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Sony HVR-V1 / HDR-FX7
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Old March 30th, 2007, 12:47 AM   #1
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V1 progressive: stuttering vs strobing

Since the V1E is my first progressive camcorder, I'd like to avoid mistakes and misconceptions and ask my more knowledgeable friends here: am I right thinking that too slow a shutter speed of a progressive video will cause stuttering, and too high shutter speed (just like with any video) - strobing effect. Now, what is the best compromise for the least eye-fatiguing, most fluid motion progressive? One would think that - since film is 24 fps with 1/48th shutter - the same should be best for progressive video (with 25fps and 1/50th for PAL, of course). If so, why does changing mode from interlaced to progressive switch the camera to 1/25th by default (the same is true with the Canon A1)?

Also, what does the theory say about how watching 25fps on a 60 Hz (rather than 50, or 100 Hz) LCD affect fluidity?

Speaking of the V1, one more question: do you guys also find the direction of the zoom and focus rings awkward? Zoom for instance; when I go tele, I'd tend to think (feel?) I should "turn in" rather than "turn out"... This is customizable with the Canon, but not with the V1:(
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Last edited by Piotr Wozniacki; March 30th, 2007 at 03:37 AM.
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Old March 30th, 2007, 05:23 AM   #2
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Piotr,
there's no simple answer to this question although you're indeed going down the right path factoring it in as many seem to have come unstuck on this. The complete answer involves a lot, much of which I am far from an expert on, other than to know how involved a complete answer is. I'd suggest doing some research, the ACS has detailed information on this topic. I can say this though, there's no one simple shutter speed setting to keep you safe, you need to factor in many things.

For a more 'filmic' experience you can get the V1 to set shutter speed as shutter angle, that's typically how it's defined in a film camera. I guess Sony and Canon chose a 360 deg shutter as the setting most likely to keep you out of harms way.
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Old March 30th, 2007, 05:28 AM   #3
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Bob, thanks for your answer; may I know what ACS stands for (apart from Australian Computer Society:)?
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Old March 30th, 2007, 06:20 AM   #4
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"am I right thinking that too slow a shutter speed of a progressive video will cause stuttering, and too high shutter speed (just like with any video) - strobing effect."

I wouldn't call slow shutter speed "stuttering". A slow shutter will cause smearing because moving objects will have traversed across the image too much during the time of the exposure. A certain amount of motion blur (smearing) is natural as our eyes also have motion blur. Move your hand really fast in front of your face and it will turn into a blur. It is acceptable to have some blur, but 1/25th shutter is getting to be such a long period of time that the motion blur may be unacceptable. The reason that switching from 30i to 24p would switch from 1/60 to 1/24 is that 1/60 is constant exposure when dealing with interlaced frames. Constant exposure of 24fps progressive is 1/24th shutter which, as Bob said, 360 degrees of shutter.
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Old March 30th, 2007, 07:03 AM   #5
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Originally Posted by Marcus Marchesseault View Post
I wouldn't call slow shutter speed "stuttering". A slow shutter will cause smearing because moving objects will have traversed across the image too much during the time of the exposure. A certain amount of motion blur (smearing) is natural as our eyes also have motion blur. Move your hand really fast in front of your face and it will turn into a blur. It is acceptable to have some blur, but 1/25th shutter is getting to be such a long period of time that the motion blur may be unacceptable. The reason that switching from 30i to 24p would switch from 1/60 to 1/24 is that 1/60 is constant exposure when dealing with interlaced frames. Constant exposure of 24fps progressive is 1/24th shutter which, as Bob said, 360 degrees of shutter.
Markus, I agree that anything slower than 1/25th would cause smearing rather than stuttering. But you seem to contradict yourself when saying that 1/25th will create unacceptable motion blur, and later (indirectly) - that 1/25th constant exposure is appropriate for 25p. Or am I missing sth?
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Old March 30th, 2007, 04:17 PM   #6
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I think I'm confused, too.

I was going to say that frame rate and shutter speed are two independent settings. But I'm not sure that's completely true.
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Old March 30th, 2007, 05:18 PM   #7
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Originally Posted by Doug Graham View Post
I think I'm confused, too.

I was going to say that frame rate and shutter speed are two independent settings. But I'm not sure that's completely true.
They ARE 2 independent settings, but humans find a relation between them.

Frame rate determines temporal sampling. Folks have used 16fps to over 60fps. Rates below 50fps can NOT capture reality. They render motion poorly. It's like audio sampled below 20kHz. The lower the rate -- the worse the motion is accuately captured.

The fact that film was expensive -- ment that lower rates were used. We have gotten used to the poor motion rendition and have enshrined it -- at 24fps. So folks want to shoot 24fps even through it does a poor job with motion. They would argue that the very fact that motion is NOT captured accurately is what allows us to "suspend disbelief" and enter into the story. I think this theory is at least culturally true. The fact that narratives are shot using 60i in Asia -- says it may not be universal.

Frame time works exactly like shutter-speed on a still camera. It determines how much motion blur is captured. We all know that 1/50th second is the point at which "normal" motion becomes visibly blurred. (There's a calculation one could do of the subject's motion vector and the amount of movement captured over a specific time.)

This is why folks shoot stills at 1/50 to 1/60th second OR faster.

The 1/50th value captures a bit of blur which it turns out helps tie one movie frame to the next. Blur helps overcome the defect of low temporal sampling. And, wonderfully, 1/48th was a 180-degree shutter at 24fps.

Longer than 1/48th and there is more blur. My rule, doubling the exposure time is the limit. At this point, the blur is artificially too much. You are now creating an FX.

Shorter than 1/48th removes the blur entirely which causes each frame to stand alone. My rule, halving the exposure time is the limit. At this point, blur is artificially too little. You are now creating an FX. (The Saving Private Ryan strobe look.)

Thus, once you have chosen a frame rate -- shutter-speed varies from BLUR to STROBE.

PS: I've left out the eye-tracking artifact which causes the appearance of 2 displaced objects when 25 is displayed at 50 or 30 is displayed at 60. Or, 24 at 48. Blur can help overcome this eye artifact. Which is why 720/30p was often shot with a 1/30th shutter. We accepted "too much blur" to overcome "too much strobing" at 1/60th. That's why I use 216 not 180 with 24p.
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Old March 30th, 2007, 07:18 PM   #8
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Originally Posted by Piotr Wozniacki View Post
Bob, thanks for your answer; may I know what ACS stands for (apart from Australian Computer Society:)?
Sorry,
always get it wrong, try:
http://www.theasc.com/


ACS = Australian Cinematographers Society
ASC = American Society of Cinematographers
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Old March 31st, 2007, 03:06 AM   #9
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Originally Posted by Bob Grant View Post
Sorry,
always get it wrong, try:
http://www.theasc.com/


ACS = Australian Cinematographers Society
ASC = American Society of Cinematographers
Bob, my bad - I should have guessed, or googled more thoroughly:)

Digging deeper, and complicating things even more: do you think that keeping the 1/60th shutter speed as an available choice on PAL cameras, the manufacturers are suggesting to actually use it in spite of 25 fps, for the sake of better "synchronizing" with the 60 Hz refresh rate of most LCD monitors? Because other than that, I can't find a reason why this speed (standard for NTSC) should be used for PAL. You R60 guys don't have 1/50th available on your cameras, do you?
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Last edited by Piotr Wozniacki; March 31st, 2007 at 05:30 AM.
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Old March 31st, 2007, 06:12 AM   #10
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As far as I know shutter speed will not affect syncronising directly, it's frame rate that you'd need to change. Shutter speed (or angle) only affects how motion looks, frame rate determines the 'resolution' of motion, shutter speed determines the 'look' of motion.
One tip though, if you intend to slomo or motion stabilise footage in post a faster shutter speed helps quite a bit.
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Old March 31st, 2007, 10:22 PM   #11
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Originally Posted by Piotr Wozniacki View Post
Markus, I agree that anything slower than 1/25th would cause smearing rather than stuttering. But you seem to contradict yourself when saying that 1/25th will create unacceptable motion blur, and later (indirectly) - that 1/25th constant exposure is appropriate for 25p. Or am I missing sth?
That's not what I was saying. I actually think 1/25th shutter is too slow. I have tested 1/30th at 30p and it is passable. I don't think there is any reason for most people shooting on HDV to try to be compatible with a "filmout" because there really is no reason. Most film festivals should be able to project HD, if not now, soon. Therefore, I am not really concerned with 24p and think that 1/24th (360 degree shutter) is a bit much at that slow shutter speed. I agree that 1/48th is about right to get a natural amount of motion blur. 1/60th isn't that far from 1/48th to be too concerned. I really like the idea of 60p at 1/60th for capturing every moment at a high framerate.

What I wish is that someone would have had the brains to set 48p as an option as it would have better motion rendition and keep compatibility with 24P film. It would simply double the frames at the same exposure time to retain similar motion rendition while significantly improving smoothness of motion. It could also be used as an overcrank for 24p projects. The HVX200 does something like this, but only at 60p. 48P should have made everyone's lives easier as both film and digital projection would be accounted for without pulldown and motion rendition confusion.
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