"Rolling strobing" or something.

H

Hissigman

New member
So, I'm thinking of buying a 550D, and I'm well aware of the rolling shutter/aliasing problems like skew and colour contamination, and how to avoid them. However, in the last few hours I've seen quite a few clips with this rolling strobing kind of error (see examples), as if the clips were filmed off a screen with a different refresh rate than the shutter on the camera. Any ideas as to what could be causing this and how it can be avoided?

Example 1 @ 2:24

Example 2 @ 0:15
 
Shutter speed, shutter speed, shutter speed, people HAVE GOT TO STOP MESSING WITH THE SHUTTER SPEED.

Use 1/60th in the USA, or 1/50th in PAL territories. NEVER EVER EVER use 1/250th, 1/500th, or anything like that.

here's another thread, there are probably a dozen threads that talk about this.
http://www.dvxuser.com/V6/showthread.php?p=1947823#post1947823

Spread the word on every forum, everywhere. No 1/48th. No 1/250th. If it's a CMOS camera (including EX3, Red One, 7D, 5D, 1D Mark IV, HV20, it doesn't matter, as long as it's CMOS) then it's going to have this problem, and the only way to solve it for good is to use 1/60th (in the USA) or 1/50th (in Europe) and DON'T CHANGE IT.
 
what about shooting 1/30?

edit: the reason i ask this ^ is because I haven't noticed anything strange when shooting 24p with 1/30th shutter speed and since my 28mm lense biggest f stop is 3.5 it helps shooting indoors with iso less than 1600
 
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when you really need it 1/30 helps for lowlight and there is apparently not much of an issue with flicker/strobing here in europe at 50hz
 
Barry_Green said:
Shutter speed, shutter speed, shutter speed, people HAVE GOT TO STOP MESSING WITH THE SHUTTER SPEED.

Use 1/60th in the USA, or 1/50th in PAL territories. NEVER EVER EVER use 1/250th, 1/500th, or anything like that.
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I think its better to teach why the "rule" is there and then explain that you can break it if you know what you are doing, dealing in absolutes is NEVER (:2vrolijk_08:) a good thing.

Take that first example, that would be great footage if you were to composit onto a tv in a shot, and save time in post creating a "realistic" (ie shitty) tube tv look.
 
So to repeat diego's question...there's absolutely no way to get the high shutter, "saving private ryan" look,( which I happen to luv to do for select shots on my dvx) with a cmos camera?
 
So you can't go for the "fast pace" strobing effects you see in 28 Days Later with a DSLR?
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Someone correct me if I'm wrong but I believe this shutter speed issue only occurs when filming with lamps connected to a power source. So the "fast pace" strobing could be achieved outdoors/with natural light or with flicker-free fluorescents. Also I believe using incandescent/tungsten light is "safer" than regular fluorescents since the filament doesn't have enough time to cool down between cycles.
 
I use shutter speeds upwards of 1/50th all the time. When shooting surfing at 50p I will go up to 1/1000th on occasions. Otherwise you end up with blurry crap with no detail.

I agree that dealing in absolutes is not a good idea. Yes, the 180 degree shutter rule is the standard because of the right balance between stobiness/motion blur blah blah blah but there are times when the situation calls for a different shutter speed.

I do however, agree that people need to make themselves more aware of how their camera will behave with different settings and how to work around different problems. And in this scenario, it seems like sticking to 1/50th (or 1/60th) is the easy solution.
 
kevinottawa said:
I think its better to teach why the "rule" is there and then explain that you can break it if you know what you are doing, dealing in absolutes is NEVER (:2vrolijk_08:) a good thing.
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I've been explaining this rule for about three or four years now. Go back to my "rolling shutter" article in the articles section. Ever since the first CMOS cameras hit the market, I've been trying to tell people about this particular artifact.
 
Hissigman said:
Someone correct me if I'm wrong but I believe this shutter speed issue only occurs when filming with lamps connected to a power source. So the "fast pace" strobing could be achieved outdoors/with natural light or with flicker-free fluorescents. Also I believe using incandescent/tungsten light is "safer" than regular fluorescents since the filament doesn't have enough time to cool down between cycles.
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This is correct. The issue happens with rolling-shutter CMOS camcorders using a ballasted light source (fluorescent, HMI, mercury vapor, or sodium vapor, at least). It won't happen under daylight, or under tungsten.

The reason I went with the "never never" angle is because there are many, many, many people coming to the DSLR (or to video in general) who seem to think it's okay to just change the shutter speed to whatever, even to control exposure. And that flies in the face of conventional cinematography techniques. We don't use the shutter to control exposure. The shutter speed is fixed, unless you have a very special need. 99.9999999% of the time this issue comes up, it's because someone changed the shutter speed in a scenario where they didn't have to.

So what I'm trying to get across is: motion video is motion video, and the same rules that have been in place for 100+ years still apply. Leave the shutter speed alone. It's a basic, fundamental rule (like "focus on your subject") that people should learn and ingrain. If, someday, they want to experiment with different shutter speeds for a specific effect, well, great -- go ahead -- but learn the basics first. Changing the shutter speed on a CMOS camera can and will lead to the artifacts displayed in this thread, and if you just leave the shutter speed on a video/film-friendly default value like you're supposed to, you can forever avoid that artifact too.
 
deltoidjohn said:
I use shutter speeds upwards of 1/50th all the time. When shooting surfing at 50p I will go up to 1/1000th on occasions.
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And outdoors you can do that without worry. But outdoors is one of the few places you can. Problem is, we see people all the time trying to shoot at 1/250th, everywhere -- and you just can't do that without causing this artifact frequently.

but there are times when the situation calls for a different shutter speed.
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Yes, there are times. Rare, infrequent times, when looking for a specific type of look. And if people would understand that changing the shutter speed should be a rare, infrequent task that is done only and solely to pursue that different look, then we'd see far fewer complaints and ruined footage!

So, if you'd like the statement revised, maybe it should be "never, never, never, never, never, never, never ever change the shutter away from 1/60th (NTSC) or 1/50th (PAL) unless you know EXACTLY what you're doing, and you understand that changing to a faster shutter speed will cause rolling scrolling bars in your footage in many circumstances, and you accept that risk, and you understand that you might end up with unusable footage, and the only way to avoid that is to just stick with the 1/60th (or, for PAL users, 1/50th) shutter speed."
 
Barry, if I know I am in no danger of a rolling bar pattern I should be able to shoot 1/50 NTSC without any worry of this type of artifacting as it is a slower shutter speed (more motion blur) than 1/60, correct?

I mainly use 1/60 in front of streetlights, etc, and 1/50 for almost everything else. To check for the pattern I will usually record say, a 1 min clip, on a white wall under the light if possible, while still setting everything up, and then play it back in fast forward and see if there is a rolling bar problem.
 
Ben_B said:
Barry, if I know I am in no danger of a rolling bar pattern I should be able to shoot 1/50 NTSC without any worry of this type of artifacting as it is a slower shutter speed (more motion blur) than 1/60, correct?
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Yes -- but the question then becomes, for many -- what's the point? You get a very, very slightly different look, at the risk of forgetting and therefore screwing up footage later on... as long as someone is very diligent, they can always avoid the issue. For those who don't diligently check their shutter speeds and lighting, it's infinitely easier to set it on 1/60th and forget about it.

I mainly use 1/60 in front of streetlights, etc, and 1/50 for almost everything else. To check for the pattern I will usually record say, a 1 min clip, on a white wall under the light if possible, while still setting everything up, and then play it back in fast forward and see if there is a rolling bar problem.
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That will work; a perhaps easier way is to just crank the shutter up to 1/1000. If the rolling bars are going to be present, you'll see them live on the viewfinder.
 
ok so i have a question...is this not visable on the LCD or monitors while these people are shooting? I mean if u see it then i'd think u'd try and do sumn about it. But if somehow it doesnt show up till you go to edit then i'd understand.
 
jambredz said:
ok so i have a question...is this not visable on the LCD or monitors while these people are shooting? I mean if u see it then i'd think u'd try and do sumn about it. But if somehow it doesnt show up till you go to edit then i'd understand.
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Some of the LCDs and monitors might ghost a little bit and people might blame it on that?
 
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