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7D owners, help me track a flicker problem

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Stewart Mayer
7D owners, help me track a flicker problem
on Feb 17, 2010 at 6:22:12 pm

Hello fellow 7D owners. I do a lot of timelapse and motion control timelapse shooting with DSLRs and think I have discovered a problem with the 7D when shooting image sequences. It would be great if anyone could test this out, and if i'm right ask canon to fix it (the squeeky wheel gets the grease).

I discovered this while shooting animation backgrounds. I shot raw and jpg simultaneously. when playing back the footage (after turning the sequential stills into video) there was a seemingly random flicker on some frames, sometimes in the jpg only, sometimes in the raw only, and sometimes on both. Some shots did not show it at all. I'm shooting with controlled lighting, all manual settings, and zeiss manual primes with manual iris. On our shoot we had to start using my backup XS and T1i cameras instead of the 7Ds. They worked fine.

The problem (I think) I've deducted is that, being a pro camera the 7D has dual processing chips instead of one, and they process at slightly different luminance levels, maybe the circuit board leads are of different lengths to the different processors' AD converters, who knows. This problem appears intermittent because the 2nd processor is only used when the 1st processor is overloaded, making it appear random.

One way to demonstrate this, and a test i've done on two 7D cameras, is take the exact same photo twice in manual mode, once with live view off, then with live view on, you can then review the photos back to back and see the luminance shift. My theory here is that with live view off, the 1st processor works with the image. With live view on the 1st processor does the live view and the 2nd processor works with the image.

I know this seems strange, but it is the only explanation to what seems like a random luminance shift. If you only shoot JPG image sequences then you've probably never seen this. If anyone can chime in and let me know if i'm totally wrong or right, that would be great. If i'm right then maybe canon could compensate for the shift in firmware.

Thanks,
Stewart


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Jonathan Ziegler
Re: 7D owners, help me track a flicker problem
on Feb 17, 2010 at 7:43:47 pm

Hey there, what are you using to play back the frames on? In other words, you shot on the 7D, then you turned them into video in what app? If you are playing back on the 7D, don't rely on the output, rely on something like Quicktime instead. Also, I would run all the frames through Adobe RAW or Lightroom or something that you can use to ensure you have the exact same levels on each frame and then convert to video from jpegs in Quicktime.

If I'm not getting what you mean, then please clarify. I do time-lapse with my Canon Rebel xt straight to hard drive with the built-in canon remote shooter. Sounds like there are too many factors to lay it on just one thing.

Jonathan Ziegler
http://www.electrictiger.com/
520-360-8293


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Norman Pogson
Re: 7D owners, help me track a flicker problem
on Feb 17, 2010 at 8:36:14 pm

My theory is that what you are seeing is an inconsistent iris in the lens, which is quite normal but does show up as flicker in the film because there is a slight exposure variable. Modern lenese don't have aperture rings, the camera body sends an electrical signal to the lens to stop it down to your selected setting, being electrical you can get fluctuations.

To test why don't you tape over the electrical contact on the lens, or put a fully manual old lens on with an aperture ring and set the aperture to wide open and run a test.

My Canon 7D Blog


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Stewart Mayer
Re: 7D owners, help me track a flicker problem
on Feb 17, 2010 at 8:53:43 pm

I thought that too at first, since my first test that showed it was with an electronic lens. But the rest of the shooting was done with the Zeiss ZF manual lenses that have an old school iris ring and no electronics. They are actually nikon mount but I used an adapter ring.

Rented a set here: http://www.filmstarrentals.com/Zeiss-Lenses-For-Rent-in-Boston

Do you happen to have a 7d? take a photo in manual mode with a manual lens with and without liveview on, the difference will show up every time. Or maybe it is something different? But the exposure difference is the same whether at 1/4sec or 1000th exposure so I dont think it is a faulty shutter either.

hmmmmm



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Stewart Mayer
Re: 7D owners, help me track a flicker problem
on Feb 17, 2010 at 8:36:38 pm

Hi Jonathan, thanks for your input.

I can see the shift directly on the camera, and in premiere pro, and in quickime (after importing sequential stills), and stills batch converted from raw to jpeg in photoshop and brought into premiere and quicktime. I've been through it all, and the actual post gurus who are animating over our backgrounds found it too (actually they found it first as they were checking the shots after each day of shooting). I've been shooting timelapse with DSLRs for a couple years and this is the only camera to exhibit this behavior that i've used, after we determined the 7d was our problem, we switched to the XS and T1i cameras for the remaining 5 days of shooting with exactly the same setup and lenses and it was fine. Do you have a 7D to test with? Any suggestions? I'm willing to try them if someone can think of something I've not tested for yet.

thanks,
stewart



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Jonathan Ziegler
Re: 7D owners, help me track a flicker problem
on Feb 17, 2010 at 9:19:45 pm

I won't have one to play with until Saturday. It sounds like you got it to work, though. I'd talk with Canon about it.

Jonathan Ziegler
http://www.electrictiger.com/
520-360-8293


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Peter DeCrescenzo
Re: 7D owners, help me track a flicker problem
on Feb 18, 2010 at 1:26:46 am

Hi Stewart: Philip Bloom may be getting similar flickering results in his timelapses. He says he's had success using software to correct his footage in post, but I don't know if he's identified the root cause yet:
http://philipbloom.co.uk/2010/01/24/sky/


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Stace Carter
Re: 7D owners, help me track a flicker problem
on Feb 18, 2010 at 2:25:05 pm

I'm not sure if this is what you're talking about, but Canon reccomends covering the eyepiece to prevent light leak when not using Live View (if you won't have your face pressed against it).

There's a little rubber cover that comes on the strap of the 7D (and the new Rebels as I recall) that will snap right on and should prevent any erroneous exposure adjustments.

Cheers,
Stace

Apple Certified Trainer


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Stewart Mayer
Re: 7D owners, help me track a flicker problem
on Feb 18, 2010 at 3:57:53 pm

That is one of the few simple things I had not tried, thank you. Just tried it and it makes no difference unfortunately. But, had it been the problem, I would have had to stick my head in the sand for a month.

I have canon investigating... boy, getting through their phone bank is next to impossible. Also following a few more leads, and emailed phillip bloom to see if he ever solved it. If this gets resolved i'll be sure to post the findings/resolution.

thanks,
stewart



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James Stanek
Re: 7D owners, help me track a flicker problem
on Mar 6, 2010 at 12:42:51 am

I think the flicker you are seeing is not unique to the 7D, but is typical of most DSLRs when used for timelapse or stop motion work. I chased this problem around on several Nikon bodies, and since then, I've seen confirmation in several timelapse oriented website discussion groups. The flickering is caused by the iris. On modern DSLRs and SLRs, you may set the iris manually, but the camera will open it all the way between shots, so you get the brightest viewfinder to see through (and for the autofocus system) while composing. Then, when you press the button to take a picture, the mirror swings up, the camera stops the iris down to the selected f-stop, and the shutter activates.
The problem for stop motion work is that the iris never stops down to the exact same place twice. This error is well within the tolerance of what is needed for still photography, which is what the camera is built for. However, when you play the frames in sequence, your (very sensitive) eye sees this tiny variance in exposure as flicker.
Regardless, it's relatively easy to determine if this is your problem. Make a series of tests at different f-stop settings. The problem should go away when the lens is set to it's maximum aperture. It should get progressively worse as you stop the lens down further towards F/16.
Fixing it is harder. You can shoot wide open all the time, which limits depth of field and generally requires NDs for adjusting exposure time. You can shoot nearly wide open to minimize the problem and live with it. You can try one of the various flicker correction plug-ins. Personally, I haven't had much luck with the plug-ins, but I haven't tried the newer ones. Try checking out some timelapse on DSLR forums for more info. I only periodically skim them myself, so I don't have any particular ones to rec.


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Mathew Joki
Re: 7D owners, hel* me track a flicker problem
on Oct 8, 2011 at 7:54:18 am

Make sure that "Auto Lighting Optimizer" is OFF and "Highlight Tone Priority" is OFF.

See if that helps.


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Helen Foster
Re: 7D owners, hel* me track a flicker problem
on Oct 18, 2014 at 7:11:31 am

I've got a Canon 7D and have been trying to address flickering by eliminating one possible source at a time. I've shot in manual, turned off auto white balance, covered the viewfinder, disengaged the lens contact points etc and am STILL getting flicker.ive been shooting in RAW only. I'm concerned I'm going to wear out my camera trying! However I think I'm missing something, and that there are some in - camera setting on auto that I'm overlooking.


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