I forgot to mention that if I set the limits so that I have a transparent background, I also lose my smoke.
Anyway, I’ve found that if I switch my domain object to use z-transparency then I get my transparent background back. Adjusting some settings gives me something approximating my original, but it just isn’t of the same quality delivered by ray tracing.
So, I came up with the idea of using ray tracing and the compositor to remove the black background. My understanding is that I can send each pixel’s z-value to the compositor. The black background must have a different z-value than the image components, so I thought I would be able to replace those pixels with a transparent value. I’ve played around with the Z Combine compositor node, but haven’t had any luck.
Is this possible? If so, how. Thanks.
Edit: Actually, on second thought, that won’t work, because the smoke won’t have any transparency. If I can’t get transparency of my smoke domain using ray tracing, I’ll just need to accept the lower-quality z-transparency render.