Re: Undercrank vs. "slow shutter"

The answer to your question lies in the difference between shutter speed and frame rate. Shutter speed is as you are used to, slow speeds allow more light but are subject to blurring any moving objects. High shutter speed stops motion, but, there is less light to expose with.

Now, frame rate is how many images you capture per second. If you capture images at, say, 24 fps and play them back at a different rate, you'll either speed up or slow down the apparent motion in the film. For example, if you play it back at 30 fps, it will appear to be 1.25 x faster. This is overcrank. If you play it back at 12 fps it will appear to move half as fast, aka slow-motion. This is undercrank.