Horizontal strekking lines while panning

[TingSern Wong]

Hi all,

I was out on New Year's eve doing video coverage for an adventure race using XL2. Camera set to 25p (PAL) and 16:9. Lens stabilisation was OFF - camera mounted on tripod.

I noticed that when I pan the camera (slowly - or so what I thought was slow enough), the footage showed noticable streks on subjects moving horizontally across the scene that lasts for 1 second. It disappeared subsequently ....

Lighting was pretty low - day was overcast and raining outdoors.

Any idea what could be the cause and how to fix the problem? I don't think the camera is at fault - more likely an artifract of the 25p thing.

Thanks,
TS

[Chris Hurd]

It is a frame rate issue. 25p is not well suited for what you are doing. For racing or any other activity involving fast moving objects, you really should consider shooting in 50i.

[TingSern Wong]

Thanks for the info. Now I know the limitations of 25p. Too late - as usual. Learn and never forget.

TS

[Stefan Scherperel]

Chris I respect you fully for your opinions, but I have to disagree with your last post. 24 and 25P, I believe can be used in any situation as well as it is shot correctly. One of the best examples of this is NFL films. Football (American) is a fast moving sport, and I believe that nothing shows the game better than NFL films coverage. This is not the stuff they show on ESPN, this is 16mm footage, shot from every angle concievable, with every meathod concievable, shoulder mounted, hand held, tripod mounted, you name it.

The smear that you were most likely seeing would be due to your shutter speed. For fast movement it is better to use a higher shutter speed. Now this will give a different look, more like the look of fast action in movies. but if that is the look you are going for, then that is what you get. If you want more of the ESPN news look then shoot 50 or 60i. It is an asthetic decision, but after working with 24p footage for so long it is extremely hard for me to go back to interlaced footage.

[TingSern Wong]

Hi Stefan,

Thanks for the info. But, what can I do if the lighting level is already very low - aperature already almost to the limits (f/2.8 and wider), asking me to increase shutter speed? I can't use video light for this application, because the distance will be pretty limited.

Question -
Can I use 25p (or 24p in NTSC) if the shutter speed is faster than 1/25 second? My 2 cents say - if I want to shoot at 25 frames per second, the shutter has to be exactly 1/25 second. Am I right? If No, please enlighten me then - puzzled now ... if I can force the shutter to a faster speed (assuming that light is bright enough for me) - and still can shoot 25p mode, how does the camera handle that?

Thanks,
TS

[Stefan Scherperel]

TingSern Wong;
You have some good questions. First, let me just say, that when shooting in 24-25p, it is best not to use a shutter speed of 1/25th. That is a very slow shutter speed and you will get a lot of motion blur. The default (atleast on the DVX) is 1/48th second shutterspeed. You can change the shutter speed to anything the camera will permit, not sure what that is on the XL2, but on the DVX it is 1/1000th even in Progressive. NOw, if your light is low, shooting in progressive will give you a slightly darker image, so there are two things you could do. Shoot interlaced, or use gain. But if you are shooting anything that moves, 1/25th second shutter speed is going to give you blurry results.

[David Lach]

TingSern, for what it's worth, I've used the gain up to +6db with the XL2 in certain situations, a thing I would never have considered before, but the XL2 remains very clean (well clean enough) up to +6db.

After that, you decide whether or not it is best to shoot interlaced or progressive. Your shutter speed should not go lower than 1/50 for moving subjects and if lighting permits it, go for 1/100 if you want crisp images without motion blur for very fast action (running, moving cars, etc). That will give you the "Saving Private Ryan" kind of motion. Only an aesthetic decision.

[Sven Ohrvik]

But how come the default shutter speed for 25p (PAL) is 1/25 and not 1/50?

Sven O.

[Richard Hunter]

TingSern, you should try it on 1/50s. You will still get some motion blur on fast moving subjects, but at 1/25 EVERYTHING will have some camera shake as well as the motion blur. I'm also using PAL and did not get such bad results as you mentioned when shooting 25p.

Richard Hunter

[Marty Hudzik]

For what it is worth I see almost no perceivable advantage to 60i or 50i on the XL2 when it comes to f stops. On the DVX there was a noticable difference between the progressive mode and the interlaced mode. I was forced to use interlaced at certain low light shoots. But with the XL2 I Cannot perceive any increase here. Therefore I can shoot progressive either way.

I have not scientifically proven this but I think this is the case. Anyone else seeing this?

[TingSern Wong]

Thanks for the great help. Now, I will go and do some experiments and see what the camera can tolerate then. I didn't know that 25p allows for the shutter setting to be set higher than 1/25 second. Will try it out and let you guys know the results then.

[TingSern Wong]

I am very sorry. I have raised an almost non-existent issue .... after doing very careful controlled testing using my XL2 and my PC, I finally nailed the culprit.

I set my XL2 to shutter speed of 1/25 and again at 1/210, both taken using 25p mode. Aperature set accordingly to expose image perfectly. Metering was using Manual mode.

Shoot two identical scenes, one at 1/25 and the second at 1/210. Both of them were panned from left to right and back again. Unloaded the tape using my Sony DSR25 - via firewire into my Canopus DVStorm card. Read into hard-disks. Viewed the scenes critically, and compared it with viewing it via DSR25 output to Sharp Aquos LCD TV.

Problem? The motherboard I am using can't tolerate an overlay viewing quality of HIGH. The PCI bus gets overwhemed by the Canopus video card. I can't see any strekking on DSR25 output on LCD TV - means tape is recorded perfectly. But the horizontal strekking are visible on the PC's monitor. If I set the overlay viewing quality down to medium (as opposed to high), the strekking on the PC monitor's display goes away.

***
Also, I can conclude that there is NO visible difference on the XL2 when recording in 25p mode at shutter speed set to either 1/25 or 1/210 (or whatever faster shutter speed other than the default of 1/25 second).

TS

[Kevin Kocak]

You should always use an external monitor to view your work. You just can't trust a computer monitor unless your output is to be viewed on the computer.