Why does fps affect movies?

Question

I’m a big movie fan, but I’ve always been curious about why some movies are shot in different frame rates. I’ve heard that 48 fps is a “sweet spot” between sharoness and smoothness, and that it has something to do with shutter speed allowing more light per frame. Can someone explain this?

What are the benefits of shooting a movie in 24, 30, 48, or 60 fps? How does it affect the look and feel of the movie? And why do some movies choose to use a different frame rate than others?

Thanks for your help in advance!

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Answer 1

Almost all movies are shot at 24 fps. Essentially that was about the minimum rate that worked well enough when the technology was new and expensive. Projection at only 24 fps creates too much flicker so the standard trick is to simply show each frame twice at 48 fps. I believe some modern digital projectors even show each frame three times at 72 fps.

It turns out that people have become unconsciously conditioned to associate this 24/48 filming and projection system with quality movies. When *The Hobbit* experimented with actually filming at 48 fps people didn’t like the more realistic look (probably coupled with the excessive CGI in the action sequences). Some call it the “soap opera effect” because 60 fps TV has had this look for decades and the low artistic quality of TV content has become associated with high frame rates.

Modern technology makes films at 48 fps (and beyond) possible with some additional cost, mostly because it’s non-standard. But after the bad reactions to *The Hobbit* I don’t think a major film tried it again until *Gemini Man* in 2019 and now the latest *Avatar*. In those cases it seems the directors wanted a different, more realistic look.

One thing to note is that the shutter speed is typically half the duration of the frame rate, so a 24 fps film often has a 1/48th of a second shutter speed. That’s quite slow and allows moving objects to appear blurry. Shooting at 48 fps would suggest a 1/96th of a second shutter speed with less motion blur. If you have a short shutter speed with a low frame rate the result is choppy motion, as with a strobe light. Higher frame rates allow less motion blur without the choppy look.