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Canon GL Series DV Camcorders
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Old August 5th, 2002, 08:38 PM   #1
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GL-2 Flicker Problem?

Looking for suggestions on this situation. When mounting the GL-2 on a moving vehicle, almost all scenes have a slight dark flicker. The frames are about 10-30% darker than normal and happen several times a second- but not in any regular sequence. The set-up is frame mode, manual, 1/30th, ND filter ON, at f/6.3 or higher, manual focus. Doesn't seem to matter whether the vehicle is moving at 20mph or 60mph- the flicker is still there. The camera is cushioned safely in a Cinekinetic mini-saddle although by nature, there is still alot of vibration. Any stationary scenes, whether handheld or tripod, do not have this problem.

We have successfully shot this same set-up with the XL1 and no problems.

Suggestions?
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Old August 5th, 2002, 09:12 PM   #2
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Sounds to me like Frame Movie mode is the culprit. In my experience, Frame Movie mode works best on a stationary, locked-down camera with as little movement as possible. Pans and tilts should be performed slowly, "cinema style." Try shooting in normal movie mode with a shutter speed of 1/60. Anybody else?
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Old August 6th, 2002, 12:21 AM   #3
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I know this flicker, and it isnt the frame mode jitteryness that I think chris is alluding to. I noticed it first when I mounted my gl1 on a steadicam, an everything I tried to isolate as a cause turned out inconclusive...it only happens occasionally, typically 1 to 2 frames that are 20-30 % darker than the surrounding footage...it seems to happen most for me when the camera moves from a darker area to a lighter, contrastier one... even when every control is set to manual. The only time I've seen in pulse relatively consistently is in the video link below. It does occur when handheld, but seems more prevalant on the steadicam for some reason...which is weird. I was just preparing to send my gl1 in for to see if canon knows what it is...

Here's an example of it in a little steadicam piece I thru together a few months back...it happens in two shots near the beginning of the "running" sequence, and another couple clips toward the end...but as you can see...many shots with the same amount of movement have no problems at all....

http://homepage.mac.com/barrygoyette/iMovieTheater4.html

I haven't seen this problem with my gl2...but I'm going to put it through the paces to see if I can make it happen. I'll let you know.

Barry
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Old August 6th, 2002, 07:26 AM   #4
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Barry, didn't your mother tell you not to run with your camera? My best guess is the motion, even on the steadicam, is causing the aperature to open and close slightly. The aperature bounce is causing the strobbing effect. The opening and closing is usually controlled by 1 or 2 springs. I've seen similar effects in 35mm cameras when the springs wear. The springs could need adjustment, replacement or this could be what happens when the GL is subjected to forces the designers didn't anticipate.

Jeff
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Old August 6th, 2002, 09:20 AM   #5
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Jeff

What's wierd about it is that it happens so sporadically, and if anything, a little less when I'm handholding. I did some testing with the steadicam around the yard awhile back, and bouncing the camera didn't do anything...the only way I could get it to repeat (somewhat) was when I moved the camera slowly from under a tree and pointed it on a shadow pattern on a white wall (camera settings all at manual). I just reviewed some footage from when I first got the gl1 severl years ago, and it is there as well...back then I just thought it was the auto exposure system adjusting.

It does seem to have something to do with movement...but it almost seems like the camera is reacting to some stimulus in the image...which makes no sense to me.

Barry
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Old August 6th, 2002, 12:46 PM   #6
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Let me see if I understand this. Both the aperature and shutter are in manual. What shutter speed are you using? Is the Image Stabilization on? Is the frame mode turned on? Are you using auto focus or manual focus? Depending on your answers it could be in the exposure system, AF system, Zoom servo, or a mechanical abnormality.

Jeff
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Old August 6th, 2002, 12:57 PM   #7
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I've run it through every conceivable combo of automatic and manual exposure, focus, image stabilization, all with pretty much the same results...one thing I'm not sure about is white balance...although I think I checked it too...I'll try again to confirm..

Barry
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Old August 6th, 2002, 01:14 PM   #8
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White balance could be a good suspect. Moving the camera from shade to sunlight would trigger the auto tracing white balance. During the WB adjustment exposure could be affected. Your camera under the tree example could be the clue.

Jeff
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Old August 6th, 2002, 02:47 PM   #9
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More information from Ron

Hi folks,

Thanks so much for all the ideas- I will continue to research. For clarification, Image Stabilization is ON and white balance is set to DAYLIGHT and manual focus is essentialy set for infinity.

Ron
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Old August 7th, 2002, 02:03 PM   #10
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I just went and tested my gl1 again on the steadicam, and the problem occured both with the white balance on auto, and with the daylight preset, with everything else set to manual again with no rhyme or reason as to why...

Here's another thought, For me, it only does seem to happen at the brightest situations, outdoors, bright sun. ND filter on...Now with the gl1, that means I'm at f8 or 11..the smallest aperture...wonder if there is anything in that....either with the nD filter, or a looseness in the aperture blades that is more noticeable at smaller fstops...I'm grasping here...

I'm about ready for a call to canon...and I will put the Gl2 through the same test this afternoon.

Barry Goyette
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Old August 7th, 2002, 03:47 PM   #11
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I wonder if it over shoots the aperature it wants, say F8, and goes to F9, and then corrects to F7 then corrects again to F8. This would give you the strobing effect. Compounding this would be the movement of the camera. The scene is changing, therefore the exposure is changing, so it misses the aperature by overshooting, then over correcting. Does the aperature and shutter speed show in the viewfinder on the GL1? What are they set to?

Jeff
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Old August 7th, 2002, 04:09 PM   #12
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Well, the exposure is set to manual, so it really shouldn't be correcting for anything. When it happens on my gl1, it is usually one or two quick flickers, and when I look frame by frame through the footage, it is one frame about 20 percent darker than normal followed by one about half as dark and then back to normal...and there doesn't seem to be ANY correlation to how much the camera is moving, or what it's pointed at (to debunk the theory of my first posting). I have yet to see it do it in low or moderate lighting, but that is the only consistent variable...I ran a few more tests this afternoon on a hunch, I'll take a look at them tonite and report back tomorrow.

still scratching my head.

Barry
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Old August 8th, 2002, 01:22 PM   #13
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Ron

I completed a whole battery of tests yesterday with my gl1, and was unable to isolate the source of the flicker...the only unifying factor seems to be that the camera is moving when it happens, but not in response to any specific type of movement. I'll try out the gl2 today, but I'm thinking that there is something electronicly amiss in my gl1, and probably your gl2 as well. Can you see the flicker on the lcd screen? ...because I can't, it only seems to show up on recorded tape. (this may be difficult to tell in bright daylight)

Barry
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Old August 9th, 2002, 05:50 AM   #14
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Ron

I tested my gl2 today, and found no problem like the one you reported, (or like what I experienced with my gl1). My plan is to give canon a call, and get mine in for repair. I'd reccomend you do the same...At least yours is under warrantee.

Good luck. Let us all know how your problem is resolved.

Barry
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