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Old May 25th, 2003, 11:23 AM   #1
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Interlacing during autofocus

I've had my DVX100 for about a week now and I'm noticing that while the autofocus is active the image has some kind of field interlacing weirdness. Once the autofocus locks on, the image becomes clean. It's kind of subtle, but almost looks like the fields become reversed or something. I'm certain that there must be something wrong with my camera.
Has anyone else had this issue?

Thanks,
Brent
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Old May 26th, 2003, 08:12 AM   #2
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from teh sounds of it, your running it in 60/50i which interlaces, as the dvx only runs its progressive modes in full manual operations id say that whatyour seeing is normal...
maybe your shutter is too wide so it stands out a lil more...??

some others whove used this cam more that i might be able to help
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Old May 26th, 2003, 09:36 AM   #3
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Thanks for the reply.
Yes, I am seeing this in 60i mode but what I'm seeing isn't field jitter based on camera motion. It does this even when the camera is locked down and completely still, but only when the autofocus is active.

-Brent
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Old May 26th, 2003, 10:41 AM   #4
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Are you running OIS?
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Old May 26th, 2003, 11:15 AM   #5
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It behaves the same with OIS on or off.
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Old May 26th, 2003, 02:19 PM   #6
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Any chance of you posting a screen grab, or better yet, a short clip (full rez avi)?
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Old May 26th, 2003, 07:49 PM   #7
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I've posted a 1.6mb DivX avi of an example of what's going on to http://home.earthlink.net/~bfeeman/Autofocus_EdgeArtifacts.avi


It's not the prettiest image, but it clearly shows what's going on. If you look at the bright strip running along the center of the frame you can see that it's "buzzing" until the autofocus stops searching. If you turn up the sound you'll hear the whirring of the autofocus- when the sound stops, so does the edge interlacing.

Another example...
http://home.earthlink.net/~bfeeman/Autofocus_EdgeArtifacts2.avi
Look closely at the bright edge of the martini shaker. You can see the buzzing along with the sound of the autofocus. It never locks focus since the object was too close, but it's shows what's going on.

-Brent
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Old May 26th, 2003, 08:03 PM   #8
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It seems like normal aliasing to me. It is common along edges at an angle and where there is a high transient (change from light to dark). I can't comment on the audio. The level is very low, could be the playback on my PowerBook.
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Old May 26th, 2003, 08:05 PM   #9
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Why do you suppose it would suddenly change from a jittered edge to clean edge at the exact moment when the autofocus stops searching? That is what perplexes me.

The edge buzzing is much more noticeable on an NTSC monitor.
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Old May 26th, 2003, 08:06 PM   #10
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The audio is low on my machine as well.

From here, it does look like normal interlacing. But I've shot almost nothing 60i and thus never used the autofocus on the cam, so I may not be the best judge.

What menu settings for gamma, detail, etc. are you using?
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Old May 26th, 2003, 08:08 PM   #11
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I'm using the default F1 settings.
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Old May 26th, 2003, 08:12 PM   #12
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Try changing detail and thick/thin settings and see if it has any effect.

I've noticed that scenes with clipping in whites, which yours appears to have cause artifacts in the cinegamma 24p modes, but not sure about F1.
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Old May 26th, 2003, 09:00 PM   #13
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I tried playing with detail and thick/thin and still got the same results.

Here's one more example to show what's going on.
http://home.earthlink.net/~bfeeman/A...Artifacts3.avi


I did an autofocus and a manual focus to compare the edge detail.
Like I said, it's really noticeable on an NTSC monitor but in this example you can see the difference between the two focusing methods.

I'm also not convinced that the noise I'm hearing during AF is normal.

I really appreciate everyone's help on this.
-Brent
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Old May 26th, 2003, 09:12 PM   #14
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Here is an image that compares what the problem is during AF, and what the image should look like. Neither of these frames have motion in them- the interlacing in the first image is caused by the AF.


http://home.earthlink.net/~bfeeman/AF_Artifacts.jpg

-Brent
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Old May 26th, 2003, 10:55 PM   #15
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Yeah, the AF artifacts image is compelling. If the detail, thick/thin has no effect - it does sound like you might want to have the camera looked at.

I have not heard other 60i shooters talk about autofocus or noise that I can recall on since the cam was out.

My hunch is if menu settings (gamma, detail etc.) do not effect the artifact and it's visible on monitor connected directly to the camera, on LCD and in NLE, then you have a compelling case to get the cam fixed.
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