Maxwell Render | Official public forum

Can someone explain to me what the "trick" is when placing a light source/emitter behind something like frosted glass in order to scatter the light travelling through the surface?
I've been trying to simulate simple real life photographers techniques with foils and frosted glass or even simpler a lamp shade like diffusor but the Light never manages to come through!?!

Joris

If you are using a glass material with an ior value of more than 1, you are creating caustics that will take a long time to clear. I would suggest using an mxi emitter to simulate the effect or use a frosted AGS material.

Bubbaloo,

this is what I've been doing to get around it so far, and it works okay but I can imagine having alot more control over my lighting situation if I was able to use the Multilight function with one or more lights behind a diffusor.

Nevertheless I'd like to understand the technique used when rendering a lamp with shade.
I have 24/7 access to a small 16-core xp64 farm which is all mine, so I won't have to worry about renders taking upto SL 20 or so.

Joris

Bubbaloo

Im trying to set up materials on this and see your mention of frosted ags.
How is this set up ?
.....Is my material fundamentally flawed ?
The bdsf is duplicated in additive mode to give the frosted glass more intensity

JorisMX wrote:Bubbaloo,

this is what I've been doing to get around it so far, and it works okay but I can imagine having alot more control over my lighting situation if I was able to use the Multilight function with one or more lights behind a diffusor.

Nevertheless I'd like to understand the technique used when rendering a lamp with shade.
I have 24/7 access to a small 16-core xp64 farm which is all mine, so I won't have to worry about renders taking upto SL 20 or so.

Joris

I think using AGS would be the quickest rendering, but sss for a lamp shade would probably look the best but take a long time to clear. Make sure it is not your only light source in the scene. Someone, I think Herve, made a lamp shade recently using sss but I can't find the thread.

pipcleo, use the wizard to create an AGS material, then add roughness and change the transmittance color. It will clear faster than glass. I would stay away from duplicating a layer at 100% in additive mode or expect unrealistic results.

somehow I don't think AGS will work like you describe Bubba', based on the issue I discovered here: http://www.maxwellrender.com/forum/view ... sc&start=0

seems setting nd=1.0 is still causing caustics to be calculated…

Joris--the best bet for what you're after is either a bit of surface roughness (is the material really scattering light internally, or is it a function of the surface prep??) or SSS and a lot of time

JorisMX, a sample photo of the effect you are after would be very helpful!

I gave up on ags for this after experimenting for a day.It seems impossible to get an intensity to the color of the frosted glass.
Also the frostiness does not seem to look right.

Thats why I asked about your suggestion for an AGS recipe.
My material above does seem to produce a fairly good result...
will post it soon.
SSS just takes waaaayy to long to clear

Kurt, I have no access to the pictures I took from a real life photoset right now, so these googled and sketched images will have to do:



This is basicly the main thing going on.

I have tried using gradients made in photoshop converting them to mxis and using them in emitters
This doesn't give me the flexibility I desire though.

For Example using 2 or more Light Tubes and moving them to the sides or center of the diffuser you can achive a nice smooth light gradient
which will help sculpting the light that hits the Object you're trying to light.
Also having an other "big bulb" tilted back gives nice gradients that have a sharp bottom and smooth top,

Having either 2 or more light sources or perhaps the same source in various angles and positions would result in great flexibility using Multilight.
Otherwise you're in the dark (ha...ha) about what your lighting situation is untill you let it render long enough,
just to find you will have to move or change the angle of the light source.

The X obviously marks the spot of the Object we're trying to light.
Please note that I made this one sketch as a simple example, the "big bulb" is a technique I would rather use on a diffuser placed
behind the Object giving us a nice Background that lights the Object and gives nice rim light also.





I hope this is helpfull!

Joris

You're going to have long rendertimes for any lighting setup where the light has to pass through another object before it hits your subject. There's no getting around that. I have seen great setups like the one you posted from google that people here have done with mxi emitters. But you're right, it's not flexible enough for what you want to do with multilight.

If somebody could post a scene where they lit a simple object through a plane would be great. Still everything on the other side of the surface stays dark when I try to simulate this kind of setup

Joris

I agree with Bubbaloo. You will have problems with getting clear and noise-free rendrings with this method. It would problably be a lot faster to make a number of mxi emitters that you could experiment with until you have the perfect setup.

Another method you might consider that gives you the flexibility you are after is having a gradient by using reflected light on a surface - rather than refracted caustic light. Just place the emitter under your scene to light up a panel from a tilted angel. No need to have a semi-transparent surface. I used this method in this fluids test:

Kool idea. I never thought of that. Then he could add multiple emitters and adjust with multilight.