Practice Manual Focussing

Question

I'm planning on shooting a short film in about 2 weeks with my Nikon d5300. Since its aAutofocus is unusable for video (it's great for photos, but too slow to be used for video in live view), I decided to manually focus. There will be many close-up shots (i.e. the actor's face, maybe a bit of the shoulders) with a shallow depth of field (up to f/1.8, 35mm). Often, the distance to the subject will vary throughout the shot as there will be camera movement.

So I figured I need to practice manual focussing. How? Do I simply take an object, record a video, move the camera and try to keep in in focus? Do you have any other tips?

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Update

I still did not get to shoot the short film as planning didn't go as expected and then, I had a lot of stress with school. However, the answers so far are great in that they explain how MF is usually done on a higher budget. I still however miss how I can practice focussing manually.

Answer 1

Ever see the credit for "focus puller" in a film's credits? That's a single person's job, just to keep the camera focus where it should be on a moving shot (or even for changing the focus point at the right time in an otherwise static shot).

Usually the shot would be blocked out before hand, and they would work out exactly where the object of focus is going to be throughout the shot - they know in advance exactly where the focus needs to be at what time, and that person will make those focus adjustments as the shot is filmed, while other independent operators are moving, zooming, tracking, etc the camera. If your camera has the ability for the focus to be remote controlled via a pre-programmed sequence, that is also an option (usually you would remote control the camera movement as well, so it is all in sync).

Trying to manually track the focus while you're also operating the rest of the camera will be difficult to achieve accurately. I would consider breaking up your shots if possible, and cutting between more static shots. Otherwise just rehearse the shots as much as you can - it's not that it can't be done, but there's a reason films have an independent person working on just that task.

Answer 2

Don't try to judge critical focus from the viewfinder on the back of the camera. They are usually far too low resolution to be able to tell if things are pin-sharp or not (even with a loupe device). You'll need an external monitor, the higher resolution the better. You can use focus assist if your camera has it, which adds a highlight colour to sharp edges. This is useful for run-n-gun situations but again for critical focus relying on that alone will often result in disappointment.