Light problem in zooming animation

Hi guys, maybe someone could help me with this problem.
I'm working in 3ds max 2015 and I have to create some zooming animations: unfortunately while the camera is moving toward to the object, but it is still far away, the lights and shadows on the object become dark randomly and every frame has a different light result.
Also with static renders I have the same problem, when I'm far from the object It becames darker.

Both mentalray and standard materials have the same problem.
I attach an example with 3 frames of a simple animation.

Thanks in advance.

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