Zoom lens

One lens instead of three, which is why a zoom is the sensible first purchase for anybody filming alone. The trade is optical. At a given price a zoom is slower and softer than a prime covering one of the same focal lengths, and many lose maximum aperture as you extend.

Parfocal behaviour is what catches video shooters. Most stills zooms are varifocal, meaning focus shifts as focal length changes, so zooming during a take pulls the image soft. Lenses built for cine work hold focus through the range and cost several times as much.