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Vertical vibration in projected image


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#1 Phil Rhodes

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Posted 21 August 2017 - 11:00 AM

Hi folks

 

last night, I watched Atomic Blonde (Alexa, Hawk vintage anamorphics, very pretty) in screen 4 of the Empire Leicester Square in London. Throughout the presentation, including the ads and trailers - so this isn't a camera problem - there was a very small vibration in the image which appeared to be almost entirely in the vertical plane. It was so subtle, it was only visible on high contrast lockoffs, and particularly on things like titles in the ads and trailers. The rate of the vibration appeared to be once per frame, for two distinct image positions per frame, making it look almost like interlaced scan on a standard-definition 25fps image.

 

I'm speculating wildly, but I was left wondering if they'd left the rotating filter assembly required for RealD's circular-polarisation stereoscopy in place and running. It's one of those awful subdivided multiplexes where there's no projection booth, just a box in the ceiling containing the projector, so it's not very obvious what's going on. The thing is, those things run at 144Hz, for a total of six switches per frame, so it really ought not to be visible. It looked fast, compatible with the idea of it being a 48Hz twitch, but not that fast. I can't imagine any other reason why that would happen, other than some part of the projection equipment suffering vibration due to something as daft as a very worn out fan.

 

The projection otherwise wasn't bad, certainly good enough to see the enormous variability in sharpness in those lenses, but - twitchy.

 

P


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#2 Phil Connolly

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Posted 21 August 2017 - 01:14 PM

Real D isn't mechanical - it uses a LCD electronic polariser, no moving parts. Dobly 3D uses a spinning disk - The Empire used to use dobly in the past - so if they still do it could be that?

 

If its single axis maybe something to do with timing? Mechanical vibration would have to be very specific to be perfectly on the vertical axis. 


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#3 Phil Rhodes

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Posted 21 August 2017 - 02:04 PM

Oh. My bad, got the tech mixed up. Yes. That. 

 

It did seem well-synchronised with the frame update.

 

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#4 Phil Connolly

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Posted 22 August 2017 - 07:08 AM

I've been boycotting the Empire since they killed screen 1


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