PDA

View Full Version : 7D Unknown Artifacts



nickylund
02-17-2010, 11:19 AM
Not quite sure what is causing this:

http://farm5.static.flickr.com/4024/4365289135_a75aa4e91a_b.jpg

It's a still taken from a 1920x1080 23.97 video.
Shot at 3200ISO
50 shutter
2.8 apeture
36 frame pan

The light pole and other vertical lines have a duplicate image during the pan.

I thought it might be the firmware and the ghosting issue I read about since I hadn't updated to the latest version. It doesn't look like regular rolling shutter issues.

I haven't had a chance to go back out and run some more tests.

Any ideas?

Thanks!

Strobe Media
02-17-2010, 11:48 AM
it's obviously a UFO

Martti Ekstrand
02-17-2010, 12:00 PM
1/50 is long enough shutter speed to let street lights (and fluorescents) go through 2-3 cycles during exposure if you are in a country with 60 Hz AC. Use 1/60 instead in situations like this.

Barry_Green
02-17-2010, 12:15 PM
Never ever ever ever ever ever ever ever ever ever ever ever ever use 1/50 on an NTSC 7D or 5D or GH1.

Just don't.

Please.

Ian-T
02-17-2010, 12:30 PM
All of a sudden I feel stupid. But I have been using 1/50 shutter for video because i was told that's close enough to 1/48 (which it does not have). So, should it be 1/40 all the way?

nickylund
02-17-2010, 01:52 PM
Thanks everybody.

Barry_Green
02-17-2010, 01:53 PM
1/60 if you want to avoid problems.

1/50 if you like problems.

1/40 if you like more blur, and should also avoid problems.

PaPa
02-17-2010, 01:59 PM
Just to add to Barry's information. Yeah, if you're shooting under fluorescents or light fixtures that don't have a proper flicker, just bump up to 1/250th and see if you see strange artifacts. If everything is good, then like me, you pretty much want to emulate 1/48th so you can take the risk and shoot at 1/50th.

I can see a subtle difference between 1/60th and 1/50th, and after these discussions i will seriously check more accurately by upping the shutter to see if artifacts are present, but if you're good then i see no reason why not to shoot at 1/50th.

Not to be a pain Barry :)

soarprod
02-17-2010, 02:01 PM
1/60 if you want to avoid problems.

1/50 if you like problems.

1/40 if you like more blur, and should also avoid problems.

Hey Barry,
Can you elaborate on those problems? I have been shooting for months with the 7D, 23.98 and 1/50 shutter - I have not experienced anything out of the ordinary.

dcloud
02-17-2010, 02:58 PM
I never had problems with 1/50. but this gives me the idea to switch to 1/60 if i encounter these problems

shaocaholica
02-17-2010, 03:01 PM
Hey Barry,
Can you elaborate on those problems? I have been shooting for months with the 7D, 23.98 and 1/50 shutter - I have not experienced anything out of the ordinary.

How often have you been shooting at night or indoors?

Barry_Green
02-17-2010, 04:22 PM
I can see a subtle difference between 1/60th and 1/50th, and after these discussions i will seriously check more accurately by upping the shutter to see if artifacts are present, but if you're good then i see no reason why not to shoot at 1/50th.
Like with any rule -- if you know WHY the rule was instituted, and you know what circumstances caused it to be instituted, and you're certain that your intended use falls outside those circumstances, then sure, go ahead.

Just remember that you only have yourself to blame if you forget!

But what needs to happen is we need to exterminate this idea that "1/50th is the right shutter speed because it's more filmlike" idea that folks have. 1/50th can cause damage to people's footage. Every NTSC shooter should just default to 1/60th unless they know for absolutely sure that 1/50th is "safe" in their particular shooting circumstances, and that they actually care about the tiny differential in image look between 1/60th and 1/50th.

Martti Ekstrand
02-18-2010, 03:17 AM
Every NTSC shooter should just default to 1/60th unless they know for absolutely sure that 1/50th is "safe" in their particular shooting circumstances, and that they actually care about the tiny differential in image look between 1/60th and 1/50th.
There, I fixed it for you.

Shooting 1/60 in a land with 50 Hz AC cycles can be just as destructive to the footage as shooting 1/50 in a land with 60 Hz AC cycles.

Considering how often this issue pops up it might be a good idea with a sticky of this subject in at least the general DSLR section, if not in all the camera subsections.

rhervag
02-18-2010, 03:53 PM
yes for us from PAL land, there really is not much viable option besides 1/50 at all. even 1/100 is problemeatic on fast ballast type of lights.
there is this bar with tri-colored 12V leds that would strobe at every shutterspeed available on the 5D because it is 30p while it is perfectly fine with the 7D at 25p.

some tests from 50Hz ligths

http://vimeo.com/4972364

http://vimeo.com/4991966

Barry_Green
02-18-2010, 04:26 PM
Excellent videos, thanks for posting those.

Folks, you have been warned. If you're in NTSC territory, put the shutter on 1/60th. If you're in PAL territory, put it on 1/50th. Anything else can lead to trouble.

Michael Olsen
02-18-2010, 04:51 PM
Excellent videos, thanks for posting those.

Folks, you have been warned. If you're in NTSC territory, put the shutter on 1/60th. If you're in PAL territory, put it on 1/50th. Anything else can lead to trouble.

I vote for a fully fledged PSA talking walk-on-the screen flash announcement for the forums, Barry.

nickylund
02-24-2010, 03:40 PM
http://farm5.static.flickr.com/4023/4386180780_0c49c83f95_b.jpg

I tried the same street, different lens, but with the 1/60th shutter. However, the doubling artifacts are still showing up. Most notably int he light poles.

Could there be another setting that I have turned on or off that might cause this?

Thanks again for any insight.

Barry_Green
02-24-2010, 03:49 PM
How are you extracting these stills? Are you putting 60p footage onto a 24p timeline or anything like that?

nickylund
02-24-2010, 03:56 PM
The camera file is transcoded to Pro Res and then I'm pulling the still from Nuke.

But I can see the artifact in the H264 .mov file that came straight off the camera and in the viewfinder during playback.

I'm using the EOS Utility to bring the footage off the camera if that helps.

Kellar42
02-24-2010, 04:48 PM
This is good to know...