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Comment by KineticLensman | Hacker News Reader

Yes. It’s very rare to see the focus change during a movie or TV show. The main exception is when the focus switches between two people talking, when their positions are known in advance and dialled in so there isn’t any visible hunting

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You can actually see focus changes quite often in movies and TV shows - but they're usually done intentionally to accentuate something, e.g. a focus pull from a foreground object to an actor in the background.

But it's a slow and smooth motion without any focus breathing intended to highlight an object or an actor, not just autofocus hunting to find something

This is probably an elementary question, but are those focal shifts still done manually, with a camera guy turning the ring by hand? Or do they set the two points in advance and hit a button to start a motorized transition?

there's a dedicated person usually called a focus puller.

Kind of both? You've usually got a small motor connected to the lens that turns the focus ring.

A dedicated person, called a focus puller, has a remote with a wheel on the side. By turning this wheel the focus puller can remotely control the focus ring of the lens.

The remote usually allows the focus puller to set the maximum range of motion with A/B points. The system doesn't automatically execute the focus pull, but with the hard stops at the A/B points the focus puller can make sure they don't overshoot the target.

At that point it sounds easier to have the focus switch executed automatically with all relevant parameters preset, e.g. duration or curve. Sort of like CSS transition or MIDI automation.

look at this video: https://www.youtube.com/watch?v=6AsGgR9oZak

Back then the focus puller would use a remote connected by a cable, which is why you see a focus puller running behind the steadicam op in that video.

That's why while you've got A/B points set and marks set on the focus control, you still need a human.

Behind the scenes, look for when they are "marking," which is leaving little piece of tape or otherwise on the ground where the actors are standing. The focus puller will make indications on their focus ring to match these; as long as the actor "hits their mark" the focus will be dead on. A majority of time the operation is fully manual (though possibly remote to the camera)

That's how I remembered it too. And that's also then one of the major differences between this app and an actual professional camera - because on a smartphone you only have autofocus. Which works most of the time, but I've had some recordings of concerts with weird lighting, smoke and other stuff which were out of focus for quite a few seconds. One of the most stupid things is when you try to take a picture of a bird or airplane in flight and your smartphone can't focus on it because it's too small. Why can't it just default to focus to infinity if it can't find anything to focus on?

>because on a smartphone you only have autofocus

Focus can be controlled manually on the iPhone (in 3rd party apps).

Focus pullers at work in case anyone is interested:

https://yewtu.be/watch?v=5cfTuy6lNaM

https://yewtu.be/watch?v=ZlEp_s8yHYA

Having worked as a loader/2nd AC and getting thrown into the focus puller chair on some b-roll - focus is changing constantly. On a movie set, it’s pretty much an entire person’s job.

Does the focus change during a shot?

Unless the distance of the camera and the subject do not move at all, the focus will be actively changing - yes.

Depending on various conditions (lighting, lens choice, etc) there might be a very large distance range that is in focus - or it might just be a few inches. Even if the focus puller isn’t doing any big focus swings, they are likely making small adjustments.

It's not rare at all. It is just deliberate in movies/shows, not something algorithm on camera constantly fiddles with.

With “Cinematic” video mode on the iPhone you can edit focus in post with the iPhone Photos app. It does a good job for this two person talking scenario.

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