Be aware that some capture cards work with the analog or digital signal only. Some with both, which are more expensive. I don't know why they all don't do this. Most of the cameras will let you turn it up or down manually. But the slower shutter speeds are a big plus.
Many cameras only offer the auto feature.
Usually works just fine. But it's nice to be able to manually adjust this for certain situations. But it's tough. Better to zoom at your slowest speed, then give that clip some slow-motion in the editing. This won't work, of course, when your actors are speaking.