Lens refraction issue

[carsten_astheimer]

Hi

I'm trying to find out what different light patterns I can create with different lenses, but no matter what shape I place in front of the light it doesn't seem to have any effect on the light rays passing through it? Ie when I place a flat surface in front of the light, the light projection on the surface is the same no matter what differently shaped lens I place between the light and surface?
I've attached some images (along with material, light and render settings) to explain better.

[Grigio18]

can you show some real photo reference , I want to understand what's your goal.
By the way, I guess you should start creating a physically correct material, and probably activate caustics to obtain the result you want.. but fist show me a real photo reference.

[Micha]

Caustic enabled are definitely needed for this kind goal. Some tutorials should be available at the web.

[carsten_astheimer]

Thanks for getting back to me!

This image shows what I'm aiming to achieve in principle - the light from the candle is being distorted by the bowl (acting as a lens) before it hits the surface behind.
Is that the caustics in global illumination? I had that on with reflective and refractive caustics enabled and it made no difference.

[carsten_astheimer]

If this helps here's the geometry I've set up. The second screenshot maybe shows the issue better - the light that I'm using is just being projected directly onto the back surface and the lens geometry is doing absolutely nothing.
With regards to the material I've just used the Vray standard material for glass, does it not replicate the real material well enough?
I've gone through a couple of tutorials but they've all been for older versions of vray and seem to have slightly different controls, I'm having trouble finding where the tools are on the newer version.

[Micha]

Never I really used caustic, but I would take a spot light so that the photons are more focused. Than maybe it helps to shoot more caustic photons.

But ... I can't find the global caustic option anymore. Maybe it get lost. I can find GI caustic only, but this isn't needed here. I hope the Chaosgroup team will help.

[carsten_astheimer]

Unfortunately the issue happens with every kind of light I put into the scene. In this one I used the rectangular with a directionality of 1 since it won't scatter no matter how far away the surface is from it - ie the only scattering should come from the light passing through the lens.
I've found a slightly different tutorial here https://www.youtube.com/watch?v=_5zW...ancarloDiMarco that I'm working through, hopefully the answer is somewhere in it.

I'll make sure to post the solution if I find it!

[Micha]

Did you find the global caustic control? If not, a workaround could be to save the v-Ray option and look for the option per text editor. So, I hope, you can enable it.

[Micha]

An other idea - I tested how good GI caustics are working and this is the result. And it works in GPU mode too.

(Don't forget to disable the max ray intensity if you need high intensities.

[carsten_astheimer]

I think I've found it, but interactive rendering has to be disabled. There's a tab called "Photon Mapped Caustics" that seems to have the same controls as global caustics, I'll include a screenshot.

That's awesome you've got it working! I've had a go at replicating it though and it's still coming out with the same result as before. Would you mind screenshotting your render settings and I'll make sure mine's exactly the same?

[carsten_astheimer]

Here's a slightly different view with and without the lens present

[Micha]

I found the photon caustic options now too.

Did you disabled "affect shadows" at the refraction layer of the glass (you need to enable the advanced options of the glass)? It's needed for photon caustic and GI caustic.

I tested the photon cautsic and it works at default values, only I need to increase the spot light intensity.

[carsten_astheimer]

Maybe it's something up with my Vray... This is what happens when I disable affect shadows

I'll try another fresh file to make sure all the defaults are fine and change only those couple of switches

[Micha]

Here m test file.

[carsten_astheimer]

Well... It's certainly doing something now

I set up a new file with the defaults, made those couple of changes and that file worked. I then copied the settings back into the file that wasn't working (there were a few values that were completely off the default, definitely don't remember messing with them so don't know what happened there...) and this is the result!
Obviously the lens is doing some crazy stuff with the caustics at the moment, but it is doing something so I can start refining the geometry.

I've included screenshots of the setup in case anyone else has the same issue.

Thanks very much for all your help Micha!