50P/60P Shutter Angle Question

[Guest]

I have a couple of questions regarding shutter angle when using 50p (I live in PAL land but questions relevant to 60p too).

 

1. If you're going to conform 50fps to 25fps for slow motion, isn't it best to shoot at 1/50th shutter speed (360 degree) in order to retain a 180 shutter angle once the footage is conformed? I think most stuff I've read seems to suggest shooting at 100th sec in 50p even for slow mo. Why? Just to be clear I'm not talking about using twixtor etc. I'm sure this has been discussed before elsewhere, but I can't find anything clear from a quick search.

 

2. My D5300 shoots 50P at a bit rate of about 37mbps, whereas in 24P it shoots at about 23mbps. So I'm wondering - why don't I shoot 50P at a 360-degree shutter angle (50th sec) and benefit from both the high-bitrate (more detail, less macroblocking, etc) and the look of 25fps motion blur. I might be missing something about the significance/function of shutter angle here, but right now I can't think why this wouldn't work. Just to be clear, I'm not talking about conforming 50p here - this question is about real-time footage.

[Quirky]

I have a couple of questions regarding shutter angle when using 50p (I live in PAL land but questions relevant to 60p too).

 

1. If you're going to conform 50fps to 25fps for slow motion, isn't it best to shoot at 1/50th shutter speed (360 degree) in order to retain a 180 shutter angle once the footage is conformed? I think most stuff I've read seems to suggest shooting at 100th sec in 50p even for slow mo. Why? 

 

Disclaimer: I'm in no way a slo-mo expert, but I believe this one could be seen like a more generic question.

 

The way I see it, the shutter speed is relevant to the frame rate you are shooting with, and keeping the 180-degree shutter  related to the actual shooting frame rate is likely to produce more natural/pleasing looking end result, slo-mo it in post or not.

I still consider myself a mere novice or apprentice, but I'm also old school, always shooting with fixed 180 degrees (or 17x,xx) shutter related to the frame rate, like the film cameras did.

 

Regardless of the frame rate, the shorter the shutter speed, the more stroboscopic ('staccato') the movement will become, (obviously), and there will be less motion blur, too. A blurry slo-mo usually doesn't look that pleasing, but one could, and no doubt should, do one's own experiments, whenever the gear allows that.

 

My recent camera (that I've just sold) only shot with 25p but, I'd imagine using a 360-degree shutter angle related to the actual shooting frame rate might give you footage that doesn't look "quite right," even if/when you slow it down. If my next camera has 50p, I'll do my own experiments but, I doubt that using three-sixty for slo-mo will yield any better results than shooting the old-fashioned way.

[Guest]

A blurry slo-mo usually doesn't look that pleasing

 

This is a good point - also somewhat confirmed by my own experiments with 50P + 1/50thSS

[andy lee]

just a point of note ...... 50p 1920x1080 on my G6 is noisier than 25p or 24p

even though it is a higher bit rate per second

so check this on your Nikon too

 

I personally would stick with 25p 1/50 for most work , It will look cleaner

[Guest]

just a point of note ...... 50p 1920x1080 on my G6 is noisier than 25p or 24p

even though it is a higher bit rate per second

so check this on your Nikon too

 

I personally would stick with 25p 1/50 for most work , It will look cleaner

Yes I also have a G6 and have noticed this too I think (for me 24p avchd is by far the nicest codec on the G6). Thanks for pointing this out though, I'll have to do a D5300 50p/25p/24p side by side.

[Guest Ebrahim Saadawi]

1-It's due to motion blurr, slow motion looks best with a high shutter-speed, it's subjective though and yes, if you want to do it at 1/50 it's fine as long as you like it.

2-I am pretty sure I've read somewhere (Bloom's blog?) that by slowing down the footage by half, your bitrate is also effectively reduced by half.
Therefore, 37 mbps 50p when conformed down to 25p would end up more like 16-17 mbps and will make grading actually oharder than the standard 24 mbps.
Not certain though, for all I know this might be complete non-sense! :D

[dahlfors]

I have a couple of questions regarding shutter angle when using 50p (I live in PAL land but questions relevant to 60p too).

 

1. If you're going to conform 50fps to 25fps for slow motion, isn't it best to shoot at 1/50th shutter speed (360 degree) in order to retain a 180 shutter angle once the footage is conformed? I think most stuff I've read seems to suggest shooting at 100th sec in 50p even for slow mo. Why? Just to be clear I'm not talking about using twixtor etc. I'm sure this has been discussed before elsewhere, but I can't find anything clear from a quick search.

 

At least, this is how I've understood shutter angle:

 

At 1/100 shutter speed at 50 fps, it means that for the duration of each frame (1/50th of a second), the shutter was open for half of the frames duration. When you take one second of 50 fps footage and conform it to 25p slomo, you are spreading out your 50 frames for a duration of two seconds at 25 fps, that's the only thing that changes. When you step between frames, each frame will have captured half of the frames duration and motion in real time. The shutter angle remains at 180 degrees - because for each frame's duration the shutter has still been open half of the duration in real time.

If you mix slomo footage with 25p at 1/50 shutter speed (180 degree) - the same property applies here - the shutter has been open half of a frames' duration in real time. And it is this property of capturing half the motion & time of a given frame that makes 50p slomo footage at 1/100 shutter speed look the same when conformed.

 

Hope that makes sense :)

[Guest]

1-It's due to motion blurr, slow motion looks best with a high shutter-speed, it's subjective though and yes, if you want to do it at 1/50 it's fine as long as you like it.

2-I am pretty sure I've read somewhere (Bloom's blog?) that by slowing down the footage by half, your bitrate is also effectively reduced by half.
Therefore, 37 mbps 50p when conformed down to 25p would end up more like 16-17 mbps and will make grading actually oharder than the standard 24 mbps.
Not certain though, for all I know this might be complete non-sense! :D

Thanks  :)

 

1. Yes, having reviewed my test footage this is now obvious to me. I guess it's a case of finding a good balance between nice motion blur and too much staccato. 50P at 1/100th sec generally seems to look good, 50th sec too blurry.

 

2.Yes you are correct - the bitrate gets halved when conformed by 50%, but as I said in my OP my 2nd question isn't addressing conformed footage (slow mo) - I am talking about 50P played at 50fps with this second question.

[Guest]

At least, this is how I've understood shutter angle:

 

At 1/100 shutter speed at 50 fps, it means that for the duration of each frame (1/50th of a second), the shutter was open for half of the frames duration. When you take one second of 50 fps footage and conform it to 25p slomo, you are spreading out your 50 frames for a duration of two seconds at 25 fps, that's the only thing that changes. When you step between frames, each frame will have captured half of the frames duration and motion in real time. The shutter angle remains at 180 degrees - because for each frame's duration the shutter has still been open half of the duration in real time.

If you mix slomo footage with 25p at 1/50 shutter speed (180 degree) - the same property applies here - the shutter has been open half of a frames' duration in real time. And it is this property of capturing half the motion & time of a given frame that makes 50p slomo footage at 1/100 shutter speed look the same when conformed.

 

Hope that makes sense :)

 

Yes this makes perfect sense. I guess what I don't understand is why the 'gap' seems to be important - i.e. that there is a portion of time that is not captured between frames. I suppose that knowing this would also answer my 2nd question. 

 

Ultimately I suppose it's an aesthetic/subjective thing, but it would be interesting to hear a few theories about why 180 degrees looks 'right'.

[Quirky]

 there is a portion of time that is not captured between frames. I suppose that knowing this would also answer my 2nd question. 

 

Ultimately I suppose it's an aesthetic/subjective thing, but it would be interesting to hear a few theories about why 180 degrees looks 'right'.

 

As long as we're talking about traditional (analog) film, the non-exposed time between the frames is easy to explain, to block the film port and advance the next frame in place for the next exposure. The shutter and the film advancing mechanism were basically a bit like a piston, rod and the crankshaft, in lack of a better analogy right now.

That's the origins of the thing, and there is a nice explanation for the digital version of it, too, somewhere, but I don't know which words to search it for. But there is at least one very nice and visual explanation for the whole frame rate and shutter speed/angle online, and once you see it, you more or less get it right away, much better than with words only.

The portion of time not captured will have an effect on what the row of still images streamed before our eyes will look like. Apparently our brains have an internal "frame rate" as well, and apparently the sensation of smooth motion picture is a matter of both learned expectations (cinema) and our internal frame rate. I'm sure some expert in that particular field will be able to give a much better explanation, though.

[dahlfors]

On wikipedia, there is a nice animation of how the shutter worked on film cameras, which also makes it very clear why it is called a 180 degree shutter:

 

http://en.wikipedia.org/wiki/Rotary_disc_shutter

[dahlfors]

Yes this makes perfect sense. I guess what I don't understand is why the 'gap' seems to be important - i.e. that there is a portion of time that is not captured between frames. I suppose that knowing this would also answer my 2nd question. 

 

Ultimately I suppose it's an aesthetic/subjective thing, but it would be interesting to hear a few theories about why 180 degrees looks 'right'.

 

As far as I know, it's all because humans can perceive a lot more than 24 fps.

 

In computer gaming with 3D games, it isn't a fully smooth experience until you reach somewhere around 60-100 fps. In general, computer 3D games don't add any motion blurring (at least not older ones like classic Quake), so it's just a sequence of images rendered as fast as possible. It can't be really said to have a shutter speed, but let's say it has a shutter speed far exceeding what a camera would do, like 1/100000.

 

At this shutter speed most individuals perceive it as a smooth animation at somewhere around 60-100 fps, some ppl even claim to be able to spot changes in the smoothness up to 120 fps or so (true or not is debated). What we can say though, is that it doesn't look smooth or "right" for people at 24 fps, because their eyes and brains can process images much faster.

 

So at 24 fps, what makes 180 degree shutter angle better - is that it smoothens it out for our perception that exceeds the 24 fps. Yet it retains a bit of the stuttering due to the 24 fps - which is what we're used to in films (and similarily TV as well - in 25p PAL countries).

 

Personally, always seeing 25p on TV, and films in 24p, but never 30/50/60 fps material - I didn't think 24p and 50p would be that much different for me. Not until I shoot my own 50p and 60p footage and viewed it on a computer. It was then when I finally understood what people meant with 24 fps being an important part of the film look.

[fuzzynormal]

It was then when I finally understood what people meant with 24 fps being an important part of the film look.

 

Yeah, a lot of people have a hard time understanding how frame rate can make an image appear "sharper" even though an image might have the same resolution as another.  It's true though.  Get the frame rate up around the human eye speed of 60fps and the brain just sees it more "natural."  

 

However, I believe that the motion blur of 24p will be with us for generations, even though it's a goofy legacy frame rate, simply because movies are a creative art form.  Using a slow frame rate can help create the context of an alternate reality.  That's why I like it anyway.

[Sean Cunningham]

The "sharper" aspect has to do with the shutter speed, not the frame rate.  When you increase the frame rate you're also increasing the shutter speed.  Shooting with a high shutter speed at 24fps produces the same spatial crispness just without the temporal fluidity that the higher frame rate would have given it.

 

In the 48-60fps range your brain chemistry changes how it interprets visual stimulus.  At these speeds it's treating it as something happening live and now.  That doesn't mean that you consciously accept what you're seeing as real, because you don't suddenly forget you're watching a movie and sitting in a theater but your brain is interpreting the imagery as something that you're witnessing in realtime.   This can create certain involuntary reactions to what you see (good for novelty/theme park films).  All of the research into this phenomenon was done a long time ago by Douglas Trumbull.

 

As a measured scientific fact this is something that Peter Jackson needlessly screwed up on, either because he failed to research previous HFR for narrative attempts or because he failed to properly interpret the data (as well as appreciate the absolute flop that ShowScan was).  He likely thought that the very real changes in brain chemistry that happen when a viewer is stimulated this way would aid the audience's suspension of disbelief but it works in the opposite way as well.

 

HFR allows the audience to see through the veil of pseudo-realism that works for narrative films (that used to also count on the impressionistic recording of light and color by celluloid which added 50-75% more production value to what was being photographed in the case of miniatures, mattes and make-up) and perceive what's actually happening before their eyes: people playing dress-up, with heavy make-up on, carrying props that look like expensive items from a Halloween Store.  

[Guest]

This can create certain involuntary reactions to what you see (good for novelty/theme park films).  All of the research into this phenomenon was done a long time ago by Douglas Trumbull.

Very interesting, I'll have to look that up. Trumbull is awesome. I wrote a lot about his work on Blade Runner in my fine art PhD thesis a few years ago. It's great to see he's working on major features again - his stuff in Tree of Life was the best thing about that film for me. It's also great to see his aesthetic is coming back into fashion (e.g. Moon). I don't know much about VFX but surely the Dark Knight films owe something to the guy too?

 

HFR allows the audience to see through the veil of pseudo-realism that works for narrative films ... and perceive what's actually happening before their eyes: people playing dress-up, with heavy make-up on, carrying props that look like expensive items from a Halloween Store.  

 

I believe the statistics, but isn't this as much to do with a learned audience/cultural response to the 24fps aesthetic, rather than a 'natural' one? Personally I'm no fan of HFR, but when it comes to art I'm no fan of conservatism either. I believe that Jackson's attitude is that audiences can learn to suspend their disbelief for HFR just as they have with 24fps. As you say, 24p triggers a certain response in an audience that tells them "this is a film - tune into cinematic language". But this is a learned response not a biological one. I prefer the 24fps aesthetic - possibly because of all the history, possibly because it has a nice feel to it, perhaps a bit of both. Personally I wouldn't want film to change to HFR entirely. I guess I'm just questioning your opinion that Jackson is 'wrong'. I believe creative innovation requires the artist/filmmaker to be comfortable with a certain amount of 'work' and open-mindedness on the part of the audience. And I'm always a little suspicious of any immediate backlash against innovation/change (which Jackson certainly got). I think it will take time to truly judge the worth of HFR. I'm not really disputing your point - I don't know enough about this stuff to do that - just food for thought!   :)

[Sean Cunningham]

Very interesting, I'll have to look that up. Trumbull is awesome. I wrote a lot about his work on Blade Runner in my fine art PhD thesis a few years ago. It's great to see he's working on major features again - his stuff in Tree of Life was the best thing about that film for me. It's also great to see his aesthetic is coming back into fashion (e.g. Moon). I don't know much about VFX but surely the Dark Knight films owe something to the guy too?

 

Yes, he's an amazing guy.  It's too bad he went a little crazy with the whole ShowScan thing and took his toys and left when nobody wanted what he was selling.  I can only imagine how things might have turned out different by the early '90s if he was still a presence in the VFX industry because nobody else, not even ILM, did miniatures and mattes or opticals to his level.

 

As for Moon, I'm assuming you're making a reference to 2001.  Trumbull was very innovative on that film and the work stands to this day but I feel his name has mistakenly been associated with the entirety of the work and absolute responsibility.  Con Pederson was the effects supervisor for 2001 and deserves the lion's share of the credit for the work.  He was a quiet guy though and preferred to stay in the background.  He went on to co-found two award winning effects companies (Robert Abel & Associates, Metrolight Studios) as well as become one of the godfathers of computer graphics.  Not only a major influence on my getting into the industry but, as luck would have it, one of my first mentors once I'd arrived.

 

I don't know that any of the Dark Knight effects really derive directly from Trumbull.  He's one of several giants that all visual effects pay respect to.  His legacy is more one of optical quality and design.  Don't forget, the difference between how miniatures were handled between the days of 2001, where you couldn't do repeatable pass miniature photography (which dictated the style of photography and compositing used in that film), and Blade Runner, whose work depended on heavy use of repeated photography of miniatures plates, was because of John Dykstra.  

 

Trumbull's company was ultimately just better at it and so his work in the '80s stands above ILM's on the Star Wars trilogy, Indiana Jones and E.T. (among others) or that of Richard Edlund's BOSS Film (2010, Ghost Busters, etc.).  You didn't see distinct matte lines or obvious density changes or hue shifts in the optical composites of effects elements in Trumbull's company's work.  

 

He even proved to be a gifted storyteller.  Brainstorm, to this day, is one of my favorite films (scifi or otherwise), was decades ahead of its time and is often criminally overlooked because its failure at the box office is so linked to Trumbull's failure to make ShowScan "a thing".  It's too bad.

 

 

 

I believe the statistics, but isn't this as much to do with a learned audience/cultural response to the 24fps aesthetic, rather than a 'natural' one?...

 

 

No.  It's an involuntary reaction.  Trumbull (and perhaps psychologists before this, but his work on ShowScan is the most appropriate in this context) and his research measured what was going on in a person's brain under different stimulus.  That's got nothing to do with culture and everything to do with evolution.  It's getting into fight-or-flight territory.  This isn't frontal lobe stuff.

 

If it was just the temporal aesthetic then, yes, audiences could grow to at least accept HFR but the brain is processing HFR stimulus in a completely different way than "normal" film and this is wired and unavoidable.  It isn't simply an aesthetic issue and that's why Jackson was a fool.  

 

Jackson is essentially making the fat/ugly girl's argument on the subject.  Here too, science has already proven that attraction is involuntary and derived from areas of the brain beyond the bounds of our conscious control (or influence by culture).

 

 

edit: besides the temporal issue, going back to the spatial issue, it's been a known phenomenon since the birth of HDTV that techniques that used to work with old formats, be that SD analog or film, do not work with HD.  That compounds Jackson's error.   None of the craft associated with what it takes to pull off the visuals in a fantasy film are unaffected by the change.  They have not kept pace with technology, many of them.  

 

Make-up is hit the worst.  They've failed to keep up even with an audience's expectations and changes in shooting styles on film.  The shift to digital is something whole sections of the make-up effects industry may never recover from.  They need multiple quantum leaps in materials and mechanical techniques now.  The days of locked off cameras and shooting everything in the dark are long gone.

[Vesku]

When I shoot sports (GH3 1080 50P) I use shutter speed 1/160s. If I want sharper motion I shoot 1/200 os 1/250s. Then I can get good still frames and sharp slow motion.

 

I can see clearly the difference between 50P and 60P with same shutter i.e. 1/160s. 60P is more fluid to watch. I think that 70-80 FPS would be even more fluid and I could then use shorter shutter speed.

 

Sports i.e. soccer is completely unwatchable when shooted 24P with any shutter speed. I have tried 1/25s - 1/100s. It is too soft of too flickery.

[Guest]

Didn't Trumbull come up with a camera/codec/post-method or something with in-shot variable frame rate? So that action sequences could be filmed in the same shot as slower scenes ...

[Guest Ebrahim Saadawi]

2.Yes you are correct - the bitrate gets halved when conformed by 50%, but as I said in my OP my 2nd question isn't addressing conformed footage (slow mo) - I am talking about 50P played at 50fps with this second question.

Oh didn't see that (because I didn't expect you'd be willing to shoot 50p and display it in realtime, and of course because of my lazy reading techniques B) 
Apart from all the different personal (and very technical!) views about "best" framerates mentioned above, I believe that it's only you who's to decide whether it's the best, or worst, for you. 
Shoot and display at 48/50p as long as you're aware of the aesthetic difference from 24p and not just doing it for the slightly higher bitrate. 
Just don't make the decision of choosing 24p vs. 50p based on a slight difference in bitrate. The disadvantages of not choosing your preferred framerate (whether 24p or 50p) far exceed the advantages of a slight increase of bitrate.   

[Sean Cunningham]

Didn't Trumbull come up with a camera/codec/post-method or something with in-shot variable frame rate? So that action sequences could be filmed in the same shot as slower scenes ...

 

This would be the first time I've heard of this.  It still seems very special interest though with lots of sports potential.  You would of course have to light for high speed by default.  Not a big deal for sports though.