Filming monitors and TVs

You don’t see this all that often anymore, but if you played around with any kind of video camera before every screen was LCD, you probably remember seeing a sort of rolling bar on TVs or computer monitors when you filmed them. This happens basically because of a mismatch between the speed that monitor refreshes, and the shutter speed of the camera.

Since this movie is set in the 90’s, I’m dealing with an old CRT monitor and cathode ray TV, both of which feature prominently. So I’m trying to figure out the best way to deal with it.  

The easy way out would just be to “fix it in post” and slap the video over the film footage using After Effects or something.  I’ve done worse things before, but I don’t love this idea. For one, it kind of defeats the purpose of shooting on film if I’m going to cover up the film image with a digital one.  For two, I see this effect all the time, and it almost always looks bad to me. I have done similar things before, but I’d like to save it as a last resort in case the image turns out to be completely illegible.

So I think I’m going to be OK with there being a little bit of a rolling bar, I just want to figure out how best to control it.

Since I’m shooting on 16mm, there’s no way to really accurately see what it’s going to look like ahead of time. Luckily, using my trusty Canon T2i, I can do my best to approximate how it will look.  The most important part would be setting the shutter speed.

From my research I’ve determined that my camera (the CP16-R) has either a 135 degree or 156 degree shutter.  (Not sure which!) That means shutter speed at 24fps is either 1/64 or 1/55. Well, the T2i can do 1/60, so I’m gonna go ahead and use that to at least get in the same ballpark.

Great, so now I have something to look at (I also set the ISO and frame rate appropriately), now what can I do about controlling the bar?  Well, computer monitors have a refresh rate that can be controlled by software.  Yay, so that at least gives me a tiny bit of control. (I’m not sure there’s as much of an option for the TV.)

The driver on the laptop I’m using for playback gives me options for 60Hz, 70Hz, 75Hz, and more.  I’m hesitant to try too high of a refresh rate, because supposedly it could “permanently damage” the monitor to set it higher than what the monitor supports.  I don’t know what this monitor supports, nor can I find any information about it. (It was hard enough to track down a CRT monitor in this day and age!) I’m hoping 70Hz isn’t going to destroy it, and planning not to go above that.

So, I did some experiments, and this is how they look:

48 Hz
60 Hz
50 Hz
70 Hz

I’m pretty sure the way to get it in sync is to have a refresh rate of twice the frame rate. Shooting digitally the frame rate is technically 23.976, but on film it will be exactly 24. Therefore I believe that there wouldn’t be a rolling bar at all with the 48Hz refresh rate. However, as you can see, there is a pretty big dark roll that happens slowly on the digital version. I think the risk is that the roll wouldn’t move, but it could very well be sitting somewhere in that cycle, and I don’t have a way to know where it would be.

50Hz looks really bad, 70Hz is a little too spazzy for my taste, so I decided to go with 60Hz. It’s a slower and smooth roll, but without lingering the way it does at 48Hz.

I’m kind of shooting in the dark here, so here’s hoping it turns out well!

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