Trying to get a good close-up by using the zoom lens is difficult because a long lens inherently has a shallow depth-of-field. This makes it hard to keep anything in focus. Plus, if the camera can not easily distinguish what to focus on, it’ll go bonkers and drift in and out, which can totally ruin your video.
Another things that makes zooming in for close-ups a bad idea is that on a zoomed-in telephoto setting, camera shake appears magnified, giving what we snobby pros sarcastically call earthquake video, spastic-cam and puke-inducing effects. A zoomed in shot can look so shaky you have to judge it on the Richter scale!
So…sorry to be the one to break it to you, but your zoom lens is of minimal use. That’s not to say that a good, locked-down-on-the-tripod-zoomed-in shot CAN’T look great, it’s just not as easy as it looks.
To make your zoomed-in shots look professional, you HAVE to use a tripod, (or something as a substitute). Even on a tripod, camera shake often ruins a fully zoomed-in shot, so lock your tripod down tightly and pray the wind doesn’t blow. The longer your zoom, the shakier it’ll look and the harder it will be to focus.
An auto-focus lens on full zoom can have an impossible time trying to figure out what to focus on if there are multiple possibilities in your shot. To avoid that problem, make sure nothing in the foreground or background is close enough to the middle of the frame so as to confuse your camera.
A professional-looking zoom will be slow, steady and smooth. Novices tend to move the camera a lot and zoom in on everything just as fast as the lens will go. Doing so will mark you as an amateur quicker than anything else. Slow down and let the auto zoom glide smoothly to a logical resting place. In other words, when your zoom is finished, the shot should be nicely framed up and not just be the middle of whatever it is you’re zooming in on.
Constantly zooming in and out is BAD TECHNIQUE. There’s really no argument about it, but novices tend to argue anyway. Generally speaking, it’s much better to cut from a wide shot to a close-up than to zoom in. Watch TV if you don’t believe me. You will NEVER see a ton of zooms in a professional done TV show.