How do you handle iteration count for a Mandelbrot zoom video?

[laser blaster]

For anyone who's made a Mandelbrot zoom video, how do you handle the iteration count as you zoom into the fractal? Surely you wouldn't use one iteration count for the entire video, as that would be a waste of render time. So, do you set the iteration count manually at certain keyframes, or use a formula to automatically determine the iterations for each frame?

I'm not asking for help with any specific software, I'm just looking for a general answer. Thanks.

Edit: 15 views immediately after posting??? This website is screwy.

[panzerboy]

You mean maximum iteration count?
I set it to the largest value needed.
The end of the zoom movie with large iteration counts and high precision arithmetic is where you spend most
of the rendering time.
So optimising the maximum iteration count as you zoom doesn't gain you much.