How does synchro scan shoot TVs & monitors?

dogman-x

dogman-x

Active member
Sorry, but I've looked around the forums and really scratched my head here, and I'm still a bit confused.

If I'm shooting 24p and the computer screen is 60 or 75 Hz, how does the shutter speed angle help make the computer monitor look solid?

Also, for TVs at 30 or 60 fps.

I still don't understand the concept. If the HVX is on 24p, and the TV or monitor is not, how does syncho scan help?
 
It's only really an issue for CRTs, and it becomes an issue because CRTs work by getting zapped by an electron beam which causes the phosphors to glow, and then they immediately begin to decay (or fade darker). So the difference in brightness from the beginning of the frame to the end of the frame can be huge.

If you match your exposure time (not your frame rate, but your exposure time) to the sweep rate of the CRT, you'll guarantee that you're catching every line at a consistent exposure. If you don't match the rate, then not only will some lines be darker than others (which exhibits itself as a dark band on the screen) but the band will in fact move up or down depending on how far out of sync you are.

On LCDs or other types of displays there's not really a sweeping electron beam drawing the image, it's basically that every pixel gets set to a fixed brightness and "stays there" so there's not the same issues.

On a TV you want to be shooting at a fixed rate of 1/60th (or, in PAL territories, 1/50th). On a CRT computer monitor you want to set your shutter speed to match the refresh rate of the monitor.
 
Barry,

Thanks. My head doesn't hurt so much any more. Just to be sure, let me play it back to you:

1) If you're shooting a flat screen TV or computer monitor, then don't worry about it - just set the shutter to 200d or whatever looks best for the rest of the shot. Flat screen monitors will look good.

2) If you're shooting a CRT TV or computer monitor, then you need both the frame rate and the shutter speed just right, or it won't look good. If the frame rate is off, then you'll get moving bands. If the shutter speed is off, the CRT image will look uneven (stationary band).

So if you're shooting in 24p:
a) don't shoot CRT TVs (unless you can somehow change it's field rate)
b) shoot CRT computer monitors adjusted to 72 Hz refresh rate with HVX shutter at 120d.

Have I got this right now?
 
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It's a lot easier than that. Just look in your camera's LCD -- if you see a dark band or a scrolling band, then you know you need to adjust your syncro scan to minimize or eliminate that band.

LCDs and plasmas shouldn't offer the same kind of trouble that CRTs do. You should be pretty much good to go when shooting one of those.

When shooting a CRT TV, just set the shutter speed to 1/60th and it should become crystal clear.

When shooting a CRT computer monitor, you want to match your syncro scan to the refresh rate of the monitor, and then adjust until any dark or scrolling band goes away. You may end up with a thin stationary dark line but there's not a whole lot you can do about that.
 
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