SD versus HDV for focus in motion?? at DVinfo.net

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Sony HVR-Z1 / HDR-FX1
Pro and consumer versions of this Sony 3-CCD HDV camcorder.


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Old April 30th, 2006, 03:02 PM   #1
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SD versus HDV for focus in motion??

I have noticed while reviewing others video samples that the sony hd's tend to lose focus on moving opbjects and or panning across ground etc. more than the sd camcorders do. is just me or is this really happening. even things such as painted walls seem to vary in consistancy with the hds as a movement of the camera occurs. the sd's seem to hold the focus better in the same situations and recover faster when refocus is necesarry. any comments and observations on this would be appreciated as I am making camcorder purchase decisions very shortly.
thx
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Old April 30th, 2006, 03:04 PM   #2
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let me expound a bit more on it

on still objects the hd is totally clearer , but I am refering specifically to a moving object or a moving camera, that is when the sd's seem to beat the hds and actually have a clear picture un till the hd regains focus.
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Old April 30th, 2006, 04:08 PM   #3
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I think the focus issue is more a function of resolution, than the workings of autofocus. Something slightly out of focus in SD will be masked by lack of resolution. Something slightly out of focus in HDV will stick out more.
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Old April 30th, 2006, 05:12 PM   #4
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that makes some sense

I guess it could be user ability also, knowing your camera well. can the fx1 be viewed on any hdtv and computer? assuming you are playing it from your hard drive or from the camcorder itself. (refering to hd)
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Old May 2nd, 2006, 01:30 PM   #5
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Hey John,

It depends on how you shoot with the cam. I'm thinking the samples you saw were shot using auto-focus which you never want to use for critical shooting in HD. As Chris said, you are either in focus or out of focus with the FX1. Another factor is what screen you use to focus with. I've found the viewfinder much better for critical focus while tracking a moving person of object. The flip-out LCD screen is sharp but not quite sharp enough for razor sharp focussing in my opinion.

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Old May 2nd, 2006, 01:46 PM   #6
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(John:

You really don't specify what you mean by shooting "in motion". If you are doing a scene shoot in which you have a lot of control, but the actors or center of focus moves from one mark to another, you can critical focus at two points using the scene transition function.

As far as things like sporting events where you are not sure where you point of focus is going to be at any moment, you can't set camera at wide, and have a pretty deep depth of field. However, for teleshots, I think you have to ( 1.) do a zone focus on the area using the push auto focus assist button, or 2) try to follow focus with focus ring, (tough for me, at least) or try to live with (3.) auto focus. I think in a constinuous motion situation, number 1 is best way to go.
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Old May 2nd, 2006, 02:07 PM   #7
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thx for all of the input

sounds like there is still hope for the fx1 in motion shots
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Old May 2nd, 2006, 02:27 PM   #8
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Pans

My experience with the Z1/FX1 is there is some blurring with a pan. But...unless I am panning following the motion of something...a runner...car, etc. But by and large, pans don't work for me so it is not a big issue. I will do short pans and that works fine. The technical end has been pretty well covered on this thread. If all else fails when in manual focus, hold down the "Push Auto" button
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Old May 4th, 2006, 06:23 AM   #9
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At what stage and on what equipment are you seing this additional blurring.

I can't say I've noticed it much and I've shot HDV with the Z1 which is then watched back on a Computer monitor at better that 720p resolution and I haven't noticed additional blurring on reasonable pans other than naturally introduced motion blur, which is obviously there in SD too.
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Old May 4th, 2006, 06:47 AM   #10
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i saw some highway fottage

I saw some highway grabs from fx1 and no blur. I guess my concerns are being put to rest. im glad thx
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Old May 31st, 2006, 11:17 AM   #11
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Keep one major thing in mind--even if something shot on DV/SD is slightly out of focus, no one will really notice (a little better than 350,000 pixels). But in HD, slightly out of focus will scream to people, "out of focus!" (Between 1 and 1.5 megapixels--you see a lot of flaws in the image, if they're present.)

Use the focus assists on the HDV cameras to help out.

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Old August 28th, 2006, 04:30 PM   #12
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GOP Format Causes Blur

Sony's HDV format relies upon a Group of Pictures (GOP) format for encoding data to tape. To allow HDV format to fit onto tape the compression format relies upon a "key" frame (called the I frame) and over the next 15 frames creates a series of bidirectional ("B") frames and data ("D") frames.

Using the key frame as a start the next several frames compares the original image to the next frame image and stores only the differences between the frames, compressing the information to fit on the tape. This process works well enough for non-moving images but can break down with rapidly changing backgrounds.

Tape a rapidly moving water sequence and you'll see artifacts and other problems if you look carefully. These will NOT be visible on the LCD screen on most camcorders, or even on SD monitors. It is an inherent part of the HDV process and cannot be overcome.

Sony has a white paper discribing this process more fully on their website. It is worth the read.
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Old August 28th, 2006, 07:31 PM   #13
 
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All mpeg formats use GOP sequences, not just Sony.
The sequence is IBBPBBPBBPBBI, for example, in a 12 GOP (JVC's 60p format @ 19Mbps)
It might be IPIPIP. It depends on the encoding design and bitrate.

B & P frames are backwards and forwards (bidirectional) predictive, relying on information from the preceding and postceding frames. That said, it's a common misunderstanding that the DCT (B&P) frames cannot act as "I" frames. If the scene changes substantially enough, then any DCT frame can act like an I frame known by another name. If the scene changes significantly enough, the image can become slightly softer as a result of the allocation.
with regards to water, I suppose this can be an issue, but having shot a lot of water at various degrees of angle and sunlight, it hasn't been an issue. HDCAM certainly looks better, but that's also a larger imager and substantially sweeter lens.

One thing to be certain of when comparing images;
Be sure the monitor isn't scaling the image. Otherwise, you don't know what is actual and what is modified, regardless of which camcorder's footage you're viewing. For example, viewing 720p footage on a 1024 x 768 monitor might leave the image with less than optimal, but still fairly accurate representation, but the 1080i footage may appear terrible or wonderful, depending on the scaling ability of the monitor or vid card.
HDV Rack presents weak images from my HD100 if my monitor is at 1600, and good 1080 images at same resolution. And vice versa if I lower my resolution on my laptop (sure wish I had 1900 x 1200 on my laptop).
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Old August 28th, 2006, 10:34 PM   #14
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I'd like to point out that some of our own DVInfo wranglers were involved in a low cost HD shootout a little while back, the Texas Shootout. Adam Wilt was present and wrote an article about it. They discuss stuff like how the cameras handled a rock (or something along those lines) being thrown into water.

http://dv.com/features/features_item...leId=189500064

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