John, I was referring to the record heads in my video cameras and just wondering how often they should be cleaned. I'm not seeing fully distorted images that would suggest cleaning is mandatory -- just occasional shearing in small parts of images and I'm not sure if that's happening because of accumuled dirt on the heads or some other reason...

I notice some shearing of images when panning and wonder if the record heads in both cameras need cleaning.That sure doesn't sound like anything to do with the heads, but I guess I'd have to see a few seconds of the problem to know for sure. I own the FX1, and the few times I've seen tape problems (caused by a dropout on the tape, and not the head) the picture breaks up for the duration of the remainder of the GOP, i.e., for between 1-15 frames. There is no "shearing" or any other such thing. Instead, you get dots, blocks, and junk.

I have seen actual head clogs on my older DV camera, and they usually look like three or four large horizontal bands of distorted video, with the alternate bands of video looking just fine.

Unless you really know for sure that you've got a head clog, I'd recommend leaving the heads alone.

The manuals for both the FX1 and FX1000 both show examples of dirty heads but that's not what I'm seeing. It just may be it's the camera technology. I was watching a video clip online of the Japan disaster and noticed the same kind of shearing (distortion) when the camera panned across the scene.

Thanks for your reply.

Don, if you could post a short sample of what you're seeing, it may help get a better answer.

Mike

Mike, thanks for your suggestion. How do I attach a short clip to a note here or is there somewhere else to upload to?

Don, put it up on YouTube or Vimeo and give us the link.
edit: Here's another suggestion for you to try (thanks to Danny Hays on the Cow for the tip).
There's a website that gives you 50 gig of free storage, and after you upload a video, you can set it as share. Then you can email anyone a link to download it.

http://www.adrive.com/


Mike

This is nothing to do with the heads at all. It's entirely to do with the mechanics of how the image is scanned on the image sensor chip.

This problem was first noticed with early focal plane shutters at high speeds. Since the shutter itself couldn't be made to move extremely fast, the solution was to start closing the upper shutter before the lower one had completely opened. This meant the image was exposed in a narrow band that moved from the bottom of the frame to the top. If the scene or object was moving horizontally fast enough, then it wouldn't be in the same position at the end of the exposure that it was at the beginning and you'd end up with horizontal sheer.

The same thing can happen with electronic image sensors when the "shutter speed" is set very high. The sensor can't be read instantaneously so there is a very short delay between when the top scan line is read until the bottom one is. Once again, any fast horizontal movement leaves the subject in a different position at the end than at the beginning.

A slower shutter speed can help minimize the shearing but will also result in more blur. The better solution is to spend huge amounts of money to get a camera with a sensor designed for ultra-high speed capturing. Well ... that may be a better solution for those who can afford it. My wallet certainly couldn't.

Don,
This a known property of camcorders that use CMOS sensors. I am surprised if it's also happening on the FX1 which uses CCDs.
Tom

Without seeing a sample, it's hard to diagnose. He could simply be seeing interlace artifacts from panning too fast.

To answer the OP's other question of how often to use cleaning tapes...

Ideally, never.

The cleaning tape is like sandpaper to the heads so any use of the cleaning tape hurts the heads and should be used only as a last resort.

Head cleaning removes the gunk in the tiny gap in the heads. Using different brands of tapes *can* encourage the accumulation of this gunk, and generally people who do use whatever brand of tape that Wal-Mart has on sale this week tend to experience dropped data (not to be confused with dropped frames - an entirely different problem). The overwhelming volume of anecdotal data supports this, but there's always a couple of people who extrapolate their own good luck into the industry as a whole.

Your camera manual will have something on this, but in the case of my PD-150, it's 100-hours. I have run over 400 Sony tapes through my PD-150 and have yet to experience any data drops and not even opened the cleaning tape cellophane.

Steve Mann

Many thanks to all for your input.

The detailed explanation from chienworks was particularly helpful. I also checked with Sony tech support but the agent wasn't very knowledgable although he did say that head cleaning once every six months was OK. There are a lot of different opinions about head cleaning but after reviewing all the input, I feel cleaning should only be done when absolutely necessary. Going forward, I'll focus on slowing down pans to minimize the horizantal shearing problem.

Again, thanks to all for your excellent replys!

Ah, I think when you're saying "shearing" you mean "rolling shutter?" I've seen a lot of that in Japan earthquake footage too (lots of people out there with DSLR's (with CMOS sensors) taking video of events.

Here's an excellent example of rolling shutter...is this what you're talking about?


If so, the FX1 has a CCD sensor so it should be immune to the effect, but the FX1000 with its CMOS sensor might be prone to the effect (though my gut reaction is that a 3 sensor camera should be relatively immune, if just for the price point).

That said, if that's NOT the problem, ignore me. If you think this is the problem, then, as far as I'm aware, software is the only option to correct it (I believe NewBlueFX has a plugin for that).

~A

I looked at the YouTube clip but that's not the problem I was referring to. I do, however, see the rolling shutter problem with my FX1000, especially when shooting weddings inside with cameras flashing all around. But the shearing I'm referring to is a horizontal distortion that I think was addressed in the reply from chienworks (above).

Anyway, I'll take a look at what NewBlue has to offer, and thanks for your comments.

Well it was either rolling shutter, interlace combing, or something else. But I hope you find a solution either way. Can you post a video of the problem on youtube or somewhere?

I've posted a short clip to YouTube at:

The interesting thing is that I don't see the shearing as much in the posted .avi file but when playing the clip in Vegas, I see the shearing, and it seems to vary each time I play it. Sometimes there's no shearing evident at all. So I wonder if what I'm seeing has something to do with Vegas and not the clip as recorded in my camera???

Don,

I don't see any "shearing" in that clip you posted. Maybe line twitter in spots and some judder when panning.

I don't believe there is a video term called image "shearing". I think you mean image "tearing" where along a "fault line" the image separates momentarily then comes back together.

That is usually caused by poor vertical sync between the display and what it is being fed. It is most noticeable in objects moving horizontally (panning). If you are noticing it on a computer monitor see if you can increase the vertical refresh rate of the video card using it's control panel or the one in Windows. With LCD monitors that is sometimes difficult to do because of limitations.
If you can output the video to an external CRT monitor, I think you may see it disappear especially if you render a loop and play it.

John