How do cinematographers focus on an object and blur the background?

[acearchie]

I meant it more as a gist. The focus puller will hopefully stay, why complicate things? Though if the technology matures, maybe the viewer can pull the focus, if the audience is still there for longer films.

Interesting concept. I can see it working as a more online/interactive tool for interesting ad campaigns involving more interactivity with the user as they will have to search the photo/scene for the item in focus.

It makes me a little sad that something I have worked and practiced, in my case pulling focus, has started to be corrected by a machine! Hopefully human operation will continue as I enjoy it!

 

[Mediaformae]

Altogether

The size of the sensor does NOT affect the depth of field.

It crops the image. That's all.

So to compensate for this cropping effect you, for example, use a 20mm lens instead of a 40mm lens. Using the shorter-focal-length lens at the same subject-object distance is what will affect your depth of field.

Putting it simple: The bigger the focal length, the shallower the Depth of Field.
Of course, repositioning and reframing are required.

Like some have already said, sensor size does matter.

Also, the combination between focal length, diafragm aperture, sensor size, shutter (increased shutter speed implies increased aperture, wich implies shallower depth of fileld. Hence the "blured" actualy out of focus background behind the focused subject), ND filters (less light reaching the lens implies increased aperture) and also focus distance (the smaller, the smaller depth of field; macro lenses are the perfect example for this) will altogether, directly or not, affect the depth of field.

 

[Fandongo]

Anyway, back to the thread: Focus pullers will be a thing of the past with this.

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Facial recognition is ancient technology.
The Magic Lantern hack (t2i) had an experimental constant AF feature. Largely useless, if tracking in/out it'll always be behind, but it showcases the limitless potential of DSLRs for filmmaking. Sure, AF will never (it will) be perfect, but if you're stopped down, you can use the "F--it, close enough" pulling theory.

Gimbal systems can't be touched, so it's wireless Follow Focus. Red Rock's looks awesome. It looked awesome two years ago when it won awards.

It would look even more awesome if it existed.

It'll be obsolete before it comes out if we ever get stutter-free AF-drive control.

We won't.