Jump to content


Photo

Question about refresh rate on computer when shooting 16mm


  • Please log in to reply
18 replies to this topic

#1 eekamouse

eekamouse

    New

  • Basic Members
  • Pip
  • 1 posts
  • P.A.

Posted 27 November 2005 - 01:39 AM

My bad if this has been asked before. So I'm shooting an indoor scene on an Arri S 16 mm camera. Fuji ETERNA 250-D film and an 80A filter. I'm wondering what I could do to eliminate the lines in the finished product, if there will be any..Sorry, I'm an Arri S newb.
  • 0

#2 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19759 posts
  • Cinematographer
  • Los Angeles

Posted 27 November 2005 - 11:07 AM

Make life simple for yourself and use an LCD screen for the computer. You probably don't have the resources to sync a computer CRT screen to your camera.
  • 0

#3 Andy Sparaco SOC

Andy Sparaco SOC
  • Sustaining Members
  • 203 posts
  • Cinematographer
  • Chicago and most airline lounges

Posted 27 November 2005 - 11:32 AM

Shoot at 29.970. A Crystal controlled variable speed motor can do that. You can rent them for a day.
You should be able to see the scan linesflicker if you need to adjust the camera speed even more then that.

You can loose the filter. An 80A is for converting Daylight to Tunsten used with Tungsten balanced film. Check the monitor set up there may be a 5600K (daylight) setting. Most monitors trend toward daylight not Tungsten (3200K).

In any case you can handle any slight color mismatch in the Xfer

Edited by asparaco, 27 November 2005 - 11:38 AM.

  • 0

#4 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19759 posts
  • Cinematographer
  • Los Angeles

Posted 27 November 2005 - 01:04 PM

Shoot at 29.970. A Crystal controlled variable speed motor can do that. You can rent them for a day.
You should be able to see the scan linesflicker if you need to adjust the camera speed even more then that.


He's shooting a computer screen, not a TV screen. They don't all run at 29.97 fps.
  • 0

#5 Robert Edge

Robert Edge
  • Sustaining Members
  • 401 posts
  • Other

Posted 27 November 2005 - 02:36 PM

Make life simple for yourself and use an LCD screen


Besides, unless it's your intent, if you use a CRT screen your film is rapidly going to look like a period piece :)
  • 0

#6 Andy Sparaco SOC

Andy Sparaco SOC
  • Sustaining Members
  • 203 posts
  • Cinematographer
  • Chicago and most airline lounges

Posted 27 November 2005 - 03:46 PM

He's shooting a computer screen, not a TV screen. They don't all run at 29.97 fps.


29.970 is a good place to start,especially with a LCD Monitor which are progressive and may not flicker perceptably. With the camera unloaded you can dial up or down a crystal controlled variable speed motor until the phase bar disappears. Then load and shoot. The tach and a non Cryatal controlled variable speed motor will not be critical enough to shoot a screen.

The proper motor is the key factor.

Edited by asparaco, 27 November 2005 - 04:18 PM.

  • 0

#7 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19759 posts
  • Cinematographer
  • Los Angeles

Posted 27 November 2005 - 08:34 PM

29.970 is a good place to start,especially with a LCD Monitor


It's not necessary with an LCD monitor, which is the entire point of using one! I've shot plenty of 24 fps material of an LCD screen. Plasma screens, on the other hand, might still pulse visibly.
  • 0

#8 Andy Sparaco SOC

Andy Sparaco SOC
  • Sustaining Members
  • 203 posts
  • Cinematographer
  • Chicago and most airline lounges

Posted 27 November 2005 - 09:25 PM

It's not necessary with an LCD monitor, which is the entire point of using one! I've shot plenty of 24 fps material of an LCD screen. Plasma screens, on the other hand, might still pulse visibly.



Yes LCD's are pretty stable-and I have shot lots of film and video of them and CRT monitors and the only thing consistent is that they were all different and they can all flicker noticably on film or video.

Being prepared and well informed to options and solutions seems only sensible-so many of the technical discussions are for the benefit of folks trying to solve a problem.

There are other good reasons to shoot 30fps for monitors but they don't address the orginal question.
  • 0

#9 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19759 posts
  • Cinematographer
  • Los Angeles

Posted 28 November 2005 - 01:38 AM

I've never had an LCD screen flicker when shooting at 24 fps. Besides, why would 29.97 fps be any better??? Like I said, we're talking about COMPUTER monitors, not NTSC TV sets. Computer monitors don't necessary run at 29.97 fps -- they have all sorts of refresh rates.

He's got an Arri-S -- so his best bet is to shoot an LCD screen. Keep things simple.

Generally for computer CRT screens, the solution is either to run the camera at the refresh rate of the computer, or reset the refresh rate to a speed that you want the camera to run at, then phase the camera to the computer. On my last film, we had to have someone come in with a computer CRT monitor set to run at 24 fps so we could sync to it and shoot dialogue.

On the film before, we had a prop CRT monitor that housed a LCD screen, so we didn't have to do anything to sync to it -- and I'm talking quite a bit of 24 fps footage shot by me and then later, second unit. No problems, no flicker.

Edited by David Mullen, 28 November 2005 - 01:45 AM.

  • 0

#10 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 11938 posts
  • Other

Posted 28 November 2005 - 11:04 AM

Hi,

> a LCD Monitor which are progressive

All non-obsolete computer displays are progressive, regardless of how you display them.

Phil
  • 0

#11 Andy Sparaco SOC

Andy Sparaco SOC
  • Sustaining Members
  • 203 posts
  • Cinematographer
  • Chicago and most airline lounges

Posted 29 November 2005 - 07:48 AM

I've never had an LCD screen flicker when shooting at 24 fps. Besides, why would 29.97 fps be any better??? Like I said, we're talking about COMPUTER monitors, not NTSC TV sets. Computer monitors don't necessary run at 29.97 fps -- they have all sorts of refresh rates.


Yes LCD's don't flicker but the flouresent tubes which backlight them can and do. Stand infront of a burn in rack with a a couple hundred LCD monitors on a manufacturers production floor (as I have done in HK and China) and it is obvious. Where do the "flickering" LCD monitors go -to the US as B stock and no name brands.


For the purposes of this thread you're advice is absolutely correct

until it is not correct and the user has a flicker or roll bar in the monitor being shot.
  • 0

#12 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 11938 posts
  • Other

Posted 29 November 2005 - 07:55 AM

Hi,

Some may flicker - I've seen it as a pulsation in video - but I can't see how you'd ever end up with a rollbar on an LCD. Any LCD which flickered visibly to the naked eye would be a reject at any end of the market.

Phil
  • 0

#13 K Borowski

K Borowski
  • Basic Members
  • PipPipPipPip
  • 3905 posts
  • Camera Operator
  • I.A.T.S.E. Local # 600 Eastern Region

Posted 29 November 2005 - 08:31 AM

I agree. You want to go with an LCD for shooting; it makes things so much easier. As an aside, early computer monitors, I believe for the Commodore platform actually had monitors with adjustible scan rates, so you could synch them with little more than a video tap and a lot of patience. Going back to what R. Edge said he is very right that CRTs are going to date your film. With the constant hype of the computer world, it is very unlikely that you will see CRTs except for in specialized graphics applications or very underfunded schools in the next five years. I was watching reruns of an old cancelled TV show, Space: Above and Beyond, set about 80 years in the future, and the first thing that struck me as "funny" right off the bat were the CRTs that they had in their futuristic hospital room. I'd say that those CRTs have dated the show more than its CGI has. In any case, best of luck with your film project.

Regards.
~Karl Borowski
  • 0

#14 John Pytlak RIP

John Pytlak RIP

    (deceased)

  • Sustaining Members
  • 3499 posts
  • Industry Rep
  • Rochester, NY 14650-1922

Posted 29 November 2005 - 09:37 AM

Any light source that responds rapidly to fluctuations in current will flicker at the frequency of the current. So fluorescent lights, HMI, mercury vapor and sodium vapor lights all flicker at the line rate when powered by AC current. "Flicker free" lights either are powered by DC current, or an AC current at a higher frequency that does not interact with the camera frame rate. Tungsten lamps have minimal flicker because of the "thermal inertia" of the glowing tungsten filament.

One quick way to determine if a light source is flickering is to use a loaded silicon photocell connected to an audio amplifier. This will allow you to "hear" the flicker frequency of the light. For example, a fluorescent light powered by 60Hz AC will have a 120Hz buzz. A light with no flicker will produce no sound.

Here is a simple description of how to"hear" light:

http://www.sofia.usr...my/section3.pdf
  • 0

#15 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 11938 posts
  • Other

Posted 29 November 2005 - 10:09 AM

Hi,

LCD backlights are invariably run by a Royer oscillator, which produces AC output at a frequency determined by the resonance of its inductor. This is usually many kilohertz, and I have never seen an LCD display that doesn't work like this, including line-powered equipment such as LCD TVs. If the backlight flickers visibly, it is faulty, and I very much doubt it'd do more than pulsate slightly on film.

Phil
  • 0

#16 Andy Sparaco SOC

Andy Sparaco SOC
  • Sustaining Members
  • 203 posts
  • Cinematographer
  • Chicago and most airline lounges

Posted 29 November 2005 - 10:18 AM

Hi,

Some may flicker - I've seen it as a pulsation in video - but I can't see how you'd ever end up with a rollbar on an LCD. Any LCD which flickered visibly to the naked eye would be a reject at any end of the market.

Phil


Flicker for LCD Roll bar for CRT both I consider a defect. We seem to be talking at different things at different points and we are past the point of being helpful to the orginal question. As we all know everything goes perfectly in production and we need not know how to address a problem that does not exist. And when I set up a shot in a room full of LCD monitors (as I have experienced in the past) and the Agency CD asks why some of those monitors are pulsing -I will show him this thread and assure them that they are not
Time to leave this thread forever <_<

Edited by asparaco, 29 November 2005 - 10:51 AM.

  • 0

#17 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19759 posts
  • Cinematographer
  • Los Angeles

Posted 29 November 2005 - 12:15 PM

You still haven't explained why shooting computer monitors at 29.97 fps solves this problem, since they don't all run at that speed...
  • 0

#18 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 19759 posts
  • Cinematographer
  • Los Angeles

Posted 29 November 2005 - 01:57 PM

Here are some remarks from the ASC Manual article on the subject, written by Bill Hogan and Steve Irwin:

North America and many other countries of the world have a television standard that displays 30 frames per second. Computer monitors can have refresh rates ranging from 50 to over 100 frames per second. The difference in frame rates is the predominant difficulty in photographing televisions and computers as part of a scene.

COMPUTER MONITORS

...When photographing a single computer monitor "insert style" and where you can shoot at non-standard frame rates, a manual speed control and some way to measure the computer monitor's refresh rate are required. There are two well-known film industry optical frequency meters that allow you to measure a monitor's exact frame rate and then set that rate into the speed control.

Computer monitors are generally non-interlaced, but this has little impact on shooting them. Since some computer monitors can display very high refresh rates, it is possible to photograph them at high speeds. For example, a computer monitor with a 96 Hz refresh rate can be photographed at 48 frames per second. The exposure time of 1/96 of a second matches the amount of time it takes the monitor to display one complete image.

LCD MONITORS AND PROJECTORS

This is often referred to as the "easy one". A majority of LCD computer monitors and projectors can be photographed without regard to matching frame rates. The light sources and image forming technology known as "active matrix" creates a picture that is continuous and always on, as far as the film camera is concerned. Laptop computers fall into this category as well. There are some low-end LCD technologies, still in use today, known as "passive" or "dual scan". These are not part of the "active matrix" type and may photograph with some breathing or flicker in the image....
It is possible to over or undercrank to some degree on most LCD display technologies. Unfortunately, the only way to find the limits are to run a battery of tests on the exact model you are going to use.

END QUOTE

I don't mean to drag this on, I'm only concerned because when some beginner asks how to shoot a computer CRT monitor with an Arri-S, the advice to get a crystal-speed 29.97 fps motor is not really correct, although he may have gotten lucky and it may have been the speed his monitor was running at, but it would be an expensive mistake should it have not worked. It would have been the correct advice should he have been shooting an NTSC CRT monitor.

For a beginner, the LCD screen solution is the simplest and works 99% of the time, and if he was really concerned, he could shoot a test.
  • 0

#19 Andy Sparaco SOC

Andy Sparaco SOC
  • Sustaining Members
  • 203 posts
  • Cinematographer
  • Chicago and most airline lounges

Posted 01 December 2005 - 09:44 AM

We are beating this thread to death, the world is a big place absolutes can bite you in the ass. Seems to be room for more then one opinion on this matter: (see the link for complete posting)

nuff said

http://www.tobincine...com/page54.html


"Quote"

6. Filming From Computer Monitors. This is a real no-man's land as each computer sub-model seems to drive its monitor at a different speed. Ideally use a photoelectric frequency meter to determine the ideal filming speed, or else run the camera without film while playing with the pushwheel switches to establish it. For the better quality non-interlaced monitors try the range of 25 to 46 FPS. For interlaced monitors try 12.5 to 23 FPS. The modern trend in newer IBM-compatible computers is towards a 75 Hz vertical refresh rate, implying a filming rate of 37.5 or 18.75 FPS. Use of the phase button is identical to that in section 5 above.

http://www.cinematog..... monitors.htm

"Quote"
Yikes,

I plan to shoot a computer monitor, it doesn't have to be in sync - just a quick shot of someone looking at a gay porn internet site while at work (yes, it is a comedy). I suppose the solution is as simple as renting a cinematography electronics synchronizer, placing it behind the monitor, and away we go ?

I realize that computers run at diferent speeds than monitors - Macs run at 75hz ... does this mean the speed will be about 37.5 fps?

The camera is an Aaton XTR.

Thanks so much in advance for any help,

Duraid Munajim


--------------------------------------------------------------------------------

>I plan to shoot a computer monitor...I suppose the solution is as simple as renting a >cinematography electronics synchronizer, placing it behind the monitor, and away >we go ?

That is basically correct, you then need to move the phase bar off the screen by looking at the monitor full frame in the camera viewfinder, while rolling the camera with the magazine removed. You turn the phase control on the sync box until the bar is moved off the bottom or top of the video screen while the camera is running. Then you can load the camera and shoot, knowing that the camera will run in sync and the phase bar will be not visible on the film.

There is one pitfall that you must be careful of: if you place the sync control's inductive pickup near the power transformer of the monitor, you might sync to the line frequency, not the monitor refresh rate. Bummer! Beware if the frame rate suggested by the sync box is exactly half of the local line frequency. (my note: 60HZ = 30fps)Move the pickup around until you get the monitor refresh rate. This only gets weird if the refresh rate is close to the line frequency, then you have to analyze what you see in the phase test to be certain that the phase bar is stationary relative to the edge of the monitor, before you move it off the screen with the phase knob on the sync box.

Bill Bennett Los Angeles


--------------------------------------------------------------------------------
>when I've shot computer commercials I've generally re-set all the monitors in shot to >run at around 60, I say around 60 because they're not that accurate, and locked the >camera to that.

I suppose that as long as they can stay put at 60 for the length of the shot, it would suffice. When filming a lot of montitors, this would seem to be the way to go.

Time to take another look at the PC. If I can make it run at 60, all I would have to do is run the camera at 29.97.

Hmmm...

Maybe I'll rent the synchronizer just in case

BTW, thanks for all the answers - I feel less foggy about the situation.

Duraid Munajim Montreal(-24 Celsius), Canada


In any case a crystal controlled variable speed motor would seem a good solution regardless of what you may be forced to work with-my opine only

Edited by asparaco, 01 December 2005 - 12:50 PM.

  • 0


Opal

Paralinx LLC

The Slider

Broadcast Solutions Inc

CineTape

Glidecam

Ritter Battery

CineLab

Media Blackout - Custom Cables and AKS

Metropolis Post

rebotnix Technologies

Gamma Ray Digital Inc

Aerial Filmworks

Tai Audio

Wooden Camera

Willys Widgets

FJS International, LLC

Visual Products

Abel Cine

Technodolly

Rig Wheels Passport

Technodolly

Opal

Media Blackout - Custom Cables and AKS

Metropolis Post

Willys Widgets

CineTape

rebotnix Technologies

CineLab

Broadcast Solutions Inc

Glidecam

Aerial Filmworks

FJS International, LLC

Abel Cine

The Slider

Ritter Battery

Paralinx LLC

Tai Audio

Wooden Camera

Visual Products

Rig Wheels Passport

Gamma Ray Digital Inc