Relationship Between Frame Rate & Shutter Angle

[manigandan srinivasan]

Hi i have few doubts about the intermittent mechanism in a motion picture camera.

I know rotary disc is connected to frame. So when the motor runs on 1 side the Pull down claw & Registration Pin will advance frames for exposure and other side of this mechanism will be connected to rotary disk. Now the speed of this motor is based on frame rate per second (ie)24fps & 48fps will not have same motor speed. which means other side (disc side) will also rotate fast when shot is 48fps. so the exposure time for each frame in 24fps is 1/48,exposure time for each frame in 48fps is 1/96. 15 types of Shutter angles possible in camera from 11°-220°. 220° in 24fps will have 1/40 shutter speed per frame.And,220°s.a is only in panaflex camera not in arri camera.

 

Now My Question is

If i want to create a motion blur in a shot (ie) an effect created by using a slow shutter speed. What can i do if 1/40(220° S.A) Is not enough ?

Can it be created while shooting or only in post production we can achieve this Motion Blur ???

 

This is my doubt kindly clear this am very confused & if whatever i understood is wrong pls correct me

[David Mullen ASC]

If you can't increase the exposure time by shooting at a lower frame rate then you have to try a post effect.

[John Sprung]

For really long motion blur, consider digital instead of film. You can get very close to a 360 degree shutter angle. Creating more blur in post is very easy if you start with the 360 degree shutter, you just combine successive frames to make 720 degrees, 1080 degrees, etc. To make more motion blur in post with anything less than 360 to start with is much more difficult, because you have to fake the missing information. Arri's Relativity software can do it, but it's an expensive post house job. FotoKem in Burbank has it.

 

 

 

-- J.S.

[manigandan srinivasan]

thanks for the replies

i have a question

in film wont it be a motion blur if i shoot in 3 fps ??? ofcourse it will be fast motion but wont be there motion blur in it ???????

[Chris Millar]

For really long motion blur, consider digital instead of film. You can get very close to a 360 degree shutter angle. Creating more blur in post is very easy if you start with the 360 degree shutter, you just combine successive frames to make 720 degrees, 1080 degrees, etc. To make more motion blur in post with anything less than 360 to start with is much more difficult, because you have to fake the missing information. Arri's Relativity software can do it, but it's an expensive post house job. FotoKem in Burbank has it.

 

 

 

-- J.S.

 

...and do it at a really fast frame rate for more temporal resolution control ;) - the higher the frame rate the more you're tending towards complete control after the fact.

 

Of course, you'll have to code/script/fiddle lots in post.

 

Pretty sure it's the usual suspects turning up here and saying the same things we've said in the past when others have asked the same question :lol:

[John Sprung]

Yes, if you use a reasonable shutter angle, near 180 degrees, 3 fps will give you lots of motion blur.

 

 

-- J.S.

[manigandan srinivasan]

But in normal motion , a motion blur can be achieved only in post production :)

Thanks for this input i was thinking about this for last couple of days now its clear thank u sir :)

[David Mullen ASC]

With a 360 degree shutter angle, you can get twice as much motion blur at the same frame rate as with a 180 degree shutter angle, but only a digital camera can shoot with a 360 degree shutter angle.

[manigandan srinivasan]

if we shoot in 360 Shutter angle, how can there be exposure. a disc is 360 degree right ???

i have a canon eos 550d Digital camera

I shot a short film with it. I dint see shutter movement at all while i was recording a shot.

Can you explain me how it works that way in a digital camera sir ???? is it like this in arri alexa & red one also ????

[Chris Millar]

360deg means no shutter - not complete shutter

 

This would be impossible with a traditional film pull down system as it it would infer a faster than light speed pull down, you might tear sprockets or a hole in the space-time knickers doing that ;)

 

(you could achieve a cheat version with a beam splitters and two magazine system if you really wanted to though)

 

Not sure exactly how a digital system does it - but if they have a rolling shutter feed my guess is that the sensor pixel currently feeding the current frames data simply takes a frames worth of time to do its full sweep of the frame, which means that the time it takes to go from pixel to pixel is exactly the same as the time it takes to go from the last pixel of frame x to the first of frame x+1 ...

 

That's pretty much the worst rolling shutter artifact inducing scenario there is (hello iPhone and low light recording!).

 

I suppose you could have twice the resolution and do it CCD style, record a frames worth all at once with one 'half' of the pixels (call them odd), spend a frame dumping all that info while the other half of evens is charging/recording and so on...

 

You might get alternating moire issues frame to frame, which would mean having to blur it, which effectively reduces your res below the half of the original double resolution.

 

hmmm, no idea :lol: interesting stuff though

[David Mullen ASC]

Generally with a Canon, you'd set the shutter time, so usually at 24P, you'd use something near 1/48 (like 1/50) for a 180 degree shutter angle look, but you should be able to select something closer to 1/24 for a 360 degree shutter angle look, i.e. no shutter closure at all.

 

As Chris says, film needs a period for the shutter to be closed so that it can advance the film to the next frame.

 

The shutter is electronic, not physical, when shooting video on the Canon, or on most digital cameras, with a few exceptions. There is no "shutter angle" per se, that's just a naming convention, what you are actually controlling is the exposure time.

[Arun Kumar Pandey]

I dont know if this would help, but the third episode of Zacuto Shootout 2011 sheds light on various artifacts related with shutter among various cameras including RED, ALEXA, F35, CANON variants and WEISSCAM. Have a look its pretty interesting.

[manigandan srinivasan]

@David Mullen

Sir, i dint understand the last part, i am bit confused with this. in my camera while i shoot in still picture mode. i know the focla plane shutter opens and closes according to the speed i set. But, the same camera when i change to video mode and shoot a video. What kind of change it undergoes to shoot a video ??? if there is no shutter angle at all, how can a focal plane shutter designed for stills can work for a video ???

This is very confusing to me

Kindly help me with an answer or Provide a link.

 

Thanks in advance sir :)

[Adrian Sierkowski]

The Shutter (mirror) is left open in video mode on the Canon cameras and what the "Speed" refers to is how long to "Read" the sensor for.

[manigandan srinivasan]

"The Shutter (mirror) is left open in video mode on the Canon cameras and what the "Speed" refers to is how long to "Read" the sensor for."

 

 

 

Sir,in that case how do i see whats been recorded through lcd? if shutter is open means exposure is happening what gives feed to lcd ??

and is this the same mechanism for red,alexa also ?

& if the speed refers to "HOW LONG SENSOR READS" Means will there be the natural effects by shutter like blur or crisp images are possible cos i dint see any difference in shooting 1/50 shutter speed & 1/200 shutter speed with my camera ?

[Chris Millar]

Sir,in that case how do i see whats been recorded through lcd? if shutter is open means exposure is happening what gives feed to lcd ??

and is this the same mechanism for red,alexa also ?

& if the speed refers to "HOW LONG SENSOR READS" Means will there be the natural effects by shutter like blur or crisp images are possible cos i dint see any difference in shooting 1/50 shutter speed & 1/200 shutter speed with my camera ?

 

As I understand it a CMOS sensor reads info for one pixel at a time - while it is doing so the rest are doing what it takes for them to be ready the next time its their turn to dump their charge. They scan from top to bottom left to right (or is it bottom to top right to left ? :lol: or the other two options...)

 

Your LCD is just representing this feed - not sure what the issue is there ? you just present the info received yeh ? maybe worst case it might be a frame and a bit behind reality (?).

 

Sure is hard to answer questions that can get as complex as you choose...

[John Sprung]

? maybe worst case it might be a frame and a bit behind reality (?).

 

Actually, they can be several frames behind, like 6-8 in some cameras. No problem on lockoff shots, but it can look like the operator was stoned if there's any action.

 

 

 

 

-- J.S.

[Chris Millar]

It's fun playing with feedback in live to screen situations ... open aperture, close aperture, zoom, zoom - watching the blue blobs blob and pulse/strobe around (indicating a colder screen than the original signal feeding it and the delay you're talking about)

 

But I always thought the majority of delay was downstream in the video switch/mixing gear. 6-8 frames from sensor to LCD ! ouch.

 

I never noticed it with my old EX1, maybe a smidge on the miniDV cam I use as a video tap on my 16mm's.

Edited October 17, 2011 by Chris Millar

[manigandan srinivasan]

Thanks for the answers. It helped me a lot to understand the shutter mechanism and its uses better :)