Specks on screen at low shutter speed. at DVinfo.net

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


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Old January 27th, 2005, 10:19 AM   #1
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Specks on screen at low shutter speed.

I know this will sound pathetic, but for all those who like things perfect, Im sure you will bear with me.

Have just purchased an XM2, and its wonderfull.

However, have noticed that, when shooting at a very low shutter speed (ie - 1/25, 1/6) - say, at night time to brighten image (havent got a video light yet), have noticed about 3 or 4 minute white specks. (I must point out that I only see this when played back on my widescreen TV).
I've cleaned the lens with a lintfree cloth, but to no avail (unless of course its behind the camera lens.... :-(

Most people say im just being pathetic, and cant notice it untill i point them out and.....well, they are right, i prpbably am being pathetic !!

But was just wondering whether anyone knows if this is because of the lower shutter speed (ie - it loses resolution, causing these little buggers) or something).

Have a go - see if you get the same result....

Have not noticed anything during normal auto mode, but its just a niggling little thing.......

Cheers,
Richard.

ps - 1st post, sorry it sounds just a whinge.....
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Old January 27th, 2005, 03:31 PM   #2
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Richard,

Probably not the answer you want to hear, but....I have an old Panasonic VHS full size camcorder with the same issue. Specks at standard shutter speed, no specks at high speed shutter. You are likely seeing a couple of defective pixels in the ccd. They are stuck partially on such that it takes very little light for them to turn full on.

Dirt on a lense would never show up as white specks because it's blocking the light entering the lense at that point and will be dark specks. The higher shutter speed keeps those pixels from being on long enough to go into saturation.

If this is a new camera, send it in for service. Although a few dead pixels in the LCD or VF are deemed acceptable by camera manufacturers, defective CCD pixels are not.

good luck,

=gb=
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Old January 28th, 2005, 07:31 AM   #3
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Thanks Greg !

Contacted Jessops this morning (where I purchased unit), and explained situation (and included the fact that I'd contacted an 'expert' in camera's, who concluded that it was probably dead pixcels on the CCD :-)

I think, though im not convinced till they do, that they will exchange camera for another on, so fingers crossed.

Tried it again last night, and the specks were there, even with everything auto..... so long as im aiming at a black background. I wondered whether it might be a couple of specks behind the lens itself. When zooming, the specks do not move.

My missus thinks im sad, but you know what its like - I'll be forever looking for the specks.

Many Thanks for your comments, I think they have just bagged me an exchange (I hope).

Richard.
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Old January 28th, 2005, 10:28 AM   #4
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Taking the front of the xm2 off ??

Following on from this, Jessops now say it will take upto 3 weeks to get one into the coutry (think they are hoping I walk away).

Was wondering if anyone has tried taking the front of their xm2 off, in case behind of the lens needed a clean.
I dont personally fancy this, as it probably invalidates any warrenty, and also I dont want to do any damage....

Any advice.....
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Old January 28th, 2005, 11:04 AM   #5
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Before attempting any disassbly cleaning, (which you really shouldn't do at all) you should look at this video on a computer and view one color channel at a time.

If you notice the same white spec in all three channels, the issue is likely in the optics somewhere. Perhaps of speck of dust is reflecting some stray light from an angle. This is very unlikely for what you are describing.

More likely, you have a build-up of "dark-current" noise in a few pixels on one or more of the 3 CCDs. The very nature of silicon CCD electronics creates some electric charge (noise). For short shutter speeds, the CCD is read & cleaned before this even has much of a chance to buildup. Low temperatures also reduce this effect. Longer shutter speeds, however, allow this charge to build up over time.

What you're seeing may not "technically" be a defect, but simply a characteristic of how the CCD's performs. Most video CCD specs include an allowance for a number of pixels to exhibit this behavior. It's simply the state of the art of CCD manufacturing. A single batch of of thousands of hundreds of CCDs coming of a production run may only have 1 or 2 that are perfect or near perfect. These chips end up selling for $1000's and are installed in scientific-grade/industrial cameras (some of these are cooled with liquid nitrogen to combat remaining dark current noise).
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Old January 28th, 2005, 07:37 PM   #6
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The issue is 'hot' pixels that have a high dark current. This is only noticed when gain is max, or low shutter speeds, usuallly in dark scenes with dark backgrounds taht make the hot pixel noticeable.

There is a note about this in the NTSC GL1 manual, there may be a similar note in the PAL manuals.
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