Shutter Speed in Knowing

[ninjaleprechaun]

By chance did anyone on the forum work on this film? In all my Red shoots I have yet to achieve the film-like motion blur that the trailer for Knowing has down solid. Every test and shoot I've worked on has produced a nice image when relatively still, but with an overly stroby look to it upon motion (not just panning, but actor's movement, and not just your general 24p strobe).

If anyone knows, or has advice on how they have gotten a similar result, input would be much appreciated.

[Jonathan Stevenson]

1/48th shutter?

[J. Eric Camp]

I worked on the 2nd unit. Ryan Kunklemen did the principal photography. However, the work I was a part of was meant to cut into the existing scenes and as such it was a 180 shutter. Plane and simple.

It sounds to me like you have issues between your shooting fps, choice of shutter, output method and frame rate. Doing any pull down? Taking a feed off the camera's output? Only working with the proxies and rendering from there?

[ninjaleprechaun]

I worked on the 2nd unit. Ryan Kunklemen did the principal photography. However, the work I was a part of was meant to cut into the existing scenes and as such it was a 180 shutter. Plane and simple.

It sounds to me like you have issues between your shooting fps, choice of shutter, output method and frame rate. Doing any pull down? Taking a feed off the camera's output? Only working with the proxies and rendering from there?

No pulldown. I generally have done a one light in redcine then kicked out a Prores HQ file to edit with. Last two projects I've done with log and transfer and finished in Color. Would outputting to some sort of still sequence affect the way the image is processed as opposed to a quicktime output?

[J. Eric Camp]

What's your shooting frame rate. And what frame rate are your Prores's

[Chris Swinbanks]

By chance did anyone on the forum work on this film? In all my Red shoots I have yet to achieve the film-like motion blur that the trailer for Knowing has down solid. Simon Duggan was DOP.
A couple of r3d's I can still find online for vfx shots indicate 23.976fps, shutter 172 deg (1/50th). I think that's indicative of the film in general.
Chris

[josemnorton]

Is there any reason you would shoot at 1/50th while shooting 23,98?
As opposed to 1/48th?

This is exciting stuff! The RED has been here for more than a year and yet all this stuff is new.

Thanks!

[Tom Gleeson]

Is there any reason you would shoot at 1/50th while shooting 23,98?
As opposed to 1/48th?

Thats simple. In Australia where the film was shot we have an AC line frequency of 50HZ so a shutter speed of 1/50th prevents any flicker from practical fluoros or HMI that are not flicker free. If you were shooting on film you would do the same with a 172.5 degree shutter. I have shot both 1/48th and 1/50th shutter and can see no visual difference between them.

Tom Gleeson

[cinemano]

can anyone explain to me shutter angles degrees thing like im a 5 year old? : ) Id really like to know in which situations id want that... What will low number shutter angle do in comparison to high number shutter angle? i apreciate it..

[Nate Clapp]

Shutter angle can be represented by a fraction (1/48) or by an angle (180 degrees) and your preference is determined by your background. People from a motion picture background like it represented in degrees. Motion picture cameras have a spinning shutter that alternately lets light hit the film or block it (thus allowing camera to move film to next frame w/out blurring it) so a 180 degree shutter, lets you have light hitting the film half the time. At 24fps, if shutter was 360 (mechanically impossible, but anyway) your exposure per frame would be 1/24, and a 180 shutter, your exposure would be 1/48 (half of 1/24)
If you come from stills or video, you are more familiar with the fractional representation. the default for 24fps is 1/48. If you were to halve that again- 1/96 (90 degrees for the motion picture guys) you are letting the film/sensor "see" for a shorter moment in time. It will need twice as much light since you halved the time. Usually done with iris. another side effect is the shorter the exposure time, the less an object has a chance to move while it is being exposed.
this results in things that otherwise might be blurry in an individual frame ending up sharp. In "Saving Private Ryan" shutter angles of 45 degrees (or 1/192) were used at times. this made the camera essentially two stops "hungrier" for light, but in any explosion- the clods of dirt that were normally smudgy within an individual frame ended up being sharp, adding a sense of hyper realism. going the other way (longer shutter speeds) results in more "smeariness" than normal, but also gains you additional exposure.
So, "Normal" shutter angle at 24fps is 1/48 or 180 degrees. A short shutter angle of 1/96 or 90 degrees makes the camera want one more stop of light, but can begin to "freeze" action that otherwise may be blurry. A long shutter angle of 1/24 or 360 degrees gives you an extra stop of light, but movement in the frame will look more smeary than "normal"

Complications arise with lighting that flickers (even though our eyes can not see it) at a rate that conflicts with the shutter angle you have chosen. Good news is that with the Red, you will see it happening in the monitor. there are various way (charts in American cinamatographer manual for example) that help you figure out what is safe given your frame rate and Hz rate of lighting. Fluorescents and HMIs are examples of possible flicker sources. hope that was simple enough.

[cinemano]

Thanks Natec.. very good explanation.. This is embarrassing, I actually thought the RED had the ability to physically 'bend' the shutter into any degree angle .. so its really shutter speeds they're talking about for those used to video bakground.. ? so Angle and Shutter speed is like comparing centimeter and Inches. They are the same thing, just diferent way of seeing it :) ?

Then it gets also confusing cos in the RED menu, you can do both the Shutter speeds and shutter angles.. so i always thought they were seperate features..

[David Birdy]

Great stuff!

The shutter in the Red camera, and many other video cameras are electronic in nature and limit the amount of light hitting the senor to "Mimic" the way a mechanical shutter operates.

I'm thinking the frame rate has more to do with the "flicker" from AC sources than the shutter speed. Anybody want to agree or disagree?

I love Reduser for the opportunity to engage in "techie talk"

Pocket protectors out & ready!!!:ohmy:

Dave

[David Mullen ASC]

Visible HMI "flicker" is due to variations in exposure frame-by-frame due to the interaction of the frame rate / shutter speed of the camera and the hertz pulsing of the AC discharge lamp.

Frame rate matters mainly in that, when combined with shutter angle, it affects the shutter speed, but the key really is shutter speed, assuming that the frame rate is constant (with a film camera, that's not always true if using a "wild" motor that is not crystal-sync.)

If you want to see what shutter angles and frame rates are "safe" for 60 Hz and 50 Hz lighting, look here:

http://www.panavision.com.au/Information/Flickerfree60Hz.htm
http://www.panavision.com.au/Information/Flickerfree50Hz.htm

In terms of shutter speed at 24P/25P affecting the classic "film look", there is little difference between 1/48, 1/50, and even 1/60, it's just a minor difference in the amount of motion blur pre frame.

[Curtis Abbott]

I have been on a few shoots where we had problems with flicker using tungsten lights shooting at 48 fps with the default shutter (180 degrees, I think) The panavision link david linked says to have it at a 144 degree shutter.

David do you think this would solve the problem? I will test the next chance I get.

Thanks for the link david.

Curtis

[David Mullen ASC]

I have been on a few shoots where we had problems with flicker using tungsten lights shooting at 48 fps with the default shutter (180 degrees, I think) The panavision link david linked says to have it at a 144 degree shutter.

David do you think this would solve the problem? I will test the next chance I get.

Thanks for the link david.

Curtis

Yes, 48 fps with a 180 degree shutter is not flicker-free for 60 Hz AC discharge lamps using older magnetic ballasts, like your typical overhead fluorescent, streetlamp, etc. I just had that problem the other day - the director wanted to go slow-motion in a room with overhead fluorescents, and the max speed of our camera was 50 fps so I had a limited number of choices in terms of frame rate and shutter angles. We ended up, I think, at 40 fps with a 180 degree shutter, but I could have gone to 48 fps with a 144 degree shutter or 50 fps with a 150 degree shutter. But the difference was that 40 fps with a 180 degree shutter was a 2/3-stop loss but the other two options were a 1 1/3-stop loss, or something like that.

[Douglas Underdahl]

Page 42, THE 16MM CAMERA BOOK, says the formula is

safe fps = 4xLxA divided by 360xI

Where

fps is frames per second
L is line frequency, e.g. 50 or 60
A is shutter angle
I is any integer greater than zero

So let's say you've got a camera with 172.8 degree shutter angle in Europe and you want to generate a list of safe speeds, so

4 times 50Hz times 172.8 is 34,560, divided by 360 times 1 = 96 fps safe speed.

Another safe speed would be 34,560 divided by 360 times 4 = 24 fps.

Where this could fail is that the line frequency is not precisely controlled. Some countries have imprecise line frequency or you might be using a generator that has a varying frequency. I remember Cinetronics or Cinematography Electronics sold a frequency meter that you could use to test lights and monitors.

Of course now, this situation is not nearly so bad with a RED (as opposed to a film camera) because you can certainly shoot a take and watch the monitor for flicker. You can even turn the joystick knob when in the fps or shutter angle select menu and watch for flicker.

[Curtis Abbott]

Great! Thanks for the information. This will help for the next time I run into this situation.