Exposure changes when using metal groundplane

So I made some test renders using a hammered aluminum material on the groundplane. My boss loved the reflecty thing, and asked me to make an animation. It is quite simple; five or six things floating straight down one after the other to form an assembly. Here is the issue; the first frames start out with the groundplane almost white, yet as soon as each successive element enters the frames from above the scene gets a good shade darker. The exposure is locked. It is very distracting, and makes the animation unusable. I have changed the material several times, and it seems that any metal I use produces the same results. I finally had to go with a more matte material, which seems not to do it, but I really want the reflections in the groundplane, for the added wow factor. I also tried a glass texture, which seemed not to do it, but it looks a little odd, it’s not what I’m after.

Any suggestions?

Here is an example of what I’m talking about.

Here is a plane, with a material applied to it:

Now here is the same scene, with a few objects in it:

Notice that the plane is now darker, and it goes that way the instant any part of the object enters the field of view. So when animating, when something enters the scene from out of view, it creates a sort of darkening, like a light got turned out somewhere. Very distracting, unusable in a professional environment. The same thing happens when using a groundplane with a material. I haven’t had time to experiment with using lights, when I made a lengthy animation of an interior space with IES lights it seemed not to do it. But I need to bang out short animations with a minimum of hassle, and time is always of the essence.

Someone please experiment with this, I need to know if it is something endemic to the software, or perhaps just to me.

I have Maya and Max, but I find the interfaces to be clumsy and poorly executed. I would really like to stay with the simplicity of Rhino.

That is normal when changing the image so drastically. The change in color of the groundplane will change exposure. Normally you would adjust the brightness of the scene after rendering through the Adjust Image controls in the render window.