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Filming projections

G

gregmetcalfe

hello all,

I was wondering if anyone could suggest how to get rid of flickering or strange waves of light or bars of colour the appear whenever I try filming projections.
We're filming on a Canon 5D so its in progressive, and so far we've had the same problems whichever input we use on the digital projector. We've tried playing around with the shutter speed and with the refresh rate on the computer we're playing the videos to be projected from but with limited success.
Can anyone help?!

Thanks,
Greg
 
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It could also be moire.

Check out this video and focus on the roof. Does your issue look anything like this? This is moire:

https://www.youtube.com/watch?v=m6eKV9nu2Ao&feature=player_embedded
 
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doesnt look like that, no. suppose thats at least one problem we've dodged. it looks fine for when we're shooting normally, its only when there's a projection in the shot.

thanks for the tips guys, i'll keep experimenting.
 
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Could you upload a video clip with the problem? The way you've described it sounds a bit like a shutter speed mismatch, but it's hard to tell. The only other thing I can think of is perhaps the rolling shutter on the camera is causing problems. What shutter speed/refresh rate combinations have you tried?
 
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Jamster said:
Guys it will be great if you can explain about such ´frame rates´etc. maybe via a chart or such, so we can avoid the same problem down the road.

Cheers, Jim.
Click to expand...

"Frame rate" means frames per second, and shutter speed is how long the shutter is open for. Shutter speed is expressed as a fraction of a second when working with DSLRs and other stills cameras (e.g. 1/50) or in degrees when working with high-end video and film cameras (e.g. 180°).
 
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Jamster said:
Sorry guys I wasn´t clear - what I meant is there a ´rule of thumb´in terms of avoiding said flicker - as in a graph, chart or basic equation?
Click to expand...

Every frame needs to be exposed to the same number of AC pulses, which varies depending whether you live in a 50Hz or 60Hz country (e.g. the UK and USA respectively). If you're in the UK and shooting 25 fps with a 1/50 (or 180°) shutter, you're getting two pulses of light per frame - go to 50 fps and 1/100 (or 180°) and you're getting one pulse per frame. There are some lookup tables from Panavision for 50Hz and 60Hz countries, but the shutter speed section isn't that useful if you're dealing with fractions rather than degrees.
 
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