What are parfocal lenses? Are they important? And why do filmmakers want them?

The term “parfocal lens” has only really come into common usage amongst the general population over the last decade or so as our DSLRs and mirrorless cameras have allowed us to start shifting more towards shooting video content. But what exactly are they? And what’s the big deal?

As this video from Michael the Maven explains, parfocal lenses are zoom lenses, but they are zoom lenses which keep their focus distance through the entirety of their focal length range. What this means is that as you recompose for a tighter or wider shot of your subject, you don’t have to refocus the lens. It stays exactly where it was.

Most zoom lenses designed for photography are not parfocal. As you change your focal length, you need to refocus to keep that subject – a subject which hasn’t changed in distance from the camera – looking sharp. For photographers, this isn’t so much of a problem, especially with as advanced as autofocus systems have become. But for video, this can become a big issue and waste a lot of time.

When I started learning to shoot video properly, I was using Sony DSR500 broadcast cameras with parfocal lenses which were always manually focused. Mostly we were covering events with a couple of locked off DSR500s and a Sony EX1 for walking around with. One of the big advantages of using parfocal lenses on the DSR500s was that when we were setting up, we were able to zoom right into our subject at the long end of the lens’ focal range, focus on the subject big in the viewfinder, and then zoom back out to compose the scene how we wanted, knowing that our subject was still going to be in focus.

Sure, these days, you have other options. Many cameras allow you to zoom into what the sensor sees using buttons on the back of your camera. And some external monitors like the Feelworld F6 Plus (review coming soon!) allow you to pinch to zoom. But it’s not quite the same. As you zoom in, you lose detail, so you’re still only seeing a best guess at sharpness, and you could be just slightly off. Not noticeable on the camera’s LCD or even an external monitor, but noticeable in the final footage when viewed at full quality.

Aside from the lack of true focus accuracy with these methods, they’re just slow, too. Pinch to zoom and swiping on an external might feel quick compared to punching buttons on the back of the camera, but it’s quite slow compared to simply rotating a ring on a lens, especially when you’re either just about to move over to the focus ring or have already focused and are just coming away from it. Both rings are right there next to each other.

Fortunately, now that the ability to shoot good quality video has become more common and more people are starting to become aware of parfocal lenses, manufacturers have started to produce more of them. And not all of them cost crazy money, either. DZOFilm offers a couple of parfocal cinema zooms for $1,600-1,800 each.

Once you try a parfocal zoom, you’ll never want to go back to photography or non-parfocal zoom lenses if you can avoid it.

Do you use parfocal zoom lenses? Or do you just use whatever?