help with transparency and refelction.

[dibbers]

I want to re-create a std material with a Vray one. I want the material to be 100% reflective with 50% transparency. Straight forward I thought! Oh no!

If I set my reflection colour to pure white, it reflects 100% WHATEVER I set my refraction colour (ie. 128 grey). If I try with Frenel reflection on, it renders black!

What am I missing?

[joconnell]

Okay, if you have something that is 100% reflective then by definition you won't see anything else on the surface - it'd be like the object was made from a mirror like material or highly polished chrome.

The vray material is physically based like a lot of other renderers at this stage so it trys to mimic the real world properties of surfaces. One of those properties is that an object can never reflect more than 100% of the light that hits it - if you think of a mirror, if you shine a light on it, there is never a possibility where it can shine the light back brighter. It's pretty much the same with other objects - If you had a bright red object that was highly reflective, it wouldnt be possible for it to be bright red and 100% reflective for if it was indeed 100% reflective, it'd be a mirror surface and reflect the environment around it 100% - you wouldn't be able to see the red underneath.

Reflection will pretty much override any other surface attribute so it will as you've found wash everything out so you can only see the environment around it. The fresnel option can be a little tricky until you get used to it - as you probably know it make reflection weak at the front of objects and strong towards the sides based on the angle you are looking at the object from. There is a setting called ior in the vray material that controls the amount of reflection you see - a rough rule is that the more reflection you want, the higher you put this number (3 upwards for metals). Perhaps a more controlable option would be to put a falloff map into the reflection slot and then use the falloff curve control in the map to tweak your reflections.

Lastly, make sure your object has something to reflect in the first place. Shiny objects basically look crap and unrealistic if they dont have something to reflect so if you are using maxs default black environment with nothing around your object to reflect you're never gonna get nice results. Try using a gradient ramp in the environment slot with its coordinates set to spherical for a start or use an image / hdri map.

could you give us an idea what you want to achieve and we can give you some more specific pointers?

John

[dlparisi]

John's correct and got here while I was looking this up. Here's the quick explaination from Vlado...

V-Ray automatically tries to preserve enregy in the VRayMtl, so if a surface gets more reflective, it gets less refractive (more opaque) so there is no need to do anything to force that behaviour.

He explains it all here.

[dibbers]

thanks. That does make sense.

I want to create flat glass for architecture, BUT, I want to control the Fresnel effect manually in PS.

If I reduce the reflection a bit so the refraction amount will kick in, that should help, but doeas the deffuse need to be blck? Mmmmm.

[joconnell]

Yeah for glass I normally use a black diffuse, white refraction (or near white) and a white reflection with either fresnel falloff or a falloff map - you may be better off lookling into rendering your reflection pass seperately so you can simply use a blening mode to comp it over in photoshop and have a lot more flexiblity with masks.