Venetian Blind effect

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Digiimpact

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Venetian Blind effect

PostFri Nov 20, 2020 10:05 am

Hi
Just wondering if venetian blind effect is still prevalent in current cameras including BMD Cameras

Tony
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Kim Janson

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Re: Venetian Blind effect

PostFri Nov 20, 2020 10:31 am

To me it is not clear at all what venetian blind effect is though I can google.

Even less clear it is how it ever has manifested on BMD cameras.
LeViteZer Smooths the movement, www.levitezer.com
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Robert Niessner

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Re: Venetian Blind effect

PostFri Nov 20, 2020 10:56 am

Maybe he is asking about rolling shutter artifacts?
Robert Niessner
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Digiimpact

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Re: Venetian Blind effect

PostFri Nov 20, 2020 11:30 am

i Have this problem of say shooting a tv in a lounge room (Wide shot) very low lit and i get a line size if TV acroos the room slightly saturated and level a touch down. ... i seen it years ago on CCDs when say shooting Venetian blinds but in a room you gat a slight reversal of signal. from the venetians... Didn't think that happens in Todays Cameras but could be wrong.
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Digiimpact

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Re: Venetian Blind effect

PostFri Nov 20, 2020 11:31 am

a bit more to add.... G2 ISO about 1600
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Robert Niessner

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Re: Venetian Blind effect

PostFri Nov 20, 2020 12:04 pm

Oh you are talking about rolling bars due to a sync mismatch between camera shutter and monitor refresh rate.
That has nothing to do with advanced technology or not. It is a time aliasing artifact.

You have to set the camera shutter to the same frequency like the monitor your are filming.

For example if you are in PAL land with 50 Hz then you have to set your shutter to 1/50.
For NTSC TVs or most computer screens they are running on 60 Hz, therefor you need a shutter of 1/60.

Sometimes this does not work because screens might be set to an awkward refresh rate. Then you have to tap the shutter settings for the on-screen menu. There double tap the shutter value on the left side inside the < >
This opens an overlay where you can type in any exact shutter fraction you want. Like 1/59.788 or any degrees if you have set the camera to display shutter in degrees.

It is a bit of try and error to get the closest fitting value then.
Last edited by Robert Niessner on Fri Nov 20, 2020 12:05 pm, edited 1 time in total.
Robert Niessner
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Kim Janson

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Re: Venetian Blind effect

PostFri Nov 20, 2020 12:05 pm

if you mean stripes and flashing on video because 50 or 60 Hz light or worse them mixed, Try different shutter angle. 216 degrees usually works pretty good for me at 30 FPS.
LeViteZer Smooths the movement, www.levitezer.com
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Digiimpact

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Re: Venetian Blind effect

PostFri Nov 20, 2020 12:32 pm

Will try changing changing shutter speeds and see how that goes....
Thanks both for your responses
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Digiimpact

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Re: Venetian Blind effect

PostFri Nov 20, 2020 12:33 pm

Will try changing changing shutter speeds and see how that goes....
Thanks both for your responses
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John Brawley

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Re: Venetian Blind effect

PostFri Nov 20, 2020 7:09 pm

There's also this version of it as a problem.

https://johnbrawley.wordpress.com/2011/ ... ind-trick/

This is a CMOS sensor overflow from high overexposure when you can have a kind of bleed of image in high contrast areas. I first noticed it when shooting Venetian blinds.

JB
John Brawley ACS
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Currently - Los Angeles
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Digiimpact

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Re: Venetian Blind effect

PostSat Nov 21, 2020 11:58 am

Thanks John
Yeah i just got a replacement camera which was G2 but the other 3 G1 i have doesn't have it, on exactly the same shot?
i know it exists as i have a seen it before in my many years lol. BMD sent me your article but have had it on properly exposed shots too not too bad had to crush blacks not to-see it. just interesting why it only happens on this camera.
(Perhaps its the old Camera Tech in me).
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John Brawley

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Re: Venetian Blind effect

PostSat Nov 21, 2020 4:42 pm

Digiimpact wrote:Thanks John
Yeah i just got a replacement camera which was G2 but the other 3 G1 i have doesn't have it, on exactly the same shot?
i know it exists as i have a seen it before in my many years lol. BMD sent me your article but have had it on properly exposed shots too not too bad had to crush blacks not to-see it. just interesting why it only happens on this camera.
(Perhaps its the old Camera Tech in me).



Every sensor seems to have a different threshold for how bad the circumstances are before this can be triggered. I think it just depends...

JB
John Brawley ACS
Cinematographer
Currently - Los Angeles

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