When you zoom in/out on a traditional video camera, the zoom is very smooth because it’s controlled by an internal motor—you just push a button and it smoothly zooms in or out, giving a nice professional look. The problem is that there’s no internal motor on your DSLR—you have to zoom by hand, and if you’re not really smooth with it, and really careful while you zoom, you’re going to wind up with some really choppy looking zooms.
In fact, since it’s so tough to get that power-zoom quality like we’re used to with regular video cameras, there are a bunch of companies that make accessories so you can make it look like you used a power zoom, like the Nano focus+zoom lever from RedRock Micro. It’s two pieces (sold separately, of course, because this is video gear and therefore a license to print money), but luckily, neither is too expensive. First, you need the focus gear, which is sized to fit your particular zoom lens, and that runs around $45, but that’s just for focusing (very nice to have, by the way), but then you add this zoom handle to it, for another $35 or so (also worth it), so you’re into both for only around $80, but it sure makes zooming smoothly a whole lot easier.
As you’ve probably learned, many DSLR cameras don’t autofocus when you’re shooting DSLR video, so then it’s a manual thing, but that doesn’t mean you can’t use Autofocus to help you out. The trick is to use Autofocus before you start shooting, so basically, you turn on Live View mode, but don’t start recording yet—instead, aim your camera at your subject, press the shutter button down halfway to lock the focus, then move the Auto- focus switch on the barrel of your lens over to “M” (Manual) mode, and you’re all set. Now, the only downside is if your subject moves to a new location (even if it’s two feet away), you have to do this process again (luckily, it only takes a few seconds each time you do it, and you get pretty quick at it pretty quickly).