Vignetting/Keyhole-ing/"light roll off" revisited at DVinfo.net

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Old March 16th, 2004, 01:09 PM   #1
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Vignetting/Keyhole-ing/"light roll off" revisted

Just shot my first real video with my new GL2. While watching the DVD I created, I noticed the darkening around the corners! (I guess it is commonly called vignetting or keyhole-ing)

I was shooting F1.6 in Av mode, with varying zoom. The light roll off is more noticeable at the longer focal lengths (telephoto).

This really seems like a defect to me. Do all GL2s do this? Can I return the camera?

Thanks,
Ming
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Old March 16th, 2004, 01:57 PM   #2
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Read this thread. All the answers are there.
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Old March 16th, 2004, 03:20 PM   #3
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Ming, if you slog your way through the thread Jeff pointed you to, be sure to read the post from Andre de Clercq, who correctly identifies the problem as "portholing." Andre also explains the cause of the portholing effect, which is common to most lenses.

A couple of weeks ago I shot a comedy concert (George Lopez) for Showtime, and my Sony studio camera had a Canon 100:1 lens. That's 9.3mm to 930mm. When we were setting up, I checked out the lens, and zoomed full tight into a Sprite bottle on the stage over 200 feet from my camera position, and guess what? Portholing. And the camera wasn't even wide open, at f/2.8. And this from a lens that costs over $200,000.00!

Sony hides the portholing effect on the PD150/VX2K by forcing the lens to stop down as the focal length reaches the long end of the zoom range. You cannot shoot full tight at f/1.6 with a PD150/VX2K. The camera will change the stop to f/2.4 (if I remember right) automatically, even if you are in manual mode.

And I know Jeff will appreciate me clearing up the confusion between "portholing" and "keyholing." (Actually, keyholing is a technique used for shooting motel videos. Wink.)
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Old March 16th, 2004, 04:01 PM   #4
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Indeed, when I started that thread this optical phenomenon was new to me. I didn't know whether or not I was observing a defect. As the thread progressed it was evident that I was observing a phenomenon of physics rather than a defect.

"Portholing" seems a more accurate label than "keyholing".

Hmm, I wonder if we should call aberrations in zoom servo speed control "potholing"?
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