What's a Parfocal Lens and Why Is It so Important?

If you have ever looked at the price of cinema lenses, your eyes probably watered a bit at their seemingly stratospheric cost. There are lots of reasons for those high prices, one of the most common being that they are parfocal. This interesting video explains what it means for a lens to be parfocal and why it is so desirable among filmmakers. 

Coming to you from Michael the Maven, this great video details what a parfocal lens is and why it is so useful for videographers. The majority of zoom lenses are varifocal lenses. This means that they are lenses in which the focus changes as the focal length changes. On the other hand, parfocal lenses do not change focus as the lens' focal length is changed. This offers several advantages. For example, this allows one to zoom in to focus, then zoom back out to compose an image. This is sort of operation is crucial for camera operators, for whom reasonably maintaining focus manually while zooming at the same time would be very difficult. Photographers almost never need this kind of functionality, so manufacturers make varifocal lenses, which are far cheaper. Check out the video above for more on the topic. 

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8 Comments

The last varifocal lens for an SLR I saw was in the early 1980's. I have personally never owned one. Every zoom I have used in photography has been parfocal.

Same for every video zoom lens I have ever used.

Been doing photography since 1981. Did video from about 1985 to about 1997.

Martin Del Vecchio's picture

What photo lens have you used that is parfocal?

None of the photo zoom lenses I have ever owned is parfocal. Here is a list:
- Canon 24-105mm
- Canon 24-70mm
- Canon 16-35mm II
- Canon 16-35mm III
- Canon 70-200mm II
- Canon 70-200mm III
- Canon 100-400mm II
- Panasonic 12-35mm
- Sony 24-70mm GM
- Sony 70-200mm GM

Every Pentax zoom lens I have ever purchased, stating from the mid eighties. It was about the mid-eighties that lens makers stated advertising their zooms as such, so that one can do precisely what this article says; zoom in, (with the zoom ring), focus with the focus ring, zoom out.

Many third party manufactures also used to advertise this. I assumed they stooped advertising as such when it became common-place. I am surprised by the long list of Canon & Sony lenses you have there. (Extremely surprised by Panasonic, since video is their forte). The one varifocal I have ever seen, was a Vivitar K-mount zoom which had one ring for zoom (slide) and focus (turn).

Pentax actually still features on their website the fact that they have multi-group movement internally so as to keep precise focus as they zoom.

Lee Christiansen's picture

I'm at a loss, as with others... Which stills lenses have you used that are parfocal. I don't know of any, pre or post digital... (Certainly not lots of zooms).

Starting in the mid-eighties, it was the thing to get. See my reply to Martin, above.

Good clip. “Parfocal” is appreciated in astrophotography and helps drive costs & better captures. Even the better oculars for visual observation benefit from this design feature.

Kirk Darling's picture

Parfocal lenses were a holy grail prior to autofocusing, when the typical method of getting sharp manual focus was to zoom in, focus, and zoom back out to shoot.

I had only one zoom back then, the Canon FD 80-200L. It was parfocal. Most zooms were not.

With the advent of autofocusing, the technique of zooming in to focus was overcome by the technology, so manufacturers could safely give up parfocal designs. It was autofocusing that changed the picture (so to speak).

Since I've gotten into video, I agree that it's time for parfocal lenses to come back.