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-   -   Slow motion question (https://www.dvinfo.net/forum/general-hd-720-1080-acquisition/92903-slow-motion-question.html)

Stuart Brontman May 1st, 2007 11:00 AM

Slow motion question
 
A client has just asked me to produce a slow motion recording of a controlled environment explosion. The explosion would be viewed at normal frame rates, then slowed down to show the instant-by-instant development of the damage being caused as the explosion continues. The client wants this shot in HD.

My question is how to do this - and if today's crop of HDV cameras is capable of this in terms of exposure (can the lens and exposure system handle the bright flash without blowing everything out) and shutter speed. I would consider the XDCAM HD as part of the group of cameras - but only for rental. The budget on this job won't justify the purchase of the XDCAM.

Thanks.

Paul Lashmana May 1st, 2007 11:29 AM

If the client expects slomo-images with a quality like in the Nike Juice It Golf Ball-ads (http://www.youtube.com/watch?v=sS8xN_S2aU0), then you should start to let him down gently, but as soon as possible. Those are made with a special camera that shoots at framerates of 1000frames/sec.

How about you film something inexpensive breaking/exploding (like an egg or a melon) or some sports, so that you can show your client what is to be expected from an HDV format? (Maybe rent or borrow a camera) And on the plus side, then you'll also have the opportunity to have your workflow in place, once the actual footage has been shot.

Stuart Brontman May 1st, 2007 12:02 PM

Explosion video
 
I think they realize not to expect miracles. They just want something usable for demonstration purposes. This is for corporate/industrial application, not high end commercial broadcast.

Due to latitude and exposure concerns from the bright explosion, this is where my camera questions come in. Can the 1/3" HDV camcorders record this type of sequence, or will I need the higher bit-rate and exposure latitude of the 1/2" XDCAM.

Paul Lashmana May 1st, 2007 12:46 PM

I'll try to film a glass being filled with a coloured fluid later tonight and then slomo it (you have a percentage in mind?). Gives me a chance to learn FCP a bit more. I'll rogepost it then up here.

I'll also film a match that's being lit by a burning candle...

Stuart Brontman May 1st, 2007 12:52 PM

I'll estimate 1/10 normal speed... Just an educated guess on what they would want to see. Since they're trying to keep corporate types interested, anything too sow or long will bore them.

Thanks for your help.

Paul Lashmana May 1st, 2007 01:01 PM

Do you have any settings in mind (I mean, like F-stops or shutter speeds) that might help me (and thus you) ?

Stuart Brontman May 1st, 2007 01:15 PM

Shutter speed of 1/120 (at least that fast) and f stop of 8 or 11...

Paul Lashmana May 1st, 2007 08:33 PM

Uploading took the best part of 90 mins, but here you have the snippets.

Filmed with an XH-A1 and edited in FCP, H.264 codec.

Besides coloured water, a burning candle and several matches, you'll also see a shameless plug for some local produce :-).

Couldn't get to 11 stops, because the canon only did 9.5.

Link: http://www.rogepost.com/n/3392885167

Kind regards,
Paul.

Marcus Marchesseault May 1st, 2007 08:48 PM

If you want to record and explosion, you will need a very high speed camera. Explosives detonate so fast that you probably won't even get one clean frame of the explosion itself. With a standard camera, the detonation will happen within one frame and motion blur will make it just look like a flash. The next frames will all be mostly of smoke rising. You might get a bit of debris for a few frames after the explosion. High explosives expand at an incredibly fast rate and a regular camera just won't get much but a flash. If you want to see the deformation of the material as the shock wave moves through the area, it won't happen with a regular camera.

"...slowed down to show the instant-by-instant development of the damage being caused as the explosion continues."

This is outside the parameters of a regular HD camera. Think of it this way, if your customer wants HD video of Pluto, you can't just go get a telephoto adapter. If you put your camera on it's fastest shutter speed, say 1/2000th of a second, you still probably won't get one good frame of the explosion. A lot of the material deformation is going to happen even before the flash. Chances are that almost all of your explosion will happen between frames at 30fps. To get the expansion of the explosion, you would probably need to be shooting at something like 10,000 frames per second or faster.

At 30fps with 1/2000 shutter, you are going to expose for .5 milliseconds then wait 29,999.5 milliseconds before doing another exposure. Chances are that all the explosion will happen for a millisecond or two during that long pause between frames. You would be lucky to get just a puff of smoke before the whole thing is over and debris is bouncing around.

Stuart Brontman May 1st, 2007 09:12 PM

Paul,

THANK YOU for the great footage. It gives me an idea of the smoothness that can be obtained with a bit of slo-mo. I really appreciate your efforts. What settings did you use in FCP?

Marcus, thanks for your input. I know, and I think the client understands there will be no miracles performed here. They already have SD footage of this explosion scenario. It was shot by someone with minimal skills and the camera setup with "auto" settings etc... This was pawned off as being done by a "professional". Needless to say, the footage looks terrible. The explosion occurs and all you see is the brilliant flash until the camera resets the aperture. That takes close to 3 seconds.

My main concern was how well an existing HDV or XDCAM HD camera would hold the image quality during the explosion. I probably didn't make that very clear in my original post. The slo-mo part is nice, but the client does not expect to see the explosion unfold in the detail level that could be obtained by such a specialized camera. The speed in Paul's example would be great for my client's purposes.

Of course, the worst part of all is the client needs this shot in two weeks. I don't even have the camera yet! Fortunately the client is paying me well for this. I'm looking at it as a way to break into HD and help offset the cost. I've spent months researching many of the 3 chip HDV cameras and the XDCAM. I'd probably look at the 3 chip Canons if I buy or the XDCAM if I rent. If these cameras can pull this off with a reasonably good image of the explosion, my client will be happy. BTW, the explosion is fairly small. It will cover an area of about 6' x 6' x 6' cube.

Stuart

Marcus Marchesseault May 1st, 2007 09:46 PM

Well, then my suggestion would be to use a fairly fast shutter and LOTS of incandescent light. Fluorescent light might flicker at super fast shutter speeds. Actually, you probably won't want to use a ridiculously fast shutter or you won't catch enough of the explosion per frame. If you use lots of light and slightly underexpose, the flash won't be as bright relative to the background.

Paul Lashmana May 2nd, 2007 03:20 AM

Thanks Marcus, for giving those hints. I wouldn't know where to start when filming such an explosion.
I already pointed out to Stuart that if his client wanted a result like the Nike golf ball ads (link included in my first post), that he should make clear to his client that that would not happen with an HDV cam.

Stuart,
I pretty much imported the footage as it was, native HD, and had frame blending checked for each slowed down clip. I tried 10% first, but that was simply unusable.

Kind regards,
PL.

Ken Hodson May 2nd, 2007 07:01 PM

I think your options would be a Varicam, HVX200, or a JVC HD200/250. All three cams shoot at 60p. I think 60p would be the single most important factor, as you are not going to want interlaced or 30p footage.

Jemore Santos May 3rd, 2007 05:44 AM

HD video at the moment will not be able to capture such speeds, best thing for you to do is hire out a more high end camera (varicam) or try getting an Arri SR2 or SR3 Hi-speed camera, I know this is a 16mm film camera, but you will be able to crank the SR cameras of upto 150fps, all at 180 degree shutter. So have a think about that option too.

Dana Salsbury May 3rd, 2007 10:14 AM

I've never messed with shutter speed on my FX1. Are you saying that if I want to shoot slow motion in HD that I won't be able to? I'm not satisfied with the choppy shots I get when I stretch a clip in Vegas7. I'd hoped to either change my cam's shutter speed or find a plug-in...let me know if you would. Thanks.


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