Placing a tunnel around the tank, we see a situation that is even more dramatically different. This is one that I would just avoid with Poser 7. I wouldn't even try to do this.

With IBL, we can sort-of get the ambience right for things outside the tunnel or deep inside the tunnel, BUT NOT BOTH AT THE SAME TIME.

Is that clear? IBL cannot capture ambient lighting in a varied environment. It is fine for a solo figure standing outside, it is not fine for anything involving canopies, tunnels, caves, AND open to the sky in the same render.

The tank here is partly in sun. The shadows part should be picking up some open-air ambience as you look farther toward the rear. Instead, it is homogeneous. Also, observe closely the lack of gradient on the tunnel wall and the ground.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)