60 cycle monitor noise

[clashradio]

Hello, I realize this is an analog question but it somewhat applys. I have a Canon 814 xl-s Super 8 camera and I plan on shooting a scene with a computer monitor in the near background. Any ideas on which frame rate to shoot to get rid of the 60 cylce noise? Rates that the camera can be set to are: single frame, 9, 18, 24, and 36. I can adjust the speed in post via my NLE program.

[SLK001]

By "noise" are you referring to the apparent "scrolling" of a bright bar over a video display when shot by a TV camera?

If so, then you might not be able to get rid of it no matter what speed you select (it is really there, it's just that the eye can't detect it). It might be best to use an LCD screen for the computer monitor instead of a CRT type display. The effects will be much less.

And I doubt that you really can adjust the speed via your NLE program (and have it anything that you'll want to keep).

As always, TEST your configuration to see if it is what you really want BEFORE you go into "production".

[clashradio]

yes, I'm sorry. The scrolling or rolling bars. I didn't know if shutter speed or frame rate make any differnce. I've seen certain movies or whatever that show a tv in the background with no "bars"

[Cornucopia]

Yes, you have to match the frame rate of the camera with the monitor (or vice-versa). And sync the opening of the camera's shutter with the beginning of the picture display.

Computer CRT monitors usually sync at 60, 72, 75, 85, 100Hz, etc.
TV CRT monitors sync at 59.94Hz (NTSC) or at 50Hz (PAL)
Both have a moment where the screen is completely blank/black.

LCD monitors for either Computer or TV don't have that moment, they just refresh the pixel, so the "black" bar won't be there, but if the sync rate is wrong, it'll still look wrong on the camera image.

8mm film cameras CAN'T be adjusted to anything that'll work with any of these.
16/35mm film cameras can sometimes e.g.: The original Todd-AO spec had the 35mm cameras shooting at 30fps, which could then easily sync with 59.94/60Hz monitors.

Occasionally, monitors can be set for a different sync rate, but you have to have special equipment all around (monitors, vtrs, etc) and/or an engineer who understands how to mod and fix equipment. This means $$$$!

When using pro videocams, there is often a setting called "clearscan" that allows for minor adjustment of the sync in combination with a very high-speed shutter setting, that'll allow these bars to be minimized without actually modding either the cam, the monitor or both.

If you had a pro videocam and a pro monitor, both of which could take genlock/separate-sync, you could genlock both from a master source and everything would just naturally be in sync! That's the way to do it...

Scott

[redwudz]

For a TV movie, they may hook the video cameras' sync output to the TV so that both were using the same sync pulses. Not really practical with a home system, but a TV studio can do a lot of things. You could try adjusting your monitor settings, like refresh, to a higher number, maybe 85Hz if your monitor and video card can handle that, but I doubt it improves much. LCD monitors work much better for videotaping the screen.

For an experiment, you could try this with a TV set: Plug your camera composite output into the composite video in of the TV, then see if you can videotape the screen image. This may also work if the camera outputs a RF signal you can tune with the TV. Since the camera should be setting the sync pulses, you may get a stable picture on your tape. Of course it will be like looking into multiple mirrors, with images of the TV screen receding in the distance.

EDIT: Sorry, I saw 8mm and was thinking video camera, not film. Never mind.

[Cornucopia]

If you can do 24fps on your 8mm camera, setting an LCD monitor to 72Hz refresh would probably be the best option available to you...

Scott

[solarfox]

In the movies (and on many TV shows, as well), they use special video monitors which are electronically synchronized with the camera shutters in order to get rid of that "scrolling bright bar" effect. This, unfortunately, is a setup you'll have a hard time duplicating at home, as the equipment is rather specialized and probably not cheap...

That being said -- as it happens, 72Hz is an even multiple of all of your potential shutter speeds. (9*8=72, 18*4=72, 24*3=72, and 36*2=72.) So, you might try setting your monitor's refresh rate to 72Hz, if your monitor and card support that rate, and see if that gets you anywhere...

[guns1inger]

Cheaper (if not simpler) would be to superimpose a new screen display over the shot in post

[ozymango]

I've done this and while the results aren't perfect, definitely go with the 24fps on the camera and 72hz on the monitor. The biggest problem with non-pro 8mm film equipment is that you can't change the shutter speed/angle, which is a bit different than the frames-per-second speed.

That is, the shutter on your film camera is probably opening for 1/25 to 1/30 of a second for each frame you shoot, so it's not just a matter of how many frames per second, but the time the film is exposed each frame because that's where the "flicker" comes from. And because even a slight change in shutter angle/timing can make you "lose sync" with the monitor refresh, your computer screen is most likely still gonna look a bit "off." But at least it won't have big black bands moving across the screen.

It'd be nice to do a test reel, with a couple of different film rates and monitor rates to see just what kind of weirdness you encounter, but what's a roll of super 8 film cost today, for 3 1/2 minutes of film? $20? And another ten bucks (at least!) for processing?

Maybe you could dub the monitor in later?

[clashradio]

Thanks everyone for your help! Yes, super 8mm film is about $20 per cart for 2-3 minutes depending on which speed it's shot (18 or 24fps) + processing + frame by frame transfer to mini-dv tape but it's worth it for that nostalgic feel.

[Cornucopia]

Another thing to worry about is that the 8mm cam's spec may "say" 24fps, but because of mechanical parts being what they are, it might be 23.27???, etc. Try and sync that up!

Note also that even if you successfully deal with the frame rate and the shutter sync for static shots, if you MOVE THE CAMERA while shooting, you may have to readjust (even clearscan goes bad when you're mobile). This includes pans, zooms, etc.
Watch out!

Scott