Absorbing material inside a fog material

[elliotwoods]

Hi all

I'm trying to create a slide projector in fog.

I'm trying 2 ways to make the projector:

1. Pinhole - A plane with emission material (emission map is the imge i'm trying to project), the plane is inside a box with a small hole at the front
2. Transmission - A small light source inside a box. the front of the box is a flat cube of transparent material. The image to project is set as an absorbtion image map.

Both methods work in simple scenes (without fog). The pinhole is more problematic to work with (takes long to render if the small is hole, is out of focus is the hole is not very small).

So I'm trying to get the transmission method to work with. But what I'm finding is that:

1. The light and the camera must be inside the fog box
2. The absorbtion material has no effect whilst inside fog

I've tried the following but doesn't seem to fix:
* Creating an 'air bubble' in the fog around the absorbtion material
* Change the Precedence property of the fog and the absorbtion slide

I wonder if there's any tips out there to help with this?

Thanks and regards
Elliot

[CTZn]

hi Elliot, would there be a scene that you could share in order to get your setup inspected ?

[elliotwoods]

Hi CTZn

I've attached a sample scene here.
I seem to get no results at all when using Path-tracing Bi-dir when projecting through the slide, and the slide is ignored completely with Path-tracing

[thesquirell]

Not an expert here, but upon opening your scene file I can't help wondering myself these questions:

1) Shouldn't the precedence number of the fog medium be smaller then of the film one? In your scene precedence for the fog medium is 20, and for the film is 10. When I changed the film precedence to 22, I started to get some sort of a picture.
2) For your light emitter mesh, you should use light normalization, I prefer candelas. (luminous intensity=100)
3) Also play with the exposure duration, camera's EV, and ISO, and skip the Reinhard tone mapping when dealing with specific lights.
4) Forgot to mention it earlier. IOR of the film medium should be at least a little bit over the default value 1, otherwise the picture wont show up at all. Edit: It will show up, but it will be very low on contrast. If you wish to avoid changing IOR of the film, you could put a () lens in front of the film.

When setting the scene in this manner, I managed to produce some sort of a projection, but not sure if this is the projection that you were looking for. You should try it as well. I'm also curious on how to make this work, seems like a good test!