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Sony HVR-Z7 / HVR-S270
Handheld and shoulder mount versions of this Sony 3-CMOS HDV camcorder.


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Old March 1st, 2008, 06:51 PM   #1
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24P Jerkyness?

HD newbe here, so beware! ;-)

My Z7U, when set for 24P, even the slowest pan is jerky. Any movement, even with the camera stationary, a person walking slowly looks jerky. Perfectly smooth at 1080i.

I can't believe what I'm seeing would be acceptable--film doesn't look like this to me.

What am I missing? A setting or . . . ?

Thanks!
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Old March 1st, 2008, 08:33 PM   #2
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It may be the on-camera display. Try connecting it to a monitor. If the problem persists, maybe you could post a clip.
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Old March 2nd, 2008, 12:18 AM   #3
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24p is jerky, even with the best film cameras. That's why you see all those dolly tracks on any film shoot.

When you shoot 24p you have to really watch your movement and rarely zoom if at all. None of this is unique to the Z7. That's just the way it is with any 24p.
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Old March 2nd, 2008, 12:44 AM   #4
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The reason is because of the way our brains interpret image sequences. If we see too much movement between 2 frames our brain sees to separate images, where as if you have a sequence of oh, I don't know, say 24 images every second :), where it the difference between each frame is within acceptable limits then your brain fills in the gaps and makes the motion smooth ( same thing with 30P and 60i but it's less problematic because there are more frames there so the difference between each one is less and your brain is much less likely to discern each frame separately. ( wow that was a run on sentence :P ).

I'd highly suggest you do a little studying on filming techniques if you want to continue to use 24p as it has some rules ( well, maybe not so much rules as ... guidelines ) such as not panning something across the screen faster than 7 seconds (depending on screen aspect ratio or SAR for short) among others.

24p is actually just a standard that was arrived at because it was the cheapest frame rate that most motion appeared smooth at.

Anywho, just a little FYI there I guess.

Dave
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Old March 2nd, 2008, 01:07 AM   #5
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It is due to the 2-3 pull down.
Z7U records the 24p image over 60i through the 2-3 pull down process.

FYI, film flashes twice a frame. It means there are 48 flashes per second.
It looks smooth compared to the digital 24p.
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Old March 2nd, 2008, 01:33 AM   #6
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Quote:
Originally Posted by Kenny Pai View Post
It is due to the 2-3 pull down.
Z7U records the 24p image over 60i through the 2-3 pull down process.

FYI, film flashes twice a frame. It means there are 48 flashes per second.
It looks smooth compared to the digital 24p.
Thanks, I didn't know that :)

Always happy when I learn something new, any other knowledge tidbits you care to share ? :)

dave
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Old March 2nd, 2008, 06:23 AM   #7
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Great Info, But . . .

This info is VERY helpful, but leads to more questions.

The jerkyness I'm seeing seems like makes 24p unusable. Even with my Z7 is on a tripod as is not panning or moving at all, a person on the screen moves his arm to pick up a drink of water, looks annoyingly jerky. How can film filmmakers be excited about 24p video cams for making movies? It looks awful to me. I've tried with a small monitor and my 52 inch 1080P LCD, the jerkiness is bad. And, these days the fashion is that something has to be moving at all times--preferably the cam is always panning or something.

If film is 24 frames but is delivered to the screen 48 times per second and 24P video is delivered only 24 times, how can it have the famous "film look" I keep reading about?

[I've read about pull-down many times--which I could understand it!]

As I read what I just wrote it sound like I'm ranting or something! Don't mean to be--I've read so much about how great it is to have 24p that I'm thinking I must be missing something.

Thanks!
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Old March 2nd, 2008, 09:23 AM   #8
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Is your shutter speed set correctly? Make sure it is set to 48 and not 60. This will help. Secondly, as mentioned before, when shooting 24p your movements a slow and smooth.

For action you can shoot at an even higher shutter speed, but the higher your shutter, the more light you will need.

About pulldown: http://en.wikipedia.org/wiki/Telecine#2:3_pulldown
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Old March 2nd, 2008, 09:50 AM   #9
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In my mind 24P is a FAD. There was a good reason to shoot this way in video when the intent was to transfer to film for a film festival etc. But the technique has to be film technique not the way video is shot. Shoot still closeups ( with the backround out of focus etc), no pans, very slow zooms etc. As mentioned in an earlier post 24 frames per second was chosen as the optimum cost for film stock costs for distribution and sound quality for optical sound tracks. You will notice that a lot of action shots in films are in slow motion, they are shot at high frames rates to stop the stuttering!!!!! There are some other technical issues in that a film projector will normally have 3 blades on the shutter and thus flicker the image 3 times for each frame ( 72 frames a second as far as our eyes are concerned, some even have 5 blades) So our eyes are satisfied from a flicker rate but the images are still only shot at 24fps which is really too low for any sort of rapid movement. The financial issues of smooth motion and high sound quality are irrelevant with modern technology but the film techniques are still valid for creating the emotional effect. We just do not need the slow frame rate in my opinion. I am appalled by the stuttering of background in a lot of TV programs these days obviously shot in 24p with little regard for the poor image they are producing.
Just keep in mind that most of the film techniques of shallow depth of field, dolly tracking shots, high contrast images etc are used to disguise the inadequacy of shooting at 24fps. You can still use these techniques for effect but really don't need to use 24P and risk all the stuttering.

Ron Evans
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Old March 2nd, 2008, 10:04 AM   #10
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D.J. & Ron THANKS! and yes, I'm yelling.

Very helpful and at my tech level! Really helps.
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Old March 2nd, 2008, 01:01 PM   #11
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Quote:
Originally Posted by Jaums Sutton View Post
D.J. & Ron THANKS! and yes, I'm yelling.

Very helpful and at my tech level! Really helps.
So Jaums, what WAS the shutter speed you were using before on 24p mode? Was it 1/60th sec? Like DJ said, try using 1/48th sec.

Also, i believe there are 2 different 24p modes on the Z7.
Kenny agrees with me... :
http://www.dvinfo.net/conf/showpost....3&postcount=57

Try both of them - theyre different. Refer to the manual. Let us know results. thanks.
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Old March 2nd, 2008, 01:10 PM   #12
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In my mind 24P is a FAD. There was a good reason to shoot this way in video when the intent was to transfer to film for a film festival etc.
Well I don't think it's a fad so much as it is just simply overused in situations where it shouldn't be. Use the right tool (in this case, frame rate) for the right job... 24P has its applications but it certainly ain't meant for everything. It's a great thing to have but it's been somewhat over-marketed.
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Old March 2nd, 2008, 05:27 PM   #13
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Just tried 24 & 24A [24A = Phase of the 60i conversion is reset each time recording starts].

As far as my eye is concerned, 24 is jerky when you do even a very slow pan on a crane or the actor moves, unless the shutter is so high [1200] that it looks like a bad horror movie on the dark side of the moon, which has been invaded by black worms.

From what I'm reading here and my experiments, seems to me 24 may be useful if you are transferring to film, otherwise, don't use it.
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Old March 3rd, 2008, 08:27 AM   #14
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Not quite so

*****FYI, film flashes twice a frame. It means there are 48 flashes per second.
It looks smooth compared to the digital 24p.[/QUOTE]****

Film operates at 24 frames per second, as far as frames goes. The film camera shutter rotates 48 times per second, that is true, but only 24 frames are being recorded as other 24 rotations are there for the film to be transport to the position for the next frame to be exposed. Film in film cameras does not flows through the camera continuously but intermittently: it has to stop for a short period for the frame to be recorded onto the tape. And due to persistence of our eyes that can not detect frequencies faster then 24 cycles it has been decided for purely economical (saving the tape) reasons to select the slowest non-detectable frequency for the rate of the film frames.

Nevertheless, 24p should not be jerky at any rate, jerkiness indicates that there is a problem in encoding - decoding system of the camcorder, I would say without actually seeing the footage and the camcorder/NLE sysyem setup.
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Old March 3rd, 2008, 09:14 AM   #15
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Our eyes definitely see 24 fps as 24 individual images. To fool us into thinking it is moving image they need to be flashed at leased twice as fast ( 48 times a second or two times for each frame). This is marginal for a lot of people and as such a lot of projectors have 3 or 5 blades on the shutter to flash the images 3 or 5 times each, raising the flash rate to a rate that our eyes perceive as motion( my own projectors have 3 blades so even at silent Super8 rate of 18fps they flash at 54 flashes per second). For instance the TV in UK refreshes at 50hz and in North America at 60hz, that means images are flashed at the viewer that many times. When I lived in the UK I didn't see the flickering but since living in Canada for a long time every time I go back to visit it takes me almost a week before the flicker in the TV's is less noticable. So 50 frames a second in my mind is very marginal. Most films one sees from a projector are likely 72 flashes a second or more. The image thus doesn't flicker but any movement on the screen is still only at 24fps which is inadequate for any fast movement especially across the screen sometimes call judder to distinguish from the flicker rate. There are lots of books on film technique to mask this effect and these techniques are what create the film look not really 24fps judder which in my mind is a defect to cover up!!!! The other issue with shooting 24p video is playback. One needs a screen with a refresh rate a multiple of 24 so that there isn't a conflict in playback rate. Unless one has a 120hz LCD for instance there will be conflict that needs to be adjusted with pulldown of some form that could make the image motion worse!!!! OF course this doesn't apply if the purpose was to shoot on video( cheaper than film) and transfer to film for projection. Other than that 25P for Europe/PAl countries and 30P for North America would be a much better choice for video for progressive capture if one really needs to have such a slow frame rate. Personally I would like to move to 60P to have really smooth motion.

Ron Evans
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