canon and sony hd cams blurr

auggybendoggy wrote on 7/21/2007, 10:29 AM
Guys,
I read people complain about the sonys having a blurr problem with panning the camera. I believe it involves the fx1 and the z1u.

I might understand a bit. I shot in a grove of trees spinning med speed right up through the trees. so in the middle of all these trees I pointed the camrea straight up and you see the tree tops spinning.

when I took it into vegas and slow motioned it it's very blurry and seems sort of like ghosting...

I realize that all moving objects or subject will blurr (nature of things) but does canon handle this better? Perhaps I should just get the canon hd cam instead of the z1u. I was avoiding it since our first cam is a fx1 and so I wanted there to be no color difference between the 2 cams, so I thought using a z1u and a fx1 would work better than a xh1 and a fx1.

My guess is all cameras will do this unless they shoot 60fps or some higher rater.

Aug

Comments

farss wrote on 7/21/2007, 12:22 PM
It's called motion blur, that's why still photographers don't wave their cameras around when shooting at 1/60th of a second. Faster shutter speeds reduce the effect however for moving images the result will start to look rather stroby. One can increase the fps but how are you going to show the footage?

That's before you consider the question of the HDV encoder trying to cope.

Bob.
riredale wrote on 7/21/2007, 12:26 PM
Well, I've never noticed any sort of artifact with my FX1. As for motion blur, do a second test where you intentionally use a faster shutter speed such as 1/500. I would doubt there is any FX1 artifact. Come to think of it, I'll try it out in a little while...
JJKizak wrote on 7/21/2007, 1:48 PM
As long as the Z1 is in full auto it won't blur. Anyway that's the way it is in mine.
JJK
ushere wrote on 7/21/2007, 4:34 PM
have shot fast moving rodeo footage with my v1 at 50, no sings of any visual artifacting...

leslie
riredale wrote on 7/21/2007, 4:34 PM
The "blur" you see is interlace, which is a part of the 1080i standard, and not having anything to do with the camera. The camera is recording two separate scans to the same frame, with one scan following 1/60th of a second (in NTSC countries) after the other. I shot a few seconds of rapid motion at 1/60th, and then a few seconds at 1/4000. In both cases there appeared to be a double image, because there was. In the 1/4000 clip, objects were very clear and sharp.

Shooting progressive would eliminate this issue, but then this is an issue only under certain viewing conditions, and shooting progressive at 24Hz (which is typical) introduces a whole new set of artifacts.

It is certainly true that the HDV compression process (MPEG2) taking place real-time inside the camera is taxed very heavily in situations where every frame shares very little with other frames, which is what would be the case in a very rapid pan or rotation. But even then the artifacts are hardly noticeable (because of the rapid motion) and in any event every HDV camera is going to suffer the same artifact, more or less.
farss wrote on 7/22/2007, 12:37 AM
when I took it into vegas and slow motioned it it's very blurry and seems sort of like ghosting...

Ah shite, I missed that bit, my bad!
If you slow down footage, regardless of what it's shot on, even film then you are also effectively slowing down the shutter.
For example if you slomo to 50% material shot at 60i with 1/60th sec shutter then it'll appear as though you'd used a shutter speed of 1/30th sec. Solution is to increase shutter speed by the same amount you intend to slomo. In the previous example you would increase the shutter speed to 1/120th sec.
This is why a lot of sports footage appears stoby at normal speed, they're using a faster shutter speed so they can get good slomo.
The same applies if you plan on doing stabilzation in post, use a faster shutter speed.
All this is regardless of type, model, make of camera and compression system used.

Bob.
MH_Stevens wrote on 7/22/2007, 7:55 AM
I have not experimented with my FX1 with shutter speeds other than 1/60th. Maybe this is a good opportunity to ask farss for a brief primer in this subject. When are shutter speeds OTHER than 1/60th appropriate.
farss wrote on 7/23/2007, 3:54 AM
This applies to any camera shooting moving images, film or video.
My apologies for anything I get wrong also!

Traditionally shutter speeds are 1/2 of the time between frames. On a movie camera shutter speed is measured in angle and the traditional shutter opening is 180deg = 1/48th at 24fps. I only mention this because it may make the concept a liitle easier to understand, well it did for me.

So why use a different shutter angle / shutter speed?

1) Creative reasons. A faster shutter makes motion more jerky due to the reduction in motion blur. I'm told this creates a certain 'feel' to the action of urgency or stress. Film cameras don't seem capable of very fast shutter speeds so stobe lights seem to be used to get really fast shutter speeds if needed.

2) Slow motion. Lets say we find the look of a 180 deg shutter ideal. The faster the camera runs the shorter the time the shutter is open and when the film is slowed down the motion blur remains the same, i.e. 1/2 of the time between frames. Now most video cameras cannot be overcranked, we're pretty much stuck with one frame rate, say 30fps. So we do slomo in post. At 33% our apparent fps is 90fps but our shutter was 1/60th. Now we have a problem! 1/60th of a second at 90 fps = a shutter angle of 540 deg. In other words the shutter is open longer than the time between frames, major blur will be imparted to the motion.
We therefore need to compensate for what we're going to do in post when we shoot the footage. If we're going to slomo to 33% we need to decrease the time the shutter is open by the same amount. So 1/3 of 1/60 = 1/180. The next fastest common shutter speed is 1/250th.

3) Motion Stabilization in post. Imagine if you panned the camera up quickly, just the same as happens when you shake the camera. A stantionary object in the shot will have a trail of motion blur, as long as the shutter is open for.
Now if by some digital magic we correct for the motion of that object in the frame we still have the motion blur. Ooops, the object isn't moving but it has motion blur. If the camera was bouncing up and down the motion blur trail goes up and down on the stationary object and that looks pretty wierd.
Solution again is to increase the shutter speed, no simple rule here. If you're shooting a long shot out the back of a truck on a bad road you'd probably want the shutter as fast as the available light will let you go. If in doubt err on the side of too fast.

4) If you want to extract stills from the video. Motion blur is going to kill your stills, faster shutter speeds especially if hand held. 1/125 seems to be the norm for stills unless long shots.

5) This IS HDV specific. There's some claims that faster shutter speeds help the encoder when there's lots of motion. I doubt this fixes everything but it would seem to help. I'd be carefull though if you don't have a lot of light. Faster shutter speeds could mean gain and that could increase noise which is also a problem for the encoder.

Bob.