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flickering problem


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#1 Chris Gloag

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Posted 21 December 2008 - 10:09 PM

http://exposureroom....853c82ddb5346d/

Any suggestion how to avoid the flicker on 30p video in PAL land?
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#2 Saul Rodgar

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Posted 21 December 2008 - 11:21 PM

Electricity is a bitch , isn't it?

Three options:

A. Change your camera frame rate to 25 to match PAL land's 50hz power rating.

B. Change PAL land's electric AC interval to 60 hz/ sec to match your camera's 30 fps.

C: Wait for a newfangled camera that somehow does it for you internally and automatically. ;)

Edited by Saul Rodgar, 21 December 2008 - 11:25 PM.

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#3 David Mullen ASC

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Posted 21 December 2008 - 11:41 PM

A. Change your camera frame rate to 25 to match PAL land's 50hz power rating.


You could also change the shutter to match 50 Hz.
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#4 Saul Rodgar

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Posted 22 December 2008 - 01:22 AM

Thank you. I forgot the clear scan option on camcorders, though the 50DII is unlikely to have it, you are correct.
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#5 Chris Gloag

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Posted 22 December 2008 - 01:36 AM

You could also change the shutter to match 50 Hz.

What would it be your suggestion in the 1/30th - 1/125th range? Thanks.
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#6 Emanuel A Guedes

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Posted 22 December 2008 - 06:28 PM

Here is some interesting info related to:

LINK I

LINK II
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#7 David Mullen ASC

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Posted 22 December 2008 - 06:35 PM

What would it be your suggestion in the 1/30th - 1/125th range? Thanks.


Usually it would be 1/50th for 50 Hz lighting. But you can also dial it in using ClearScan.
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#8 Emanuel A Guedes

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Posted 22 December 2008 - 06:42 PM

Hi David,

Have you seen those links up there?

Here is some interesting info related to:

LINK I

LINK II


Any thoughts?

This is another one but quite curious find:


View on Vimeo

Emanuel :-)
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#9 Emanuel A Guedes

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Posted 22 December 2008 - 06:47 PM

But you can also dial it in using ClearScan.

I am not sure if this feature is possible with this camera. I am afraid not.
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#10 Saul Rodgar

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Posted 22 December 2008 - 09:02 PM

The info on the first link Emanuel posted makes me want to repeat my earlier assessment of working with this particular camera: What a pain in the ass.

I can picture myself trying to set the correct exposure on a camera by adjusting the aperture on the lens and then shining light through the lens and immediately hitting the EL button, just to realize it doesn't work for the scene so I have to do it all over again? What if it goes to ASA 400 rather than the desired 200, say? As if things weren't hard enough on set already.

I suppose one could just do once it at the beginning of the scene and hope the battery lasts enough to shoot all the set ups at the same stop (which I always try to do anyway). But still, this really seems to much to deal with on a real life case / scenario. For most hobbyists, this may work, but when one is in the middle of an already hectic shoot, trying to deal with this (even having an assistant do it) could be harrowing to say the least.

Edited by Saul Rodgar, 22 December 2008 - 09:05 PM.

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#11 Chris Gloag

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Posted 28 December 2008 - 01:40 AM

Usually it would be 1/50th for 50 Hz lighting. But you can also dial it in using ClearScan.


Is there ClearScan?
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#12 DJ Joofa

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Posted 28 December 2008 - 03:11 AM

Electricity is a bitch , isn't it?

Three options:

A. Change your camera frame rate to 25 to match PAL land's 50hz power rating.

B. Change PAL land's electric AC interval to 60 hz/ sec to match your camera's 30 fps.


If the digital camera is a rolling shutter one, then, unlike a film camera, framerate has no effect on flicker if exposure time is matched to line frequency. Okay, framerate does have an effect on the phase of the flicker, however, the amplitude of the flicker is controlled by exposure time, and when amplitude is made to go to zero by selecting appropriate exposure times (n/(2 * line frequency), where n = 1, 2, ...) then the dependency on the framerate is removed.
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#13 Chris Gloag

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Posted 28 December 2008 - 04:35 AM

If the digital camera is a rolling shutter one, then, unlike a film camera, framerate has no effect on flicker if exposure time is matched to line frequency. Okay, framerate does have an effect on the phase of the flicker, however, the amplitude of the flicker is controlled by exposure time, and when amplitude is made to go to zero by selecting appropriate exposure times (n/(2 * line frequency), where n = 1, 2, ...) then the dependency on the framerate is removed.

Do you mean we can avoid the flicker just with the shutter speed? Lower than 1/50 second?
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#14 DJ Joofa

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Posted 28 December 2008 - 04:42 AM

Do you mean we can avoid the flicker just with the shutter speed? Lower than 1/50 second?


Yes, for a camera based upon a rolling shutter chip. However, framerate does bound the max. exposure time (shutter speed). For 25fps, max is 1/25 seconds, so exposure times of only 1/100, 2/100=1/50, 3/100, (and perhaps 4/100=1/25 depending upon the implementation) might work.

Edited by DJ Joofa, 28 December 2008 - 04:46 AM.

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#15 Chris Gloag

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Posted 29 December 2008 - 01:12 AM

And 30p for further 24fps conversion?
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#16 DJ Joofa

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Posted 29 December 2008 - 03:34 AM

And 30p for further 24fps conversion?


1/100, 2/100=1/50, 3/100 (though this one is close to 1/30 = 33 milliseconds and depends upon implementation, due to many signal dependent issues including blanking).
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#17 Chris Gloag

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Posted 29 December 2008 - 11:14 AM

Seems 1/50 is anything between two internal parameters, an electronic shutter speed emulation parameter and some kind of darkening parameter, and perhaps the auto program adjusts that latter darkening parameter for fine-tuning but not the internal shutter speed parameter, the actual shutter speed is identical at the reported speeds of 40 and 50. If you shoot mainly on a 50, that will be about 1/45. Do you think as acceptable for avoiding the flicker?
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#18 DJ Joofa

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Posted 29 December 2008 - 11:22 AM

If you shoot mainly on a 50, that will be about 1/45. Do you think as acceptable for avoiding the flicker?


I hope that you don't see any flicker at 1/45. In theory, there should be a little, but in practise you might have to try.
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#19 Chris Gloag

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Posted 29 December 2008 - 10:17 PM

I hope that you don't see any flicker at 1/45. In theory, there should be a little, but in practise you might have to try.


No camera yet. Would you prefer a slower/longer shutter speed? As for instance?
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#20 DJ Joofa

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Posted 30 December 2008 - 01:05 AM

No camera yet. Would you prefer a slower/longer shutter speed? As for instance?


Won't go into motion blurr issues in this post.

A longer shutter speed (exposure time) is good for noise reduction, with the assumption that proper calibration is done for read type of noises such as dark current that becomes more problematic at longer exposure if the scene illumination is low. For regularly illuminated scenes longer exposure times work good for noise reduction.

Another advantage of longer exposure times is that if the exposure time is mismatched to the line frequency, then the (envelope of the) amplitude of flicker decreases with increase in exposure times. Please note that the actual amplitude of flicker is fluctuating but the fluctuation gets lower as exposure time increases as shown below:

Posted Image

In addition to intensity changes between successive frames, flicker also manifests itself as banding in the same single frame, which is easier to detect on uniform intensity areas, as shown below:

Posted Image

As mentioned before the wavy/banding amplitude shown in the image above can be reduced by choosing longer exposure times, and for certain exposure times the amplitudes totally goes away (i.e., converges to a constant > 0, so each image will have a gray cast, but since all frames will have the same cast it will be unnoticeable).

Edited by DJ Joofa, 30 December 2008 - 01:06 AM.

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