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Help An Editor Identify This Problem?

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Sean ONeil
Help An Editor Identify This Problem?
on Sep 8, 2008 at 2:13:36 am

I'm an editor working with a client who produced an unusual video project.

It's a special video projection system that uses a fisheye lens on a convex dome type screen. Meant for trade shows.

They shot some footage for it using a Panasonic Varicam with a fisheye lens plus and an adapter to make the lens work on the Varaicam.

When I first looked at it I saw this textured layer covering the whole image. It's actually really bad. Below is a still of it and you can clearly see the problem in the sky


You may want to download the image to see it full size.

The worst part is that the layer is not static. It continuously rotates in a circle.

The vidoeographer did not catch the problem I guess because it rotates so fast it shows up as a a mild flicker on his monitor. But the overall result is devastating. The detail is non-existent - it looks like it was shot on a cellphone camera.

We think the lens adapter may have been defective but don't really know.
Can anyone who understands optics and cameras explain how this could have happened? Thanks!


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Ben Ferrer
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 5:02:16 am

Hi Sean,

I'm guessing that is the texture of the ground glass inside the lens adapter. That is, if a 35mm lens adapter was used to get a 35mm fisheye lens mounted onto the camera. I don't have much experience with that kind of setup, but I would suppose that the adapter was either of lesser quality or the motion of the ground glass was on the wrong setting for use with that lens.
Also, the camera may have had the detail setting on, which might cause the camera to add detail to edges including the visible texture of the ground glass.

Perhaps you could layer the footage on your NLE timeline and add a gaussian blur to the bottom layer. Then try keying out the blue sky as much as possible to reveal the softened image underneath.

I could be completely wrong, but that would be my first guess.

-Ben


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Sean ONeil
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 5:10:28 am

Thanks Ben.

Sean


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Rick Amundson
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 1:29:59 pm

The grain is definitely the ground glass from the lens adapter. There are a few factors that can add to this problem. I only work with the Pro35 so I can only speak to my experience with that system. There is an adjustment dial on the Pro35 that allows you to change the speed of the rotating ground glass. This helps to hide the grain in most of the image when dialed in correctly. It looks like ____ when it is not. It takes experience to analyze the whole image and determine the correct level of compensation before hitting record.

Also, on a clear, bright day (like in your image) if the camera is stopped then the increased depth of field with exaggerate the effect even more. Lens adapters crave a shallow depth of field. Tell the shooter to use ND filters to get the lens close to wide open.

Finally, if the detail in the camera was turned on at all, it will exaggerate the effect as well.

Unfortunately I don't have an answer for a fix in post. You know the old saying, "Garbage in ..." I think the multiple layer, blending mode, key out the sky idea is the right track though.

Best of luck!

Rick Amundson
Producer/Director/DP
Screenscape Studios
Bravo Romeo Entertainment
http://www.screenscapestudios.com
http://www.bravoromeo.com
http://www.indeliblemovie.com


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Todd Terry
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 2:57:55 pm

Yep, that is absolutely positively the groundglass on the lens apapter.

I'm with Rick, a fellow P+S Technik user... either the speed of the groundglass was not dialed in just right, the partciular converter used does not have adjustible speed, the f-stop was too high, or the shutter speed was too high.

I suspect it was a combination of those things... since it ranges from difficult to impossible to put filters on a fisheye (and certainly not a matte box), I'm betting that to prevent overexposure both the f-stop was increased too high and the shutter speed was cranked up. That would definitely give you the visible grain.

I have a 8mm MC Peleng fisheye lens that I have used with the Mini35 without trouble, but you do have to be careful with it.

As far as removing it, the suggestions given so far are excellent.

As far as Monday-morning-quarterbacking goes and prevent it from happening again... I would say the shooter needs to make sure he is using a real monitor, and not relying on the camera viewfinder (which will not show the grain), and tweak the speed of the groundglass accordingly. Keep the iris pretty wide and the shutter speed "normal" (1/48th if shooting 24p). If overexposure is a problem, most fisheyes will take rear-of-the-lens filters, I would try some ND back there. And... since fisheyes tend to have such infinite depth-of-field, I would explore whether using the DoF converter is even necessary at all with these particular kinds of shots.


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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Sean ONeil
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 5:22:50 pm

Thanks everyone for the advice. The shooter shot at 60fps, not 24, since this is sort of like a virtual reality type deal. Perhaps the lens adapter could not keep up with that shutter speed. Shooting 60fps was actually my suggestion during pre-production, but I never realized what was involved in putting a 35mm lens on an HD camera (not that it's my job to know this, I'm just an editor). I assumed the adapter was simply a different physical locking mechanism. I had no idea there were extra pieces of glass that fricking spin!?! Next type we'll make sure they use an HD lens instead of 35mm adapter.

Sean


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Todd Terry
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 5:39:56 pm

[Sean ONeil] "The shooter shot at 60fps, not 24,"

Ahhh... I'm betting that's your problem. I didn't realize you were shooting slow-mo footage, which brings its own set of challenges. With 60fps with the Varicam then your shutter speed was probably 1/120th or maybe even higher. A speed that high allows the shutter to "freeze" the grain pattern on each frame, rather than invisibly blur it out the way that it should.

Actually I had forgotten that you said you were shooting Varicam. I was thinking that it was probably shot with a smaller camera and a not-so-good lens converter. But with Varicam the converter was most likely a P+S Technik Pro35 (I don't know of any of the cheaper converters that will even fit a Varicam, they are all for 1/3" cameras).

If that was the case, I'm betting it was an early-model Pro35, which used a spinning groundglass... newer units from P+S Technik have an oscillating groundglass that avoids those "swirls" problems. Earlier models also didn't have continuously-variable speed controls (I think it was just "high" and "low," if I recall), so it might not have been possible for the operator to adjust speed well enough to dial out all of the grain. At 60fps it should probably be set to its absolute fastest position anyway.

If you do this again and need to use a lens converter (if, say, you must use the PL mount fisheye because you can't find a native fisheye for the Varicam), try to get your hands on a current series Pro35... there's a big rental market for them so they should be available (otherwise, it's cough up $25K to buy one).


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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Sean ONeil
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 6:00:26 pm

This is great information, thanks! I believe it was a P+S Technik.

What seems odd to me is that prior to 2000 or so, just about every single NTSC video camera ever made only shot at 59.94 fps (interlaced, but still the same shutter speed). One would think an old lens adapter would be designed for this, rather than newer video cameras capable of a film frame rate.

Sean


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Todd Terry
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 6:16:28 pm

[Sean ONeil] "What seems odd to me is that prior to 2000 or so, just about every single NTSC video camera ever made only shot at 59.94 fps"

Well, 59.94 FIELDS per second is different than 59.94 FRAMES per second. Those old NTSC cameras were still shooting a "normal" shutter speed of 1/60th.

When you get into 1/120th (or higher) territory your video definitely begins to take on the same choppy stuttery look as when film is shot with a narrow shutter (with variable-shutter film cameras). Then your video begins to look a lot like "Gladiator" or "Saving Private Ryan."

Lens converters (well, good ones... and the P+S Technik is a great one) work pretty darn flawlessly at 24p (and 60i, for that matter) when shooting with "normal" shutter speeds. But they have fairly narrow paremeters in which they excel. It's usually when you push those boundaries (with f-stops too high or shutter speeds too fast) that you get into trouble.


T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com






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Sean ONeil
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 7:19:19 pm

I think shooting 60p one would still normally uses a shutter speed of 1/60th, same as NTSC 60i. 60p simply captures the whole frame once per exposure as opposed to one field per exposure. Using 1/120 wouldn't make sense unless you were trying to shoot "120i" or something like that... I just looked at the Pannasonic page for the camera and it says 1/60th exposure time is the shutter speed for 60p.
http://catalog2.panasonic.com/webapp/wcs/stores/servlet/ModelDetail?display...

Anyways, he probably had it dialed in for 24, which of course would screw it up either way. Thanks again for your help. We definitely won't be making the same mistakes again!

Sean


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Richard Herd
Re: Help An Editor Identify This Problem?
on Sep 8, 2008 at 11:54:50 pm

That raises a fine question all around:

Film is shutter angle * frame rate = shutter
180/360 * 1/24 = 1/48.
Piece of cake and accounting for my film speed, I can get an exposure.

Video is what?
"Synchro" rate * sampling frequency = Huh?

I have no idea what the equivalent equation is, and it'd be great if someone could cut through the murk.





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Sean ONeil
Re: Help An Editor Identify This Problem?
on Sep 9, 2008 at 12:29:09 am

I think the difference is that video cameras don't have an actual real shutter. It's just an electronic process that mimics one to control motion blur.

Sean


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Richard Herd
Re: Help An Editor Identify This Problem?
on Sep 9, 2008 at 4:27:40 pm

An equation would be nice.



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grinner hester
Re: Help An Editor Identify This Problem?
on Sep 28, 2008 at 10:03:10 pm

after ya fire the photog, just runb out with yer camera and cappture what ya need.
You'll find over and over you as an editor are in a better seat to grab what is needed than a news photog seeing himself as a DP.
these are budget eaters, in my book and you can easily scoop up the entire production next time around.



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Sean ONeil
Re: Help An Editor Identify This Problem?
on Sep 28, 2008 at 10:35:59 pm

What?

Sean


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grinner hester
Re: Help An Editor Identify This Problem?
on Sep 29, 2008 at 1:58:32 am

depend on others less and yourself more often.
it's both cooler and more billable.



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Sean ONeil
Re: Help An Editor Identify This Problem?
on Sep 29, 2008 at 5:42:22 am

I can't tell if you're being sarcastic or not.

Sean


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