Does the shutter angle remain at 180 regardless of FPS to maintain the filmic motion blur?

[Berry Spinx]

12 fps: make song last 1.956x longer by stretching it to 51.1% speed
18 fps: make song last 1.333x longer by stretching it to 75.0% speed
20 fps: make song last 1.226x longer by stretching it to 81.6% speed
22 fps: make song last 1.067x longer by stretching it to 93.7% speed
26 fps: make song last 0.907x as long as normal; play it at 110.25% speed
30 fps: make song last 0.800x as long as normal; play it at 125% speed
32 fps: make song last 0.747x as long as normal; play it at 133.87% speed
36 fps: make song last 0.672x as long as normal; play it at 148.81% speed
48 fps: make song last 0.498x as long as normal; play it at 200.80% speed
60 fps: make song last 0.400x as long as normal; play it at 250.00% speed

If the plan is to bring it back to 24fps in post, should the shutter angle be at 180 when shooting?

[Max Field]

It really depends on the look you're going for, but when shooting something with the intention of slowmo playback you generally want to crank the shutter speed to a smaller proportional fraction. Frame rate plugging into the equation of shutter angle could possibly keep the angle 180 for all of these but another thing that affects where you want to put it is how rapid the motion in front of the camera is.

Power grid could also affect light flicker if the shutter speed isn't proportional to the frequency.

[David Mullen ASC]

In general, traditional film-shot slow-motion footage has kept to a 144-to-200-ish degree shutter angle range. However, some sports commercials have been shot both with a high frame rate and a shortened shutter angle (like 45 degrees) to get extremely crisp, staccato motion. Mostly shot in sunlight...

Usually this question appears because someone wants to compensate for the light loss of faster frame rates by increasing the shutter time, but there is no free lunch, the motion gets more blurry and smeary when you go much higher than 200-240 degrees.

 

[David Mullen ASC]

I see your question though isn't about shooting for a slow-motion effect?  If you want to take 48 fps footage and convert it to 24 fps, then technically you'd want to shoot the 48 fps footage with a 360 degree shutter so that the per-frame motion blur comes from a 1/48th shutter time (which is what you'd get if you shot 24 fps with a 180 degree shutter angle.)

However there are software tricks that essentially could take 48 fps shot with a 180 degree shutter angle and blend every two frames rather than drop every other frame and thus create the blur of 24 fps shot with 1/48th rather than 1/96th. 

But then, why would you shoot at 48 fps only to convert it to 24 fps for normal motion, not slow motion?

[Saikat Chattopadhyay]

I am not sure about my answer ,correct me please if I am wrong .

In any NLE (Non Linear Editing Software),shutter speed/angle or the FPS doesn't change when you change the clip speed it will just duplicate frames (when slowing down) or blend/drop frames (when speeding up). FPS will only change when you change it manually (by re-interpreting the clip in media bin) and in that case it will adjust the duration of the clip automatically. However, if you place a high frame rate file onto a low frame rate timeline then the software will use something like "frame blending" to keep most of the data .

N.B : I have only worked on Premier,Ae and Resolve and never worked on any film-scanned footage. 

Edited August 29, 2020 by Saikat Chattopadhyay
Typo

[Robin R Probyn]

I think the simple answer is yes.. 180 degree shutter was a necessity of film cameras to move the film through the gate . 24fps. .  this "look" created by that level of motion blur became the accepted "look " of movies ..  TV electronic camera were interlaced, so a whole different look completely .. so the holy grail for digital camera became getting as close to the film look as possible..  which they could when progressive scan took over from interlaced ..   if I shoot slo mo  I try to make the shutter 180.. or close enough or depending on flicker concerns..  also good for ramping .. going from normal speed to slo mo .. used to be very popular !..

A good example is the disaster that was the 48fps Hobit version..  to the masses it looked like cheap day time tv.. as thats what everyone associated that motion blur look , or lack there of .. and the opposite was the year they shot the live MTV awards in 24fps.. alot of calls to the tv station by people claiming its wasn't a live broadcast .. because it didn't look all the live TV they had seen before ..  it may die out in time as accepted norms change .. alot of young people playing video games at much higher frame rates and they might not care about the film look in 20 years time ..

[Berry Spinx]

On 8/29/2020 at 5:26 PM, David Mullen ASC said:

I see your question though isn't about shooting for a slow-motion effect?  If you want to take 48 fps footage and convert it to 24 fps, then technically you'd want to shoot the 48 fps footage with a 360 degree shutter so that the per-frame motion blur comes from a 1/48th shutter time (which is what you'd get if you shot 24 fps with a 180 degree shutter angle.)

However there are software tricks that essentially could take 48 fps shot with a 180 degree shutter angle and blend every two frames rather than drop every other frame and thus create the blur of 24 fps shot with 1/48th rather than 1/96th. 

But then, why would you shoot at 48 fps only to convert it to 24 fps for normal motion, not slow motion?

Hi David,

I would be shooting 26-50fps to achieve slow motion. I think I meant to say: to shoot 26-50fps and place onto a 24fps timeline to achieve slow motion. 

If 144-to-200-ish degree shutter angle is recommended to maintain the filmic look blur is there a guideline on which shutter angle to choose when choosing an fps? My intended fps range is 26-48fps ish.

[David Mullen ASC]

Just stick to 180 degrees unless you have a reason to change it. You may want to avoid using lights with a AC pulse to them (gas discharge lamps and industrial fluorescents) because otherwise you'll have to keep calculating whatever shutter angle gives you 1/60th for 60 Hz or 1/50th for 50 Hz at your chosen frame rate (technically you'd use 144 for 60 Hz at 24 fps and 172.8 for 50 Hz at 24 fps.)

[Alissa Alexina]

I came to the conclusion that the most important factor in choosing a shutter angle for slow motion is how fast the object moves. Generally, fast-moving objects create that epic otherworldly look in slow motion. For subtle slow motion like walking people, 150-180 degree shutter can be fine. But a fast movement of a falling or flying object requires a faster shutter speed to avoid blurring (unless intended).

I remember editing a music video 10 years ago, with the director running around upset that the falling dice scene looked completely smeared and suspecting me of messing with the footage in post - it turned out the scene was shot at 1/50 shutter speed. I do not know the math to calculate it in advance, it is probably too complicated, but think it requires trial and error anyway. So I always use 45-90 degree shutter when things as falling, flying, being broken, thrown down or into water.

The falling coins below (90 shutter angle, 200fps) still show a fair amount of motion blur, just because the movement is so fast.

[Satsuki Murashige]

Hi Alissa, I think you are right. One well-regarded Phantom Tech that I used to work with would often recommend cutting the shutter for super slow-mo shots to ensure no motion blur.

When shooting extremely high frame rates, objects in frame move so slowly that the eye has time to scan the entire frame at its leisure. In that case, motion blur (much like missed focus, oy!) will become extremely noticeable and potentially distracting). Best to err on the side of sharpness and add the blur back in later if so desired.