - I don't have caustics at all or it disappears very fast.
I'm using last daily build - but I checked couple previous builds and v5 - the same problem. All of this true for default setting as well.
And the last one render - that seems like 20-30 min of render on the simplest scene, low res and 18cores... caustics still noisy. Is that normal?