Question mental ray Mist (Lume) Shader

['lectric eye]

Hi all, I hope you had a good xmas and are tightly clutching your party poppers in anticipation of 12 midnight tonight... unless you're Down Under, I think it's already 2009 there. ANYWAY, I'm having trouble using the Mist shader in mental ray. I'm trying to set it up so that close up to the camera the air is clear, and further away the mist is dense.

In my scene the Y axis is the forward/back axis, so after putting a Mist shader material as the "Volume" camera shader map in the Renderer tab on the render scene dialog, I've checked the layering and realistic falloff options and entered the falloff distances, and then entered 1 in the middle "Plane Normal" box and 0 in the other two, as this should be the Y axis. However I seem to get a lot of mist right up close to the camera no matter how much I play with the values.

I think the problem is that the mist always starts at the camera's position and thins out away from the camera along the normal you give it, as when I enter 1 in the X Plane Normal box, the mist starts on the ground and thins out up the screen. Does anyone know if you can invert the values somehow to get the opposite effect? I tried entering -1 into Plane normal but this doesn't seem to change anything.

[jasonmclaren]

Go into Max's help and search for "Mist Lume". Scroll down a ways and click on the Mist shader. This will bring up another help with the details of the shader. According to the documentation the only control you have over the fog with "Realistic Falloff" is the overall density of the fog.

Just from reading the help and not trying it myself I would try the "Custom Falloff" option and adjust the falloff curve yourself. In theory this should give you the control you need to get the effect you want.

['lectric eye]

Thanks for that, I didn't notice that entry in the help file the first time I searched it. I kicked myself when I found out the way to change the direction of the mist - You're meant to enter an angle in degrees into the plane normal input box. Makes sense as it's a normal. I entered 90 and the mist falloff direction changed from down-up to forward-back.

[jasonmclaren]

Good stuff. Some options in other shaders expect a value between 0 and 1. Can be a pain when you forget which ones.

Cheers :-)