Hey, Steve Green!
Did you solve that problem you had with an object you wanted to render without being affected by lighting in the scene?
Without actually having tried this, my guess would be to right-click the object, choose Object properties-mental ray and then uncheck everything there, basically. And of course, for every light, Exclude that object from receiving illumination (I’m not sure you can do that for all lights, but…). That should keep the object un-illuminated? Then, self-illuminate the material. I assume this is about what you’ve already tried, but here’s what I’d do next:
If the Exposure control still keeps the object dark, try increasing the output of the diffuse map (or the self-illuminaton map, if you use one). I’d try increasing the “Output Amount”, the “RGB Offset” or the “RGB Level” for the diffuse map and see what happens.
If this doesn’t help at all, maybe an Ink’n Paint material would work? I don’t know if that one would work in Mental, but it’s a thought.
Also, I know Mental can output just the diffuse component, because it is one of the elements you can render out in Render Elements, but that one gives you the entire scene with just diffuse shading, not just one object. Close, but no cigar…
So, did you solve it, and how did you do it? Just curious!