48p or 24p?

[SPZ]

Here's a question that's been troubling me for a while. I've heard cinemas project film at 48fps. SO wouldn't it be wiser to shoot Film projects in 48p, compared to shooting 25p or 24p?

 

[Andreas]

I don't think that with film is the case, but the new digital cinemas will project 24 and 48 for sure. So yes, the same question troubles me also. And I add one more question: shooting PAL, is the transition from 50p to 48p smooth or not. Is there problems wih sound synchronization ?

 

[scharky]

Projectors often display 48fps, however the footage shown is 24fps. Each frame is shown twice in order to display more smoothly. Many digital projectors use the same technique, so shooting 48fps would in effect give you footage that would play back at 50% real time.

 

[smelni]

Its related to how we perceive motion - our eye requires 24 images per second to perceive motion properly - but 24 frames would introduce a flicker effect. To remove the flicker effect each image is shown twice to result in 48 frames per second.

 

[Barry_Green]

Cinemas do NOT run at 48fps. The film runs through the projector at 24fps. Think about it -- if it ran through at 48fps, your 90 minute movie would be done projecting after just 45 minutes.

The cinema shutter flashes the frame twice, like scharky said. That means you will see one 24 frames per second, but each frame will be flashed on the screen twice to try to smooth out the flicker that comes from shutting the shutter entirely as the film is advanced to the next frame.

But you will only see 24 distinct changed frames per second.

 

[pheboglobi]

Its related to how we perceive motion - our eye requires 24 images per second to perceive motion properly - but 24 frames would introduce a flicker effect. To remove the flicker effect each image is shown twice to result in 48 frames per second.

They actually used to run film @ 16-20fps in camera prior to the advent of sound, which is what required the 24fps rate for the sound to run properly (since it was on the film itself). 16fps is pretty much the lowest limit for humans to perceive as continual motion. And for a long time, the standard rate for 8mm and Super8 (w/o sound) was 18fps.

I was under the impression that most modern projectors have 3 blades built into them, so they display 24fps films at 72Hz. That way it removes the slight flicker that occurs at 48Hz and it lets slightly more light pass through and it'll appear brighter. (There are even a few 5-bladed projectors floating around, and 16mm and 8mm projectors with 5 blades are often hot items on eBay.)

A fun trick to do is to turn your head so you are looking at a screen with your peripheral vision, and since your periphery vision is better at detecting motion than the center, you can often see the flicker if the flash rate is low enough.

Garrett

 

[SPZ]

They actually used to run film @ 16-20fps in camera prior to the advent of sound, which is what required the 24fps rate for the sound to run properly (since it was on the film itself). 16fps is pretty much the lowest limit for humans to perceive as continual motion. And for a long time, the standard rate for 8mm and Super8 (w/o sound) was 18fps.

I was under the impression that most modern projectors have 3 blades built into them, so they display 24fps films at 72Hz. That way it removes the slight flicker that occurs at 48Hz and it lets slightly more light pass through and it'll appear brighter. (There are even a few 5-bladed projectors floating around, and 16mm and 8mm projectors with 5 blades are often hot items on eBay.)

A fun trick to do is to turn your head so you are looking at a screen with your peripheral vision, and since your periphery vision is better at detecting motion than the center, you can often see the flicker if the flash rate is low enough.

Garrett

Garret, that means that an Image recorded at 50hzs could probably give the viewer a more "flickery"image than one recorded at 60hz, couldn't it?

 

[pheboglobi]

Garret, that means that an Image recorded at 50hzs could probably give the viewer a more "flickery"image than one recorded at 60hz, couldn't it?

Footage shot at 60fps will appear smoother than footage shot at 50fps for playback at their respective rates, that is true. However, any display systems higher than 60fps (i.e. 70fps) will not appear any smoother than 60fps to most people. 60fps is the upper limit for the most part to humans' perception of motion.

I just wanted to make a note of my post above too - I was using the Hz to describe the display rate rather than the frame rate. Even though film is shot at 24fps, it is displayed at 48Hz or 72Hz or... whatever by basically multiplying the frames. Even though 24fps is more than enough for the illusion of continual motion, it would be too slow a rate to show anyone without giving them a headache. A light flashing at 48Hz is about the threshold for a vast majority of people to perceive as the light always being on, so that is why each frame is flashed 2 or 3 times before moving onto the next frame.

Reading back on all this, I don't think I explained it very well... sorry

Here some Wikipedia articles:
http://en.wikipedia.org/wiki/Flicker_fusion_threshold
http://en.wikipedia.org/wiki/Movie_projector

Garrett