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Strobes


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#1 Phil Rhodes

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Posted 11 October 2007 - 12:41 PM

Hi,

Watch this video:

http://web.mac.com/f.....d Camera.html

Step through the strobe flashes frame by frame.

This is why we do not use rolling shutters (much) on digital cinematography devices.

Phil
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#2 John Sprung

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Posted 11 October 2007 - 01:01 PM

Clearly what is needed here is a way to synchronize the strobes with the Red camera. There are some cases in which the strobe covers the whole frame, we just need a sync pulse to trigger it that way every time. For gunshots, I don't see why the same slow burning blanks we use for film wouldn't work.

This is an issue that needs to be addressed, but probably way far down on the priority list. Definitely not a killer for the vast majority of production.





-- J.S.
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#3 John Peters

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Posted 13 October 2007 - 11:10 AM

rolling shutter is typical for CMOS, not that of a big deal
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#4 Jeremy M Lundborg

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Posted 25 January 2010 - 11:23 PM

Clearly what is needed here is a way to synchronize the strobes with the Red camera. There are some cases in which the strobe covers the whole frame, we just need a sync pulse to trigger it that way every time. For gunshots, I don't see why the same slow burning blanks we use for film wouldn't work.

This is an issue that needs to be addressed, but probably way far down on the priority list. Definitely not a killer for the vast majority of production.




I'm curious as well. I am interested in using photo strobes to emulate photographic flashes on the cheap. Shooting with the RED I have rolling shutter concerns but have not been able to test as of yet. All that despite having a project looming which will require said effect.

I would appreciate any advice on the matter from people with more experience.
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#5 John Sprung

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Posted 26 January 2010 - 02:52 PM

If you can't sync the strobes, shoot without them and fake it in post. You just have to hand-lighten stuff in individual frames. If you plan for it, you can do single frame events with some power windows in color timing. With more money, you can roll out the bigger effects guns.





-- J.S.
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#6 Adrian Sierkowski

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Posted 26 January 2010 - 02:55 PM

What about those old photo-bulbs? The ones which had what looked like wire-mesh inside of them? I haven't seen one in a LONG time, but from what I recall they flash and burn off slower than a new-er flash. Also is a bit warmer in color, says me. Might help to spread the flash out across a whole frame or two on a CMOS camera.
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#7 Mathew Rudenberg

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Posted 26 January 2010 - 03:51 PM

What about those old photo-bulbs? The ones which had what looked like wire-mesh inside of them? I haven't seen one in a LONG time, but from what I recall they flash and burn off slower than a new-er flash. Also is a bit warmer in color, says me. Might help to spread the flash out across a whole frame or two on a CMOS camera.


If you can afford it lightning strikes makes a small unit (called a 'paparazzi' I believe) that stays on for a minimum of 1/24th of a second, and thus shouldn't cause any rolling shutter artifacts... I think

Ironically the CMOS rolling shutter is similar in some ways to a spinning shutter on some film cams. I remember a colleague of mine shooting 16 with a short duration wild strobe and on many of the frames it froze the shutter so only part of the frame was affected. It was very noticeable when the strobe was the only source of light.

One other question to ask yourself is just how pervasive will the flashes be? If there are just a few and your budget is low can you live with some partial frame flashes? Personally I find that less distracting than a cheap post flash effect, and while the DPs watching your film may cry foul, most people probable won't notice.
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#8 Chris Millar

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Posted 26 January 2010 - 09:21 PM

Have a look at the off-topic chat in this thread:

http://www.cinematog...h...&hl=strobes

;)
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#9 Phil Rhodes

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Posted 27 January 2010 - 08:27 AM

If you can afford it lightning strikes makes a small unit (called a 'paparazzi' I believe) that stays on for a minimum of 1/24th of a second, and thus shouldn't cause any rolling shutter artifacts... I think


It can still start up halfway through the frame.

Anything that happens quickly can cause artifacts with a rolling shutter. I suspect an old magnesium-style flashbulb might do a bit better, but you'd want to test - I'd be worried that the fast (though not anything like as fast as a xenon flashtube) might cause a gradual increase in brightness down the frame, which might look just as bad.

P
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#10 John Sprung

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Posted 27 January 2010 - 02:25 PM

We've done lots of these in post. They definitely don't look cheap, most people don't even know that they're done in post. Absolutely a better result than those half and half frames that anybody can see are wrong. If they look obvious, you're at the wrong post house.





-- J.S.
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#11 Phil Rhodes

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Posted 27 January 2010 - 06:13 PM

Got any examples?
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#12 Mathew Rudenberg

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Posted 27 January 2010 - 08:26 PM

We've done lots of these in post. They definitely don't look cheap, most people don't even know that they're done in post. Absolutely a better result than those half and half frames that anybody can see are wrong. If they look obvious, you're at the wrong post house.





-- J.S.


When I said 'cheap' I meant one not done by an experienced and thus generally more expensive post house - I certainly don't mean to malign your work, which I'm sure is of the highest quality.

Phil, if it's a 24th of a second and it starts halfway down the frame does that mean that the next consecutive frame has the other half flashed? What would that look like?
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#13 Phil Rhodes

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Posted 28 January 2010 - 04:30 AM

Phil, if it's a 24th of a second and it starts halfway down the frame does that mean that the next consecutive frame has the other half flashed? What would that look like?


Something like that, depending on exact timings - bear in mind the "shutter" is only supposed to be open for half the time normally so the shutter period would eat a bunch of the flash. I suspect the answer is "not very nice".

P
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