How to Use a DSLR Zoom Lens When Filming
Personally, I'm not a huge fan of zoom lenses; I usually use prime lenses while shooting video, as they're typically faster, sharper, smaller, and lighter than any zoom lens on the market. In general, zoom lenses have more image-quality issues than prime lenses do, and they can cost excessive amounts. I've found that even the cheapest prime lens can give you a stunning image.
However, zoom lenses can be very useful and versatile, especially if you are planning to use the DSLR to take stills as well as video during an outing. (Plus, you don't have to carry around five prime lenses in your bag.)
If you're shooting video with a zoom lens, here are a few tips that should help you out.
1. Use a tripod.
By using a tripod, a monopod, or another stabilizing system, you can keep both hands free. That way you can control the zoom with one hand and the focusing with the other hand.
2. Don't zoom while you're recording.
Unless you are going for the jerky, crash zoom, don't zoom while you're filming. It's likely to distract your audience from the content of your video, and it might even nauseate them.
3. Look for a zoom lens with a constant aperture.
When you're shopping for a zoom lens to handle video, keep an eye out for a model with a fixed aperture throughout the zoom range. Most zoom lenses' aperture narrows as you near the telephoto end of the zoom range. With a fixed-aperture lens, the image doesn't get darker as you zoom in.
4. Select a zoom lens that covers a lot of bases.
I have two zoom lenses: a 17mm-45mm one and a 70mm-200mm one. All of my other lenses are primes. The reason I have those zooms is because if I am in a situation where I can't change lenses quickly (or don't know what is going to happen), I know that I can cover the subject no matter what happens and where they are.
5. Use a zoom lens only in well-lit situations.
Remember: Zoom lenses are generally slower, as they usually have narrower maximum apertures than prime lenses do. In low-light situations, a zoom lens will struggle, so it's a good idea to use a fast prime lens in darker settings.