Sync TV Images

[Sam Care]

Hi,

 

I have a couple of questions.

 

Firstly when shooting a TV playing video footage, how do I syncronise it with the camera. I am shooting a TV used in the UK, with a S16 Arri SR2. I heard that Arri hire out a sync box (might be called PSU?), does anyone know about this? Is it just the frame rate that I have to sync up or is it the shutter angle too, because I don't think the SR2 has a manually adjustable shutter angle?

 

Secondly, I was reading an article in which Harris Savides said that the contrast of the film changes when shooting at a higher f-stop. So does that mean that if you shoot at a lower f-stop you get more contrast or is it less and how much of a change actaully occurs? I guess that this, and the change in depth of field, is why some DPs like to shoot a whole scene at a consistant f-stop.

 

Cheers

Sam

[John Ealer]

What frame rate are you shooting at? If you're shooting a PAL TV at crystal 25fps with a 180 degree shutter, you'll need the sync box if you want to position the very small "roll bar" off-screen. If the TV is just in the background, you probably can get away with the sync box, since this "roll bar" won't be that noticeable. If the TV is in the FG, you'll definitely want to be able to position this line in the vertical blanking interval of the TV.

 

If you're not shooting 25fps, then you also need to adjust the shutter angle of the camera so the shutter speed of the camera matches the scan rate of the TV. If you're shooting a PAL TV at 24 fps, for example, you'd need to have the shutter set to 172.8 degrees, which will minimize the roll bar to virtually nothing. Then you'd need the sync box to position it off screen.

 

F-Stop, in and of itself, will only directly affect contrast to the very, very limited extent that the contrast characteristics of a lens change with aperture setting. As you said, one of the principal reasons to keep F-stop the same throughout a scene is to try and keep depth of field consistent between shots, especially when you're shooting narrative-style coverage. Under or overexposure (which is only indirectly related to F-stop) will affect contrast. Significantly under or overexposed images will tend to be less contrasty since you're putting more image information on the toe and shoulder of the gamma curve, which has an inherently lower gamma.

 

J

[Alvin Pingol]

In addition to lens characteristics affecting contrast with different apertures, shooting at wider stops can give the appearance of lower contrast, for the background becomes more out of focus as depth of field is reduced. Light areas and dark areas in the BG will blur into each other, effectively reducing contrasts - Accordingly, stopping down will bring things into focus, thereby making contrast differences more apparent.

[Robert Hughes]

Are you needing to shoot an actual TV running the video program, or can you matte out the screen? If the latter, then you may want to use a kinescope to transfer the video to film.