Cirino,

If your target is going to be video that plays on TV, then you will most likely never notice this. I shoot video for both TV and computer, but I always do a "TV safe" type of crop to the footage for computer. This is to keep the titles and such from looking stupid because of too much free space all around. I think it is something to be aware of, but not a real problem for me. The Movie Frame mode more than makes up for it over the VX2000 for me.

Those are very interesting results, Joe. Thanks for doing some lab work!

Gee, I can't imagine what some innocent visitor to that page might think it means...

Yeah, my site gets indexed pretty well by Google. If they robot through DV Community, it should be indexed in a month of so. I'll just let them wonder, when they get there. :)

First, let's start calling it by it's right name - Light Fall Off. The reason for this is that as professionals it reflects poorly on us to use improper or confusing names. Does your mechanic call spark plugs "those round sparky things in your engine." Do we call it a lens or "that round glass whatchamacallit on the end of my camera." This will make it easier to diagnose in the future and aid others who may stumble across this issue.

There is nothing Canon can do to fix this optical defect (except resign and manufacture a replacement camera). Light fall off is present in all optical systems. In other words every lens you own and will own for the foreseeable future, will have light fall off.

If you shoot for TV this is a non-issue. It's in the overscan and won't be seen. The GL2 is an NTSC video camera and as such meets requirements for that use. If you design for web or computer it may be an issue and you'll want to minimize it's effect by following my suggestions in the post above. In the tests the fall off is greatly reduced at F2 and probably gone at F2.8 or F4. Make sure not to do your web or computer work at F1.6, use a different F-stop and it's a non-issue.

Thanks Jeff. This clears it up for me. GL2 it is!!


Thanks...

Setting the f-stop to 2.4 fixed the problem completely. Thanks Jeff.

Jeff, many thanks from another new boot. I was ready to freak out about this issue, but your quick f-stop edjumication saved the day. Back in love with my GL2! And thanks also Joe for posting the examples above.

When I first got my GL2 this problem never occured until now. My waruntee is over and I don't know how to approach the problem. In every post within this topic I seem to find nothing that will fix the problem. When I zoom in about halfway there isn't a keyhole effect, the whole picture darkens! Most of my work is web oriented and I would hate to have to live with this problem or use different settings that I don't want to use on my GL2 just to get rid of the problem. Any suggestions?

Thank you very much.

When the whole picture darkens, is the exposure in auto or manual? Try to duplicate the effect in auto and see if it goes away.

This still was taken in full manual(S - 1/60, F - 1.6, DB - 0).

http://www.visital.com/keyhole/(Unknown) - Still 001.jpg

This still was taken in full auto.

http://www.visital.com/keyhole/(Unknown) - Still 002.jpg

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

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.

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.

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.

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, 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

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?

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

<<<-- 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.

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?

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.

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.

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.

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.

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