Strobing / aliasing

J

James M

Member
I used the AF101 in the studio for the first time today and experienced a nasty artefact I hoped had been left behind with DSLRs.

Check out this clip for a rushed example - fast panning objects (highly contrasting) seem to judder / strobe / alias. Whatever you want to call it. The vacuum handle shows it well, as does the edge of the black flat. I first noticed it on a static shot that had a model passing through frame.

Is there a way around this? I was shooting 1080 25P - shutter speed at 180d/50th, with detail & v detail at -2, master ped at +1, cine-like gamma v, and norm 2 matrix. I'll be happy to discover there is something I was failing to do here... as long as that isn't shooting on 35mm film.

Thanks,

James

PS Video uploading at time of posting / while I go to bed.


----Edit----

Here's the working link, but doesn't look quite the same/as bad encoded in h264.
http://vimeo.com/19720008
 
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Well -- it sounds like you were doing a fast pan across an object, and you don't like the judder that comes from that? That's an inherent, unavoidable characteristic of shooting at a slow frame rate (24p, 25p, etc).

If you want it to be smooth, you've got to either a) slow down your pan, or b) speed up your frame rate. If you shot that at 50fps, there would be no juddering.

But this isn't an AF100 issue, this is inherent in the film frame rate. You would encounter this same juddering with 35mm film, 16mm film, a DVX100, a 5D, an HMC40, an EX1... anything that you were shooting at 25p would do this.
 
I don't know if anyone can see the above clip, because I can't even get Vimeo to load this morning. I know it's a very fast pan above but when i first noticed the effect, it was just someone passing through frame.

I don't think this is just a slow frame rate thing. I've shot 25P on dsr/ex and my formal training was on 16mm. I've never noticed what I saw yesterday, except on 5D. Previously I've had nice, blurred motion artefacts with a little chop - not this drastic juddering. However, I have never shot on a plain white coving background before (except with 5D), so may be that is bringing out the worst in this.
 
Id call that Vertical Sync or vsync, It does look bad, Ive never noticed it before with my HVX, will have to keep an eye out. I havent really had a chance to try out my AF102 yet.

have you had any improvements with different settings?
 
While I haven't done a proper tweak/frob investigation to see if anything helps, I have tried nudging some of the obvious candidates about a bit. So far, absolutely no change to that effect.

Today I was doing a vertical jib, and the effect became really pronounced. I'll find out from my client if it's okay to post a clip, because it severe. Again, I think it might have something to do with high contrast.
 
I've now seen the same effect in stuff shot with other cameras including my HVX, just never noticed it before. Although it didn't look as bad as the example in this thread.

Can some one who has used film cameras tell me if they do the same thing?
 
Yes they all do the same thing. Watch "Network" when what's-her-name is running down the hallway, it's a perfect example -- dark doorframes against white, and strobing so hard you'd think your eyes will break.
 
Oh wow, I just got shown the end of "the good the bad and the ugly" there is huge amounts of it. Never noticed it previously.
 
It's always there. It's always been there. But typically the cinematographer will structure a shot in such a way that your eye will be distracted by something else, and therefore not focus on the strobing. In the previous example I gave of "Network", the shot is a tracking shot of someone running down a hallway. If you look at the subject, you won't be focusing on the doorways as they strobe LIKE HELL. But if you actually look at the doorways, you'll see massive strobing.

Normally you don't see it in film not because film behaves any differently; instead you don't see it in film because they don't typically execute shots in such a way that would show it.

But it's an inescapable artifact of shooting at a slow frame rate.
 
The strobing is one the things that drove me crazy on the 7D. I was hoping the AF100 would be better, but apparently not then, if I shoot at 24P? With the 7D it was not just strobing, but it did a kind of stair-stepping thing with verticals or near verticals as I panned. I assumed it was a result of line-skipping because of the stair-stepping.

So what should I do to avoid it then? Shoot at 30P? 60P? If you put those clips back into a 24P timeline will they start strobing again, or will they be re-interpolated in such a way that they would stay smooth?
 
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