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0 pointsdagmx1y ago0 comments

Well that’s just down to a difference in definition and need for high frame rates.

The content is there. But the definition doesn’t match your own. Much like how many film and game results don’t match each other as well outside of just HFR .

Anything above 24/30 fps is high frame rate for film.

Frame rate for film is an aesthetic choice, and a business choice. Unlike gaming, which only conceptually uses a pinhole camera model, frame rate changes dramatically change the lighting needed, the quality of motion blur and the emotional response.

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eslaught1y ago· 4 in thread

> frame rate changes dramatically change the lighting needed

Can you explain this?

Each frame is a effectively a still taken at some shutter speed. Suppose you shoot at 1/1000 shutter speed and you're comparing 60 vs 120 FPS. In theory you get twice as many frames at 120 FPS, but every other frame should be identical to what you'd capture at 60 FPS (in a hypothetical world where you can position two cameras simultaneously in the same physical space).

I just don't get how changing FPS influences lighting unless you're making an assumption that FPS and shutter speed are entangled somehow. But I don't see how that fundamentally needs to be true except at the very slow end of shutter speeds.

dagmxOP1y ago

Frame rate and shutter speed are entangled fundamentally.

Frame rates put a cap on shutter speeds. At 24 fps, the fastest you can go is 1/24s. At 120 fps, the fastest you can go is 1/120s.

Start first with the aesthetic aspect of motion blur.

Most film is shot relative to a rotary shutter [1], with a 180 shutter being the norm, which is effectively half the frame rate. This is essential to the look of cinema today. Anything longer feels streaky and prone to feeling a bit drunk (see open shutter films by Dante Spinotti etc) and anything shorter feels like it becomes too sharp and soap opera like (see the first hobbit).

The second hobbit film went to great lengths to make the motion blur feel more like 24fps motion blur. At 48fps you have to shoot open shutter (1/48s) to match 24fps style motion blur. Any higher than 48fps and you cannot match the 24fps look.

Now this is a purely subjective choice, as is 24fps today ,given we don’t rely on optical audio track,, but it’s ingrained in people for the past 100 years. It’s the cinematic look.

Then there’s the practical aspects.

Firstly is lighting. Increasing frame rate puts a cap on shutter open time. That’s significantly more light that’s needed for every shot. This greatly increases the complexity of films where we’re already using massively high power lights. That means a ton more heat and expenditure.

Then there’s the heat of the cameras. Filming is brutal on cameras. As you increase frame rate, you increase the load significantly, leading to potentially much shorter shooting times.

Beyond that, there’s the expenditure of more frames in general. Doubling frame rates also doubles cost for storage, and the cost of post effects.

And for what benefit really? As much as I like some aspects of 48fps, audiences have pretty universally panned any shifts away from 24fps as unnatural.

[1] https://en.wikipedia.org/wiki/Rotary_disc_shutter

eslaught1y ago

Thanks for the reply. I really do appreciate it, because coming from the still photography world I've never understood this.

Not to be pendantic, but you can't you achieve motion blur by blending frames? That is, shoot at 1/240 and either average or add 10 frames together in an overlapping sequence to get 240 FPS with motion blur that looks like 24 FPS?

I'm only half convinced about lighting. Certainly, if a great deal of light is already required, then running a faster shutter speed means you need more light. That's basic physics. But I've been doing still photography indoors, with horrible lighting, and often I don't need to shoot any slower than 1/90 or so (and often can't, depending on the lens I'm using, since I shoot handheld). Maybe I'm using a larger aperture? Not sure what gives because with modern digital camera bodies, sensors have gotten really, really good.

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zestyping1y ago

Did you mean, at 24 fps the _slowest_ you can go is 1/24 s, and at 120 fps, the _slowest_ you can go is 1/120 s?

SSLy1y ago

HFR sequences in avatar2 were weird at first, but after 10-15 minutes became wonderful and caused the 24 FPS ones to feel jarring.

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