I have a model of a room containing a 1/10th scale model, containing at 1/100th scale model, containing a 1/1000th scale model.
I move the camera from a start position - looking in through the window of the 'top' room - to the frame before an identical view through the window of the 1/10th model. If I loop this, I get an 'infinite zoom-in'.
(The smaller models are to provide convincing detail through the window. I don't zoom down to them).
To make the camera movement smooth - an apparent 'constant' speed in relation to scale - I need exponential change in speed in X & Z. Of course, the exponential curves in Blender's graph editor don't do this, they only offer an exponential change in displacement.
As a consequence, Blender's exponential interpolation starts 'too fast' and ends 'too slow' to look like a constant speed: The exponential curve in displacement is going from 10X to X, but the velocity is going from N to zero, and I can't see any parameters to adjust this.
I can get an apparently constant velocity (i.e. dropping exponentially from 10xN to N) across a clip by placing the keyframes of the exponential change in position some distance outside the actual loop. However, while this loop then looks fine, I can't then put any action in just before or just after this action, as there's the gap needed either side before the keyframes.
I could animate up to, and then after, these keyframes, then remove the unwanted frames later, but it would be nice if there were a way to adjust the parameters of the exponential curves so this wasn't necessary.