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Old March 11th, 2006, 03:07 AM   #1
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Should shutter speed always be double?

Hi,

Here is a total newbie question about my HD100. Iím noticing people generally use twice the shutter speed that they are capturing to tape. 24p at 48, 30p at 60 and so on. Is there a good reason for this? Why not set the shutter at the same frame rate that you are capturing to tape?

I understand the higher shutter speed gives a crisper look but what if you are shooting an event at night with nothing but your camera light? The lower shutter speed is much brighter but will this create a strobe/choppy effect?

Thanks,
Scott
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Old March 11th, 2006, 08:33 AM   #2
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You get more motion blur the longer the shutter. The 180 degree shutter (1/48th for 24 fps) is traditional from film.

http://en.wikipedia.org/wiki/Shutter_angle
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Old March 11th, 2006, 08:58 AM   #3
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Tim is right. The standard shutter position in a motion picture camera is 180°. Therefore, exposure time is always half of the frame rate.
Setting the exposure time to equal the frame rate would be physically impossible in the world of film because that would equal 360° (or 0°) shutter angle and there would be no opportunity for each film frame to advance through the gate. This also causes excess "blurriness."

This doesn't mean you shouldn't set the shutter to 1/24 when shooting 24P. It can be useful for "effect," but it is a tell-tale sign that your film was shot using a video camera. (ie: Taxi scenes in Collateral, Miami Vice)
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Old March 11th, 2006, 09:23 AM   #4
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Part of the reason you'd want to stick with these rules is so your work looks comparable to to what viewers expect under similar conditions, etc. When you understand what has been done for years and why, THEN you can break the rules.

Say you're shooting something that's supposed to look like a news reporter standing in the rain reporting. That exact situation for eons has been shot by news videographers at 30fps interlaced, with a 60th shutter. If you shoot 30th shutter, it will look completely different.

Just be aware that it's not a purely technical choice. Many camera settings affect the look in subtle ways that are picked up by viewers who have been watching TV their entire lives...and carry certain messages and context.
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Old March 11th, 2006, 10:31 AM   #5
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why isn't 60p or 60i then shot at a shutter speed of 120?
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Old March 11th, 2006, 11:11 AM   #6
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Quote:
Originally Posted by Thomas Smet
why isn't 60p or 60i then shot at a shutter speed of 120?
Because 60i is the same as 30fps in NTSC, therefore 1/60th shutter is the norm, and has been for years. 1/50th is the norm for PAL (25fps) 50i as well.

shooting and broadcasting 60P creates, in essence, the same temporal motion as 60i, so the same shutter should be used (live broadcast of the Superbowl for example.)

However, if you are shooting 60P as a way to capture overcranked slow-motion, then by all means use 1/120 (or at least 1/100) to achieve good sharpness on each frame.
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Old March 11th, 2006, 11:11 AM   #7
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A film camera with a 180 degree shutter only records to film half of everything the lens sees. This is then projected with a 270 degree shutter (to maximise the light on screen) and this frame is then reprojected a second time before the next frame is pulled into position, and so on. This happens 24 times per second.

No wonder the film look is all jerks and stutters - nothing is real-time. Video is different. If you film with a shutter speed of 1/50th (PAL) you record to tape everything that happens in front of the lens (minus a miniscule amount where the CCD charge is released and re-cycled for the next field). This footage is then shown on a TV (most of which have considerable screen persistance due to phosphor decay and LCD hysteresis) and you get to see life as it really happened, with nothing cut out, deleted or flashed twice at you.

I'm one of the few that seem to much prefer this silky, creamy motion smoothness, coming as it does with 50 different (half resolution) pictures per second. Remember that the film look was born out of necessity ~ it's a historical and mechanical interpretation of what was possible back in the days of chemical photography. If they could've had video smoothness for their camera and subject motion, they'd have leapt at the chance.

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Old March 11th, 2006, 11:44 AM   #8
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Quote:
Originally Posted by Tom Hardwick
Remember that the film look was born out of necessity ~ it's a historical and mechanical interpretation of what was possible back in the days of chemical photography. If they could've had video smoothness for their camera and subject motion, they'd have leapt at the chance.
Actually, it was interlacing that was born out of necessity.
24fps on film was established as the threshold at which humans percieve motion (originally it was 18fps) so the logical conclusion was to photograph and project 24 fps.

The first TV systems, using the same logic, were actually progressive scan, but because the refresh rates weren't high enough, there was a phenomenon during panning called "ripping." It meant that objects would appear to skew as the camera panned. For example, a flag pole would suddenly appear to be on a 45° angle while the camera was panning and then become upright in the static shot.
The engineers' solution was to split the workload and do two half scans - which became known as interlacing.
60Hz was chosen in North America because that was the frequency of AC power (which was originally used to clock the cycles) and 50Hz was chosen for Europe for the same reason.
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Old March 11th, 2006, 01:25 PM   #9
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Quite correct Tim - interlacing was born out of necessity as well. We do live with a load on our shoulders passed on to us by the pioneers.

The ripping you describe has a similarity to the 'elliptical wheels' of those early films, too. As all movie cameras use focal plane shutters rather than interlens shutters as on still cameras, the top of each frame wasn't exposed at the same time as the bottom of the frame. So when a wheeled vehicle moved across the frame, the top of the wheel was exposed before the bottom of the wheel, thus turning it into an ellipse on screen.

Now of course we get our ellipses for free. I cannot count how many homes I've been into where the 16:9 TV is set on some ludicrous 'expand' setting, and 4:3 original footage is distorted to high heaven. This often distorts the image more at the edges of the frame while at the same time masking out top and bottom, simply because the TV owner has paid for all that screen real-estate, and by golly he's going to fill it.

tom.
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Old March 12th, 2006, 09:14 AM   #10
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shutter speed for film-like footage

So in PAL land, when wanting to shoot 25p and trying to get the film-look with medium motion (no action, but like your usual music video movement), what is the appropiate shutter speed?

Also, if I have a scene that I want to do slow-mo (in post), what is the best shutter speed in 25p/25i?

Thanks

- Nima Taheri
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Old March 12th, 2006, 10:03 AM   #11
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Do you mean 25p/50i? Whatever, if you film everything at 1/50th you'll have filmed everything that happens in front of your lens. As the slow motion program is trying to 'make something out of nothing', I find it works best if you give it more to play with up front. If you shoot at 1/150th sec, say, then you've only filmed 1/3rd of everything that happened, and any interpolation has to make wilder guesses at the intermediate, made-up frames.

But the really great thing about video is how quick and easy it is to experiment. Learning has never been so quick and easy, so go out there with your camera, speak into the mics as you do it, and come indoors to have a look at what you've got.

tom..
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Old March 12th, 2006, 05:12 PM   #12
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HD100 Shutterspeeds

Is it just me or are the shutterspeeds on this camera a bit... well not right...? Ok when ever I push the shutterspeed past 1/48th it gets especially juddery and stacato looking, obviously puting a camera to higher shutter speeds will do this but when looking at the footage as compared with any sony cam at a high shutter speed the JVC seems to loose the 24p fluidity... it seems to degrade into some bunk webcam type of mode if I shoot at say 1/100th and do a pan... I like high shutter speed photography but also I heard that when shooting at higher shutter speeds it shortens the depth of field makes it more shallow than if you were to have a slow shutter speed like 1/24 1/48... Why is it that the high shutter speeds on this camera are so poor... I know you can turn on motion smoothing but that looks terrible as well, then there are trails and artifacts in the video... does anyone have any advice on the matter? Why is it that the higher shutter speeds on this camera as compared to say an FX1 or VX2000 are so much more STACATTO and seemingly affecting the 24p cadence... have other users made similar observations? What are your thoughts and advices? Also is it true that shooting at a higher shutter speed creates more shallow depth of fields?
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Old March 12th, 2006, 06:22 PM   #13
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Quote:
Originally Posted by Bruce Meyers
Is it just me or are the shutterspeeds on this camera a bit... well not right...? Ok when ever I push the shutterspeed past 1/48th it gets especially juddery and stacato looking, obviously puting a camera to higher shutter speeds will do this but when looking at the footage as compared with any sony cam at a high shutter speed the JVC seems to loose the 24p fluidity... it seems to degrade into some bunk webcam type of mode if I shoot at say 1/100th and do a pan... I like high shutter speed photography but also I heard that when shooting at higher shutter speeds it shortens the depth of field makes it more shallow than if you were to have a slow shutter speed like 1/24 1/48... Why is it that the high shutter speeds on this camera are so poor... I know you can turn on motion smoothing but that looks terrible as well, then there are trails and artifacts in the video... does anyone have any advice on the matter? Why is it that the higher shutter speeds on this camera as compared to say an FX1 or VX2000 are so much more STACATTO and seemingly affecting the 24p cadence... have other users made similar observations? What are your thoughts and advices? Also is it true that shooting at a higher shutter speed creates more shallow depth of fields?
Bruce, I merged your post into this thread because it deals with the same topic.

First off, shutter speed does not affect DOF in any way. Maybe you have auto iris on and therefore increasing the shutter speed causes the iris to open up to compensate for the light-loss and you are seeing the shortening of DOF.

The only factors in DOF calculation are focal length, focus distance, aperture (aka iris), and the "circle of confusion." CCD size doesn't even affect DOF calculations, only your choice of focal length for any given FOV. More info here, here and here.

As for your questions of increasing shutter speed: There is nothing wrong with the way the shutter works on the HD100. The difference you are seeing between it and the FX1 or VX2000 is that the HD100 shoots progressively, just like film.

I'd like you to watch the first 10 minutes of Saving Private Ryan (Normandy Beach assault) and compare the "stacatto" look of that scene to the HD100 at a shutter speed of 1/100. Janusz Kaminski used a 90° shutter angle in most of those shots, which equals 1/96th second exposure time.
I think you'll find that the HD100's shutter captures the same way with predictable results.
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Old March 12th, 2006, 06:24 PM   #14
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>Is it just me or are the shutterspeeds on this camera a
>bit... well not right...?

It seems fine to me.

>Ok when ever I push the shutterspeed past 1/48th it gets
>especially juddery and stacato looking, obviously puting a
>camera to higher shutter speeds will do this but when
>looking at the footage as compared with any sony cam at a
>high shutter speed the JVC seems to loose the 24p
>fluidity...

The Sony cams won't do 24p, so a higher shutter speed on them will certainly be different than on a camera that does 24p. If you really want to compare, set the JVC to 60i.

>Also is it true that shooting at a higher shutter speed
>creates more shallow depth of fields?

No.
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Old March 12th, 2006, 06:30 PM   #15
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I'm going to say the same thing as Tim D and G., just in a different way.

The slower the frame rate, the more a higher shutter speed will seem "stacatto". A camera that shoots 30i (which is 60 individual images a second) at 1/120th shutter speed is still shooting more than twice as many images per second as a 24p camera using the same shutter speed. This creates smoother motion, and lessens any strobing effect.

There's nothing wrong with the shutter speeds on the HD100. They behave as any other 30p or 24p camera, whether that's a DVX100 or F900. If you think it's different, then you're seeing the effects of other variables.
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