Rolling horizontal green banding - what is is and how to eliminate

[Geoffrey Cox]

I notice a few threads on here about banding in the c100 though nothing that was helpful to be honest.

I shot some footage that features some wide green bands that roll continually down the frame. It disappeared when I lowered the shutter speed but a high shutter is what I needed. Fluorescent lights were everywhere. Hz rating was correct at 50 (UK/PAL).

It would be good to know what is exactly causing this and if there is any way to remove the bands in post (I have looked online but nothing really looked much use). I mainly use Premiere. Vimeo link to clip below:

20160509154618 on Vimeo

[Dan Brockett]

Typical roll bars. 50Hz is only part of the equation, the rest is shutter speed/angle. You could have dialed this out using Clear Scan, see page 54 of your owners manual. I assume this was under fluorescent or other discharge lighting? Often the ballasts of the lights age at different rates and unfortunately for us, can all be flickering at different rates.

I recall back in the day shooting S16 film in a Kinkos (copy shop here in the U.S.). Did a wide shot of the entire store which was lit with dozens of over head fluorescent panels. In the wide shot, to our delight, we counted ten different flicker rates. Really nothing you can do with multiple lights with multiple flicker rates. But for your shot, which is more if a MCU of one object, assuming it was mainly lit with just one panel or light, flickering at one rate, you could have dialed it out with clear scan.

[Geoffrey Cox]

Thanks for the info. There were hundreds of fluorescents in fact so dunno (big factory floor). Had no idea about clear scan though so useful tip.

I'm guessing trying to get rid now might not be worth the bother. Have plenty of good material but these shots captured the detail due to high shutter speed.

[Dan Brockett]

Originally Posted by Geoffrey Cox

Thanks for the info. There were hundreds of fluorescents in fact so dunno (big factory floor). Had no idea about clear scan though so useful tip.

I'm guessing trying to get rid now might not be worth the bother. Have plenty of good material but these shots captured the detail due to high shutter speed.

You didn't mention high speed shutter, that's your issue. Clear scan "might" have prevented this but that might not have been "high speed shutter", Clear scan would just let you dial this roll bar effect out. Higher speed shutter exacerbates this effect, it was the same in the film days, shooting high frame rates too.

[Seth Bloombaum]

Originally Posted by Geoffrey Cox

...Have plenty of good material but these shots captured the detail due to high shutter speed.

If you must have high shutter speeds for some of these closeup details, you'll have to light the scene with a continuous source like tungsten to avoid banding.

If you're unable to control the existing lighting at all (consult the plant's maintenance engineers / electricians) it may be that a very intense continous source like an added HMI would allow you to reduce exposure, thus reducing the banding produced by ambient lighting. That would need testing...

The problem you're dealing with is the ballasts in use on the fluorescent fixtures. Old style were magnetic, and put 50/60 Hz out to the tubes. Modern ballasts are electronic, and put out 20+ KHz to the tubes. This too is something to discuss with plant engineers, it may be that some areas have more modern fixtures, which don't show this kind of banding.