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Old January 28th, 2008, 10:09 PM   #1
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30p is the new 24p - HVX200 & HPX500 motion

We've all assumed that to really create the "film look" with a video camera that you'd need to emulate all film-cameras settings to achieve it, from shutter speed (or shutter angle) to gamma/color settings etc.

Granted, achieving a good film-like output from any camera is much more than just a few settings, it's also lens work, lighting and of course proper composition but, the end result isn't always as expected and here's what I mean:

Recently I shot some same-scene test footage from the HVX200, HPX500, and an Aaton and Arri 35mm film cameras with "normal" lenses specifically to try to get match more of a true film-like output - from the perspective of motion - from the 200 & 500 and the results were really surprising. We setup all the lenses so they closely matched each other with respect to focal length and field of view to prevent any exaggeration - or lack of - due to a focal length mismatch.

Keep in mind, that since all video cameras do not have a physical "shutter" to speak of; shutter speed or angle is actually *simulated* by how the imaging chips actually capture the image, so the end result of all this simulated operation can't actually look exactly like it's a film camera, because it's not.

The scenes that were shot were very basic; a "talking-head" model with a lot of hand gesturing, a model walking towards and away from the camera, and a model riding a bicycle past the camera.

When 24th sec shutter OR 180-degree angle (film-cam mode) was selected the video cameras - the 200 and 500 - had much more motion blur than the film cameras (film camera results viewed both projected and after x-fer to Final Cut). BUT, if we selected 30p in both the HVX200 and HPX500 then the motion blur was near-identical to that of the film cameras.

The reason I did this test, was because I had noticed many times from various projects shot with the 200 or 500 that any motion blur seemed to be exaggerated compared to what I've seen with film. I had thought that possibly something was done incorrectly either in-camera or in POST that was creating this added motion blur, but this test proves that's not the case.

For whatever reason (at least with these 2 cameras) 24p or 180 deg angle - which is technically accurate from an exposure value perspective - simply does not capture motion in exactly the same manner as film does with the same shutter or angle settings. The EV (exposure value) was correct as verified by the footage compared side-by-side but the apparent motion blur was not at all the same.

I'm not a technical guru with respect to exactly how and why video cameras work by any stretch of the imagination so I cannot offer any solid explanation as to why this behavior exists, I can only relate what we saw in the end result. I also cannot comment on how other cameras will compare; both the Varicam and the HPX2000 that were supposed to be part of this test were not available in time for this test.

The short version: If you want your HVX200 or HPX500 to have the same motion blur effect as a true film camera, shoot at 30p, not 24p or 180 deg angle.
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Old January 28th, 2008, 11:04 PM   #2
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Interesting stuff, Robert.

Note that the reduced motion blur would making keying easier as well, in the cases where that's the goal.

Is there no way to reduce the shutter time and match the motion blur without causing other non-filmlike artifacts?
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Old January 29th, 2008, 04:05 AM   #3
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Still, Robert, for film out, if you go 30p, you'll be in trouble. Lot of post work on the Telecine/filmout process!
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Old January 29th, 2008, 07:36 AM   #4
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Originally Posted by Sergio Perez View Post
Still, Robert, for film out, if you go 30p, you'll be in trouble. Lot of post work on the Telecine/filmout process!
Likewise for "world" compatability 24p can be shown easily in 50Hz countries with a 4% speed up - as happens with film at the moment - 30p won't translate as satisfactorily.
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Old January 29th, 2008, 08:10 AM   #5
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No doubt if the intent is to do a film transfer then you'd have no choice but to shoot 24p (or PAL 25p as many film projects with heavy compositing work do).

This test wasn't designed to replace workflows, simply to find a way to correctly emulate film-like motion blur in these video cameras. For 90% of the HVX/HPX users this will help their stand-alone productions, whether it's destined for DVD, web or broadcast to be more visually appealing.
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Old January 29th, 2008, 08:58 AM   #6
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As Jon asked, why not stay w/ 24p & reduce the "shutter angle"? Frame rate is in the "happy zone" & the decreased exposure time reduces blur.
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Old January 29th, 2008, 09:27 AM   #7
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That is what I would ask.

If motion blur is the only difference, then maybe a different shutter setting would do the trick?
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Old January 29th, 2008, 10:52 AM   #8
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Originally Posted by Bob Woodhead View Post
As Jon asked, why not stay w/ 24p & reduce the "shutter angle"? Frame rate is in the "happy zone" & the decreased exposure time reduces blur.
It's impossible to explain without sample imagery why this isn't an appropriate solution; try it on your own camera and watch the footage in POST, you'll see what effect speeding up or slowing down the shutter/angle does at 24p.
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Old February 2nd, 2008, 01:31 PM   #9
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Originally Posted by Robert Lane View Post
When 24th sec shutter OR 180-degree angle (film-cam mode) was selected the video cameras - the 200 and 500 - had much more motion blur than the film cameras (film camera results viewed both projected and after x-fer to Final Cut). BUT, if we selected 30p in both the HVX200 and HPX500 then the motion blur was near-identical to that of the film cameras.
Quote:
For whatever reason (at least with these 2 cameras) 24p or 180 deg angle - which is technically accurate from an exposure value perspective - simply does not capture motion in exactly the same manner as film does with the same shutter or angle settings. The EV (exposure value) was correct as verified by the footage compared side-by-side but the apparent motion blur was not at all the same.
Interesting, Robert, but I'm slightly puzzled with the way some of this is described. In the first paragraph above you mention "24th shutter or 180d". In the second you mention "24p or 180d".

First of all, I assume you know that 1/24th shutter and 24p are separate, unrelated settings.

As for manually slecting 1/24th shutter at 24p, the exposure time becomes *twice* as long as at 180d, and will thus create lots of motion blur, just as speeds below 1/30 would tend to risk blur in a handheld still camera. 1/24th at 24p means the shutter, for all intents and purposes, never closes.

On the HVX at a frame rate of 24p, 180d is equivalent to 1/48th shutter, and thus has half the motion blur tendency of 1/24th.

1/24th shutter should never be used unless light conditions force it (and there always it's much preferred to get more light if at all possible), or for very still, near-static shots. It's very easy to see motion blur artifacts with even small amounts of subject or camera movement at 1/24th. It's *much* less at 24p/180d.

Furthermore, 180d will always be half of whatever frame rate you've selected. So at 30p it's 1/60th, and at variable frame rates it likewise stays at half the frame rate, so 48p is 1/96th and so on.

In your quoted paragraphs, it could be incorrectly inferred that either 1/24th and 24p are the same, or that 1/24th and 180d are the same (at 24p). Perhaps you didn't mean to give that impression but I thought it woth mentioning.

If your tests did indeed find that an HVX set to 24p/180d has more motion blur than a film camera set identically, then that would take some explaining technically, since they're actually doing the same thing.

For myself, I've noticed much more of a sense of motion blur viewing my 24p/180d HVX footage in FCP than after going through Compressor, burning it to a DVD and viewing it on my 42" Plasma screen (I know others have reported this as well). It looks every bit as smooth there as any 35mm feature film DVD I have, which of course, being 24 frame, have a tendency to "strobe" on too-fast pans as well (as they do in theaters). The HVX does as well, to the same degree. There is evidently some difference in the way computer NLEs and LCDs handle frame rates compared to DVD players and TV sets.

On pages 13-19 of Barry Green's "HVX Book" he discusses both the strobing effect and motion blur issues, and after doing a simultaneous film camera and 24p DVX/HVX test much like the one you describe, he came to the same conclusion I have, which is that there is no difference.
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