Rolling Shutter Fluorescent?

[abook]

Maybe do a test where you pan up and down, showing that the scan either follows or does not follow the frame. Also try one locked off.

The shot is handheld so it is moving up and down, I've got a few examples I'll post later including a still of the r3d, and hopefully a different shot where the banding showed in a different location as well.

abook

 

[abook]

Our shutter works in a similar way in that the 'blades' of the shutter are equivalent to the start of the exposure and end of the exposure. The main difference is rate at which the blades move across the frame.

Deanan

http://www.mediabutton.com/proofs/misc/red_band2.mov
beware the quality

There is an answer I was hoping for. Question though, film spinning shutter flickers because of the way it 'wipes' a frame, but looking at the video it looks like the CMOS is almost synced with the flourecents frequency because the banding seems to very slowly move upward, the same as the computer screen example. The thing that gets me, is that it doesn't flicker, it bands.

The video frame looks separated into approximately 4 different scanned areas, which to me means that the lower end of the fluorecents frequency is exposed on scan 2 and 4, while the upper end is on 1 and 3, thus the banding not the flickering... I guess that wasn't a question.

abook

 

[Deanan]

What shutter were you shooting at?

 

[abook]

http://www.mediabutton.com/proofs/misc/bandingfrm.jpg

Here is the r3d still. The post workflow ain't the issue.

 

[abook]

Shutter: 1/48, ASA: 320, wide open, 3880 kelvin

 

[Deanan]

If you can try it again, switch to 1/30th or 1/60th(assuming your ac runs at that). If the flouros are off by quite a bit then try to adjust the synchro and phase.

 

[abook]

If you can try it again, switch to 1/30th or 1/60th(assuming your ac runs at that). If the flouros are off by quite a bit then try to adjust the synchro and phase.

I'll give her a shot on both, thatnks for the help.

abook

 

[Dj Joofa]

looking at the video it looks like the CMOS is almost synced with the flourecents frequency because the banding seems to very slowly move upward, the same as the computer screen example. The thing that gets me, is that it doesn't flicker, it bands.

I posted the following reply sometime ago:

The amplitude of these bands depend upon exposure time, frequency should remain constant, and the scrolling between frames (i.e., phase difference) is due to frame rate (beat frequency between frame rate and flicker frequency). Hence, if frame rate is matched correctly, then the scrolling should stop, but the static banding should stay there.

However, in theory, if exposure time is properly matched, then there is no need to match frame rate, as the amplitude of flicker has been made to vanish.

If exposure time is not matched, then the amplitude of the flicker is reduced by selecting a larger exposure time, though, at the expense of more motion blur.

 

[abook]

Tried a test at 1/30 and 1/60, both were without the banding or flicker, though 1/60 was obviously under exposed. We also tried a Kino, at 1/30, 1/48, 1/60 and no banding or flickering occured. Just FYI.

thanks again

 

[Tim Sutherland]

Our shutter works in a similar way in that the 'blades' of the shutter are equivalent to the start of the exposure and end of the exposure. The main difference is rate at which the blades move across the frame.

Deanan

Except a CMOS scans top to bottom, and a film shutter rotates (nearly scanning) side to side, so there is a slight difference. I don't know exactly how that affects it, though.

 

[Barry Green]

Tried a test at 1/30 and 1/60, both were without the banding or flicker, though 1/60 was obviously under exposed. We also tried a Kino, at 1/30, 1/48, 1/60 and no banding or flickering occured. Just FYI.

thanks again

Yes, what you're seeing here is a rolling shutter issue. It won't happen at 1/40th, 1/30th, or 1/60th. With any other shutter speed you'll see it even more prevalently.

And it won't happen with a Kino because a Kino uses a high-speed electronic ballast.

If you're shooting under fluorescents, unless you can guarantee that they're high-speed electronic ballasts, you should set your shutter to 1/40th or 1/60th, and avoid 1/48th. The same advice applies for magnetic HMI's too. There are no "HMI-safe" frame rates for a rolling-shutter camera, but there certainly do appear to be HMI-safe shutter speeds. The two of most interest to NTSC-area shooters would be 1/40th and 1/60th.

If you're using electronic HMIs or fluos, you have nothing to worry about.

If you're using magnetic HMIs or fluos, you may have something to worry about depending on your shutter speed. If you're using a "relative" shutter (such as 180 degrees) then you'll almost definitely have a problem. If shooting under magnetic HMIs or fluos, force your shutter to "absolute" mode and choose 1/40th or 1/60th. (in 50Hz territories, choose 1/50th).

This info is based on testing a Red One Build 14 under magnetic and electronic HMIs and magnetic and electronic fluos, and Build 16 Alpha under a magnetic HMI.

 

[Steve Freebairn]

As has been mentioned, switch your shutter to 1/30, 1/60, 1/120 or whatever setting you have to in order to match what frequency your lights are being driven at. On the feature I'm working on, we've shot a lot of things at 144 degrees (1/60) and 288 degrees. I've noticed on shots that fluorescents don't always showing you a flicker, but sometimes show a band that moves slowly from the bottom to the top of the image, it's really easy to spot if you ff or rewind through your footage in FCP or Pr. There have also been a few instances where the magnetic ballasts on an 18k has made the RED LCD flicker and the Panasonic HD-SDI monitors flicker, but there was nothing on the footage at all, that freaked us out enough that we started using the 1/60th and 1/30th settings.

See this thread http://www.reduser.net/forum/showthread.php?t=12654&page=3&highlight=BALLASTS

 

[Stephen Williams]

Except a CMOS scans top to bottom, and a film shutter rotates (nearly scanning) side to side, so there is a slight difference. I don't know exactly how that affects it, though.

Hi,

Many film cameras scan top to bottom, it was only the combination of S35 & PL mounted lenses! Camera manufactures had to place the shutter at the bottom of the camera so the mirror shutter did not hit the back of the lenses, when the mount was moved from Academy to Silent (S35) apeture.

All Mitchell Cameras, Arri 2's, 3's Bl's, Ultracams & many (all?) Panavision & many others cameras were designed too & left the facory scaning side to side.

Stephen