Tune out flicker from CRT

[nigelsmith]

Hi
WE have been trying to get rid of flicker from a CRT that will be in shot.
Usually I'd recommend using an LCD or Plasma to get round the issue, but the art department need it to be an old CRT.
I've done this before with Eclair ACL and Arri SR2 using varispeed, and was expecting to manage it in synchro mode.
However it seems to only work when I adjust shutter speed phase setting.
Just curious to know, why won't synchro mode do the job.
NB this is a PAL CRT we are using.
Thanks for any info.

 

[John Marchant]

In my experience the Red One doesn't have the very fine control of shutter speed needed to perfectly match with CRT's. You obviously need to work in multiples of 50hz, but if you're familiar with ENG cameras, the setting you're missing is the 'clearscan' or similar, which allows very fine adjustment of shutter speed in the 0.1's of HZ around the 50-60hz area. Simplest option is to work with a less filmic 360 degree shutter, but even here you might see a rolling line as the camera's read/reset happens.

If this is a controlled studio environment there's a chance that you may be able to hash together a sync from the R1's SDI out that you can lock whatever is supplying the image to the CRT to, but its a long shot dependent on what factors you have control over. Cheap old 14" PVM's are good for looking like old TV's, but actually having pro-grade inputs that might help you out.

 

[nigelsmith]

Cheers John.
I was expecting synchro mode to operate like CLS.
Sync lock is unfortunately not possible with the TV in question.

 

[Dan Hudgins]

Shouldn't PAL VITC be non-drop-frame 25fps?

If so than can't you convert VITC into LTC and feed that into the camera to phase lock to?

That would depend on the VITC being in sync with the video frames, but shouldn't that be what the VITC mixer box puts out in its PAL output? Or is the VITC going to be random in relation to the image frames? The VITC box should lock the non-drop-frame frame digit flip to the even/odd field retrace.

If you can get the VITC in sync, the convertor box should output in sync LTC as well since it just reads the bits and sends them out as audio signal.

If the cameras SMPTE LTC in is working right it should hold to better than 1ms error on the frame digit count plus or minus the phase constant. Then you just try to phase the roll-bar to be during the sensor "dwell" time if you are shooting 172.8 degrees or 180 if you are shooting 25fps.

 

[ericyoung]

Hi
WE have been trying to get rid of flicker from a CRT that will be in shot.
Usually I'd recommend using an LCD or Plasma to get round the issue, but the art department need it to be an old CRT.
I've done this before with Eclair ACL and Arri SR2 using varispeed, and was expecting to manage it in synchro mode.
However it seems to only work when I adjust shutter speed phase setting.
Just curious to know, why won't synchro mode do the job.
NB this is a PAL CRT we are using.
Thanks for any info.

Just to clarify, you have selected:
Sensor>Shutter>Mode>Synchro (not Normal or Relative)
and only then adjusted the Synchro value between 10 and 90, and then the Phase value between -45deg and +45deg.?

This may seem obvious, but I'm not the only one to have been scratching their head the first time I tried to use Synchro on the Red One. Initially, I just tried adjusting the Synchro and Phase values (and the values do change in their windows), and fooled myself into thinking the flickering/banding was changing, whereas in fact they were having zero effect until I also selected Mode to Synchro.