A GL-2 Imaging Bug / Attribute - Page 5 at DVinfo.net

Go Back   DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon HDV and DV Camera Systems > Canon XL and GL Series DV Camcorders > Canon GL Series DV Camcorders

Canon GL Series DV Camcorders
Canon GL2, GL1 and PAL versions XM2, XM1.


Reply
 
Thread Tools Search this Thread
Old August 21st, 2003, 03:51 PM   #61
Trustee
 
Join Date: Apr 2002
Location: Auckland, New Zealand
Posts: 1,727
As far as the corners go, that definately looks like the keyhole effect. For the difference in darkness, how far in were you zoomed Ryan? If you zoom in too far with an f-stop 2.4 (I think) or lower you will notice the camera will close down the iris automatically, and hence a larger f-stop and the image will go darker. In auto it might have compensated for this by lowering the shutter speed so the effect might not be as pronounced...Just a guess.

Cheers
Aaron
__________________
My Website
Meat Free Media
Aaron Koolen is offline   Reply With Quote
Old August 21st, 2003, 04:00 PM   #62
Warden
 
Join Date: Mar 2002
Location: Clearwater, FL
Posts: 8,267
You have two effects going on at the same time. Read my post above and you'll know all about vignetting (keyhole effect).

The reason the picture darkens while you zoom in manual is because the lens is a variable aperture lens. You set the exposure (aperture and shutter speed) in manual, but the aperture changes as you zoom (lens design). Depending on how you zoom (wide to tele or vice versa) and set the exposure the picture will become lighter or darker.

Set the exposure to auto when you zoom, or ride the aperture and adjust it as you zoom.
__________________
Jeff Donald
Carpe Diem




Search DVinfo.net for quick answers | Where to Buy? From the best in the business: DVinfo.net sponsors
Jeff Donald is offline   Reply With Quote
Old August 22nd, 2003, 06:20 AM   #63
Regular Crew
 
Join Date: Jan 2003
Location: Chicago, Illinois
Posts: 116
OK, I get that now, but can someone explain why this started happening out of no where? I'm looking at all of my old footage and see no darkening or vignetting going on.
__________________
Ryan Krga
ryankrga773@hotmail.com
Ryan Krga is offline   Reply With Quote
Old August 22nd, 2003, 06:39 AM   #64
Warden
 
Join Date: Mar 2002
Location: Clearwater, FL
Posts: 8,267
In all your old scenes, how often did you shoot a white wall while zooming? In most cases, the vignetting will not be seen in a average outdoor scene. Depending on the lighting, you may or may not notice it occasionally indoors. I suspect it has been there all along and you've just not noticed it.
__________________
Jeff Donald
Carpe Diem




Search DVinfo.net for quick answers | Where to Buy? From the best in the business: DVinfo.net sponsors
Jeff Donald is offline   Reply With Quote
Old August 22nd, 2003, 07:24 AM   #65
Regular Crew
 
Join Date: Jan 2003
Location: Chicago, Illinois
Posts: 116
I just shot the wall to show you what I was talking about, I didn't zoom in on either of those shots. It is VERY noticeable in an outdoor scene as well. It's a pretty big flaw to not notice, it only started happening when I put a Sony Premium tape in my camera.
__________________
Ryan Krga
ryankrga773@hotmail.com
Ryan Krga is offline   Reply With Quote
Old August 22nd, 2003, 07:45 AM   #66
Trustee
 
Join Date: Apr 2002
Location: Auckland, New Zealand
Posts: 1,727
Ryan, this is very strange and I can't offer any other suggestions. What happens if you put the old tapes back in? The tape won't have anything to do with it, but to be sure put other ones in. Hvae you bumped your camera at all recently? I don't know if it's possible to put the lens mechanism out of kilter or not.


Cheers

Aaron
__________________
My Website
Meat Free Media
Aaron Koolen is offline   Reply With Quote
Old August 22nd, 2003, 07:51 AM   #67
Major Player
 
Join Date: Sep 2002
Location: Belgium
Posts: 804
See my post on dec 3 2002
Mireille, just read Ken Tanaka's tread. The "keyhole" (portholing) is known with most (all) zoom lenses on their extreme zoom-in position specifically at wide open aperture. The effect belongs to the mechanical vignetting and is caused by the large entrance pupil (at that extreme zoom setting), which becomes larger than the focussing lens group diameter, causing the "keyhole" effect and the "F drop". I wonder if you will find a XM2 which at low F number will not show this effect. If you do a check, keep in mind that the human eye rapidly adapts to brightness non uniformity. So you should use fast zoom-in/out in manual low F-number setting on a uniform gray field. Did you know that most TV sets have a 50% brightness fall-off towards the corners... ever noticed?
Andre De Clercq is offline   Reply With Quote
Old December 21st, 2003, 09:15 AM   #68
Regular Crew
 
Join Date: Jun 2003
Location: Sydney, Australia
Posts: 125
Zooming and Darkening of Image

Hi Ken,

I just read this thread and I have also noticed that my XM2 seems to darken the image in low lit conditions near the far end of the zoom.... but I think that the manual actually says this on page 78...

"The brightness of the subject may change if you zoom during exposure lock."

I'm not sure if this is a bug or whether this has already been addressed in the many replies (which I haven't had the time to read), but a work around would be to zoom in all the way and observe the f-stops... note what reading is at the end of the zoom and then zoom back to wide and re-adjust your f-stops to the ones that appeared at the "end" of the zoom.

That way when you zoom in there will not be any darkening of the image.

Cheers, and let me know what you think.
Jack
Jack Robertson is offline   Reply With Quote
Old December 21st, 2003, 12:02 PM   #69
Regular Crew
 
Join Date: May 2003
Location: Indianapolis, IN
Posts: 177
Re: Zooming and Darkening of Image

<<<-- Originally posted by Jack Robertson : Hi Ken,
I'm not sure if this is a bug or whether this has already been addressed in the many replies (which I haven't had the time to read), but a work around would be to zoom in all the way and observe the f-stops... note what reading is at the end of the zoom and then zoom back to wide and re-adjust your f-stops to the ones that appeared at the "end" of the zoom.

That way when you zoom in there will not be any darkening of the image.

Cheers, and let me know what you think.
Jack -->>>

Yes, this apeture setting is the key here, and this has been addressed in the repiles you didn't read. Essentially, unevent light falloff is eliminated when the apeture is closed a little from wide open.
Joe Sacher is offline   Reply With Quote
Old November 23rd, 2005, 03:13 PM   #70
New Boot
 
Join Date: Nov 2005
Location: Ljubljana, Slovenia
Posts: 7
Hi, a newbie here!

Using this old thread as I do not want to open a new one about similar problem.

Recently I bought an used XM-1 (GL-1). Today I noticed pretty disturbing light falloff (is is this the correct term?) at the corners, specially when zooming-in and zooming-out.

As far as I read in this thread, this should be something normal to get used to with prosumer camcorders. However, I think that in my case it could be a defect.

I made a clip, capturing white wall while zooming in and out. All settings were manual, 1/60, f/1.6, gain +6.

The room was evenly lit with a 100W tungsten bulb.

Here is link to the clip: http://www.privacyblog.net/IAM/test/vignetting.avi

Could somone please comment this? Is this normal or have I bought a faulty cam?
Ales Marlin is offline   Reply With Quote
Old November 23rd, 2005, 05:56 PM   #71
Wrangler
 
Join Date: Sep 2001
Location: Northern VA
Posts: 4,298
Look to me like it could be normal.

See notes above on zoom. Then you zoom in the maximum lens apreture drops from F/1.6 to something like f/2.6 and in manual exposure mode this will darken the image.

ALL, repeat ALL, lenses have corner fall off, especially noticeable with white (gray) flat surfaces, zoom lenses, and at maximum aperture. Corner fall off can be a stop or even more relative to the center. Usually not noticed with averaage image content.
__________________
dpalomaki@dspalomaki.com
Don Palomaki is offline   Reply With Quote
Old November 24th, 2005, 12:05 PM   #72
Regular Crew
 
Join Date: Aug 2005
Location: Montreal, QC
Posts: 60
I had this problem and changed the camera.... the new one had the same problem. It only happened in an artificially lit room. It was noticeable at wide angle and got worse when zooming in. It didn't happen on my old Panasonic NVDA1, which has 17x optical zoom.

There is a fault, no doubt about it.

However, I kept it beyond the "returnable" date and couldn't change it. Pity... I would have gone for the Sony HDV camera.

Never mind, the pictures in general are very good, I avoid indoor filming with white walls (difficult in the Middle East!!) and am waiting until the thing croaks or my kids wreck it so I can get the Sony!! The XM2 is a good, but overhyped camera as far as I can see.
Geoff Holland is offline   Reply With Quote
Old November 25th, 2005, 02:31 PM   #73
New Boot
 
Join Date: Nov 2005
Location: Ljubljana, Slovenia
Posts: 7
Thank you for replies. I will mainly use the camera outdoors, so if this is mainly an issue when shooting in rooms with white walls under artificial light, it's not such a problem.

Apart from my very busy schedule it is snowing here almost whole week, so I had no opportunity yet to test it outdoors.

Will post a message when I make an extensive test outdoors.
Ales Marlin is offline   Reply With Quote
Old November 25th, 2005, 08:56 PM   #74
Trustee
 
Join Date: Jun 2005
Location: Hollywood, CA
Posts: 1,675
Images: 1
Looking at the output on a 20" production monitor, I'm seeing very, very little change in the image as I zoom into a white wall, however very close to the end of the 20x zoom (perhaps at 19x onwards) the image gets universally darker. The vignetting is very, very barely apparent. I bought my GL2 about four months ago.
__________________
BenWinter.com
Ben Winter is offline   Reply With Quote
Old November 26th, 2005, 10:54 AM   #75
Trustee
 
Join Date: Oct 2001
Location: San Luis Obispo CA
Posts: 1,189
To those new to this discussion...A big component of this "bug" (and it isn't a bug...it's simply the limitation of providing a 20x zoom in a camera at this price point) is the gain settings, in combination with large apertures that would typically be present when one is inside, photographing a white wall. In a typical indoor lighting situation the automatic gain on the gl2 will naturally go to +12db...what gain does in this situation is to expand the tonal range by moving midtones towards the highlight range...essentially increasing the contrast of the tonal range of the scene...so any variation in the white wall, due to fall-off at large apertures, would be magnified by this added gain. (white balancing incandescent or flourescent light sources add to the problem even further). Ben's comment regarding the overall darkening near 20x is correct as the maximum aperture of the gl2 is smaller at the long end of the zoom.

One would probably never see the vignetting effect in an typical daylight situation, and as long as the light levels are high enough in an interior, and you're photographing your kids instead of the drywall texture in your living room, it's likely that you won't see it there either. Oh, and didn't your momma tell you it's bad manners to play with your zoom like that all the time...

Cheers

Barry
Barry Goyette is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon HDV and DV Camera Systems > Canon XL and GL Series DV Camcorders > Canon GL Series DV Camcorders

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 07:08 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network