Black Corners When Using Polarizer Filter on GL2 at DVinfo.net

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Canon GL Series DV Camcorders
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Old January 18th, 2003, 11:06 PM   #1
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Black Corners When Using Polarizer Filter on GL2

I was shooting today in really bright sunlight with only the polarizer and the lens hood on. After bringing in on my PC, it seems that when I zoomed in, the corners of the frame started to fill with a darker image until it made a circle in the middle of the frame and then the black disappeared when I zoomed back out. Anyone seen this problem, hope it's just my polarizer and not the lens. I'm guessing this is called "lens flare"? Is there a larger hood I can get, or do I need to change my position? I tried to shoot with the sun behind me at all times. Unfortunately I can't post a pic of what I'm talking about here. You guys are great and I read ya every day. Thanks for reading,

Mike
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Old January 18th, 2003, 11:41 PM   #2
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What your seeing is the key holing effect, which has been noted on this camera (and others) before. It is the result of the long zoom range and certain aperatures. I know Ken and several others have noted here on the forums. This thread might throw a little more light on the issue.

Jeff
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Old January 20th, 2003, 11:24 AM   #3
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It's strange though, because all of their descriptions of the problem happned in low light, and I was in very bright sunlight, no clouds at noon. I did have my polarizer filter on, but did not have the digital ND on. So does this mean my camera is faulty and I should send for a replacement? Keep in mind this only happened for maybe 5-10 min of footage, but I was constantly changing settings, then it never happened again.

Mike
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Old January 20th, 2003, 11:49 AM   #4
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Michael,
This is a strange problem that, at least in my findings, seems related to using shutter-priority (Tv) mode in low light. As you've probably seen in the other thread I've not been able to induce the effect in aperture-priority (Av) or in Manual mode.

To determine whether or not you should take the trouble to exchange or repair your GL2 I recommend that you take an hour or so to experiment. If you have access to a professional (i.e. full-frame) monitor, connect the camera to it and work through each of the Tv, Av and Manual modes to discover where it occurs for you. (I described my procedure in the other thread.) If you're going to live with this phenomenon it's important that you establish where it occurs on your GL2. It sounds like it might be a bit different on yours, since you report seeing it with brightly lit conditions.

FWIW, this may not be unique to the GL2. In editing some vacation footage shot with a Canon ZR25 (small 1-chipper) last year I noticed a touch of "key-holing" on a very brightly lit outdoor scene. It only lasted a few seconds and was much subtler than what I observed on my original GL2. But this phenomenon may be related to Canon's internal exposure adjustment algorithms and/or their lens designs. Note that I've never observed this problem with my XL1s or its predecessor, the XL1.

Also FWIW, the lens expert at ZGC feels that it's primarily a function of the GL2's lens design (although he had not studied the problem closely).

Good luck!
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Old January 20th, 2003, 01:53 PM   #5
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Mike,

I'm inclined to agree with ken (and zgc) on this, but as you first described things, it sounds more severe (ie vignetting) than the keyholing that has been discussed before...would it be possible for you to put up a still frame for everyone to look at...I'd like to see it for myself.

Barry
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Old January 20th, 2003, 06:40 PM   #6
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I don't have a website, can I email someone either a clip or a frame that can post it? I'm wasn't aware that we could post anything on here.

Mike
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Old January 20th, 2003, 06:47 PM   #7
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Mike,
If you email a sample (full-size) frame to me I can at least tell you if it's the same phenomenon that I observed. Copy Barry while you're at it.
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Old January 20th, 2003, 06:48 PM   #8
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I'll host it. email me

jtdonald@mac.com


I'll host it on my Mac iDisk.

http://homepage.mac.com/jtdonald/FileSharing5.html

Jeff
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Old January 20th, 2003, 06:50 PM   #9
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Better yet, Jeff. That way everyone can see this.
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Old January 21st, 2003, 01:40 AM   #10
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Michael's clip is up. Download it from my link above.

Jeff
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Old January 21st, 2003, 01:50 AM   #11
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Michael,
I'm having a hard time opening your BLAH.mov. QT thinks it's an AVI and can't find the right data in it.

Can you grab just a frame and put it up as a .BMP or .JPG? You can use the Export funtion from the QuickTime Pro player to produce the .BMP directly from a frame of the clip.
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Old January 21st, 2003, 06:29 AM   #12
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Ken,

I emailed you the file and on my disk I just put two files. The one will fix the fix, VLC is a player and should play the new avi file I uploaded.

Jeff
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Old January 21st, 2003, 08:55 AM   #13
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Sorry the clip is so small, but yahoo will only alow 3MB encoded to send in email. If it's too small let me know and I'll bring one into work and then email you another. Does everyone see what I'm talking about? Also on the zoom out there is a nice bright ring that gets bigger and bigger. Keep note that this does not happen all the time, and this was with one Tiffen polarizer on the camera, w/ the ND off. I believe the F stop was 2.6 and I'm not sure of the shutter. I can review the tape if needed for the settings. About 30 minutes after this shot, I went ahead and put my ND3 and the polarizer on, plus my exposure was locked at -2. The footage turned out awesome, and the sky is a beautiful blue. This was a very bright day obviously and around 12PM which generally is one of the worst times to shoot. Thanks for all your help, I've read you guys constantly for the past 4 months and bought a GL2 from Brian at Zotz because of you all. I could not be happier, well, except if I knew what the hell these black corners are :)

Mike
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Old January 21st, 2003, 09:45 AM   #14
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Michael,
Thanks to Jeff's gracious assistance I finally got a chance to see your clip. (The first frame gave me the impression that it was a shot of the Mars ROVER.)

Yes, your "dark corners" is the same as my "key holing". Yours, at least in this clip, is not nearly as severe as what I experienced with my first GL2 and a return or repair is probably not going to produce much, if any, improvement. It seems that this is just a fact of life with this camera.

As I noted above, you would be best served by experimenting carefully with the camera to note where this occurs and how to avoid it.

Enjoy! And thanks, again, to Jeff!
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