HVX "Judder" issues

M

maneymedia

New member
I recently shot a short using the HVX (part of the 48 Hour Film Project). I was very impressed with the camera overall. However, when viewed on a set (both HD and SD) the film had a slight strobing/flicker effect to it. I was told by a reliable source that this is called 'judder' and has to do with the fact that it is shot in 24p and in HD (I'm also assuming it has something to do with 2:3 pulldown..maybe not). I shot the short in 720p native. To many, the flicker is virtually undetectable, but I notice it.
Any suggestions out there to reduce this? Is there something I can do in post?
- Maney
 
If the shutter speed is 1/48 of a second or longer; 1/24 of a second is better than 1/48, the strobe like effect will be reduced. High shutter speeds, speeds shorter than 1/48 of a second will make the strobe effect stand out.


Bob Diaz
 
If you read Barry Greens DVX book (HVX version yet) and many other info sources there is a strobing when shooting in 24p/pa /fps, there are guidelines to pan times etc and methods of reduction i.e. focusing on a subject during pans etc. Watch any DVD of any movie and you WILL see some strobing during pan and tilts, depending on what the dp or director thought acceptable will determine how much but I havent watched anything lately I havent been able to notice it on if looking for it.
 
Hi guys i'm cuurentlyalso working wif hdx-400 and i also see judders in quick pans or very slow pan shot can u guys advise me about this judder ? can it be gone by post ? and i work wif films b4 but that was years ago and only as an assistant
 
That's normal for 24fps shooting. It is there on film shooting with 180 degrees shutter (that's 1/48 exposure). In fast pans the motion is not fluid and starts appearing as a series of still frames. This has to do with the percentage of the image changed from frame to frame and this boils down to the vector of movement related to the time required for the movement. This is pan velocity. At a specific velocity the motion perception breaks. Try a much faster shutter and it will break easier and with slower pans. A slower shutter would give you some blur that will make it more fluid.
 
Pulldown to NTSC frame rates does not help of course. It makes the velocity of a steady pan change from frame to frame and the anomally comes in cycles which is easier to perceive (6 times each second).
 
hi pat tanks 4 the reply................but the problem is the camera is loaned to us by panasonic and we were told wif stict orders not to adjust any settings at all :( but every1 is asking whether can it be done by post coz it restrict loadsa camerawork 4 us
 
This is a very intertesting topic. When someone says judder I would assume that it is from shooting above 1/24.

However my experience with the DVX is that the 1/24 shutter kinda looks like crap in that it really smears. I know it is technically the same rate with film, but you don't seem to notice it as much. When people talk about more fluid at 1/24 all I see is ugly smear. Anyone else agree?

I actually like to shoot above 1/24. It seems to become a bit more crisp. I know if you go too high you get that really crisp stutter. But actually a lot of feature films shot on film are using faster shutter speeds. When shooting music vids you can really get away with it more.

I wonder how the HVX will look at 1/24? Maybe the higher resolution will reduce the smear at 1/24.

Just my opinon.

Cheers,
Chris
 
Actually 1/24th is not the shutter angle normally used in film. That is a very slow shutter speed, basically blurring everything that you shoot. I would highly reccomend not using that shutter speed to reduce "judder" but learn how to shoot a camera at 24p while using the standard "off" shutter on the DVX. Off does not mean that there is no shutter, I believe it is set to 1/48 or 1/50, but that is as close to a 180 degree shutter (commonly used on most films) as you can get.
Out of blurred is blurred, doesn't matter what resolution you shoot at, it will be blurry, so the same thing goes for the HVX. The only time I would ever use 1/24 or have used it is during a wedding reception, when the light is very low. I prefere to use 1/24 over gain, but that's a whole other story.
 
Film cameras typically have a shutter that is like a section of a circle. Like a piece from a pie. That rotates and lets the film get light and also the operator to monitor what goes on film, alternating between the two. The normal shutter angle (the part of 360 degree circle that goes to the viewfinder) is 180 degrees at that is 1/48 for 24fps. 1/24 is almost impossible, the film would be constantly on exposure. It does not leave time for having light reach the viewfinder and time for advancing the film. So the operator has a black viewfinder and the film is getting light while the film is moving which is not what we are after.
 
Agreed 1/48th should be used, 1/24th should only be used for effect or for extreme low light, it will cause abnormal smear.

If 24P is too juttery for you, shoot in 30P. It can be problematic for film or PAL transfers but really does look great.


ash =o)
 
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