caustic problem

[stevesideas]

Hi Guys,

I have a problem with caustics. Im currently working on a project that invloves having a liquid in a glass. I thought I would try to increased the realism by turning on caustics. Unfortunately when I do, the glass changes from refracting the background behind it to a grey looking material. Anyone know why this is happening ?

Ive attached the caustics off and caustics on screen shots. Also attached the glass settings. This happens even when the liquid is not present in the render.

[Aldaryn]

This is only related to losing the contrast in the shadows underneath the glass, so the refraction won't be as rich as with the other rendering.
Also, if you are using large softboxes to illuminate the subject, caustics won't be as pronounced as you would "expect".

Be sure to switch off affect shadows when caustics is on, to have an accurate energy transmission, and I suppose you should use a diffuse color other than white for your glass. Also, some fog might help to bring in some contrast to get some life into the refractions.

Best regards,
A.

[zeronove]

I thought when photons caustics is on, vray doesn't take care of the affect shadows checkbox, it should override that info, isn't it?

consider that I'm a newbie in the caustics world

[stevesideas]

Aldaryn, thanks for the reply.

Couple of things though..I am using a vray dome light to give the whole scene a global lighting feel. Then im using a spot light from an angle to create the caustics. Only the spot light has caustics on the the vray properties.

So, this light does not have affect shadow...maybe I should change the spot light over to a vray sun ? so that I have that option...

Regarding the material. I thought white in the diffuse slot was ok for clear glass..my client doesnt want coloured glass. Also, the fog..what settings would you recommend there. If I add a fog colour other than white it will colour the glass, which is not what I want. Can I add white fog ?

Cheers

Steve

[zeronove]

affect shadow checkbox is a material setting not a light one

[Aldaryn]

I thought when photons caustics is on, vray doesn't take care of the affect shadows checkbox, it should override that info, isn't it?

consider that I'm a newbie in the caustics world

No, there is no override. And since caustics is used quite locally in many cases to spare resources, it wouldn't be wise to apply a global override.

Best regards,
A.

[RErender]

zeronove is correct, affect shadows is ignored as soon as caustics are turned on.

[Aldaryn]

Oh, my bad, didn't know this was changed along the way. Thanks for the info! And this might just explain some strange behavior I had with an older scene I had to re render a couple a days ago.

Hmm, still seems to me as a bad idea, or is there a way to turn this off? You see, the scene I have to re render has a single small pool, the Vraysun's caustic photon emitting radius is set up, so all the photons from the sun will hit only the pool's surface, to use as less photons as possible for a sharp and clear caustic pattern at the bottom of the pool. Now, other parts of the scene don't really need caustics at all, since all refractive things are just window planes there, and it would require a hell lot of photons to get sharp caustics/shadows from the Sun all over the 2000 sqr m building.

Or using localized caustics will always leave me with some compositing to do in the new VRay builds?

Best regards,
A.

[RErender]

It has always been this way,I remember some posts about it but I'm not sure if Vlado ever explained why, if he did it be down in the archives from 2004'ish probably.

One thing you might try is turning on GI caustics if they are not already, other than that you could set up some more focused lights to emit photons where you need them.