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Changing film speed in one take


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#1 Jason Hoffman

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Posted 25 June 2009 - 01:55 PM

I have a Bolex H16 Reflex.

Is it possible to switch between film speeds during one take?

For example, if I set my camera to 24fps, adjust the aperture accordingly and run the film, is it possible to switch to 18fps during the same scene? What is the best way to do this without compromising exposure?

thanks,

Jason
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#2 Adrian Sierkowski

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Posted 25 June 2009 - 02:51 PM

As far as I know this can't be easily done on the bolex w/o external controllers if even at all (might be some doo-dad that connects via the external motor attachment I recall H16s having on some models).
It's called Ramping, and normally you ramp speed and chance iris at the same time to compensate. It's something generally done on higher end cameras (In fact I'm not even sure how to go about something like this on my SR3)
Why not just change the camera speed to 18fps in post for the effect? You should be able to keyframe something like that in FCP/Premier/AVID pretty easily.
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#3 Jason Hoffman

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Posted 25 June 2009 - 03:18 PM

Makes sense, sounds like editing in post production is the ticket.

thanks!
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#4 Joe Zakko

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Posted 11 January 2011 - 05:57 PM

why can't it be done, one guy changes frame rate, the other changes the f-stop
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#5 Chris Millar

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Posted 11 January 2011 - 06:50 PM

Booo!!! Adrian!!
:lol:


easy peezy with two people:

24/18 - 1.33333

Log base 2 of 1.33333 = 0.415 stops

so just close the iris half a stop in sync with the speed change - no bolex prime I know has half stops marked so your guess is as good as mine and your focus pullers - in other words:

It'll be fine ...

Well, ok - yeh it depends, over what duration will the ramp occur ? You realise the speed settings don't 'switch' they are a directly continuous ramp as you move the governor radius thingybob...

And the speeds dont have witness marks on the dial for a reason, they are off! - but - the relative change of 0.415 stops should be pretty much right
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#6 Adrian Sierkowski

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Posted 11 January 2011 - 06:55 PM

My main concern with all of this wouldn't be the iris changes; but rather with whether or not doing the ramp on the clockwork camera will screw it up. I don't think it's something the designers had in mind when it came out. Now, on an electronic camera, I don't see a problem with it as much so as a mechanical one...
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#7 Chris Elardo

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Posted 11 January 2011 - 06:59 PM

It might be easier if you have the ESM motor. The speed selector knob actually clicks into position. Also you won't be timing the ramp-up within the confines of the spring motors 28 (give or take) seconds of power.
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#8 Chris Millar

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Posted 11 January 2011 - 11:23 PM

My main concern with all of this wouldn't be the iris changes; but rather with whether or not doing the ramp on the clockwork camera will screw it up. I don't think it's something the designers had in mind when it came out. Now, on an electronic camera, I don't see a problem with it as much so as a mechanical one...


There is no issue with the bolex cams that I'm aware of - you're just sliding a cam follower kind of thingy up and down the governor - sure, pedants will assert that if its spinning you'd be wearing the face of the cam thingy a little bit more than normal - if it were normal running then the face of the cam that is touching/pushing would find an equilibrium between the two sides of the cam follower (depending on which direction the speed was last set, faster or slower) - but really running and adjusting is nothing but a little more friction in the grand scheme of things

If its quick, then even less of an issue

It might be easier if you have the ESM motor. The speed selector knob actually clicks into position. Also you won't be timing the ramp-up within the confines of the spring motors 28 (give or take) seconds of power.


28 secs is enough me reckons - if you need more than that to sort out a speed change mid shot then I wouldn't like to be paying for all that stock ;)
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#9 Oliver Christoph Kochs

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Posted 11 January 2011 - 11:30 PM

You could always use the drive shaft for speed ramps. Easiest method is the little hand crank that plugs in it. Do care about compensation with the variable shutter. You can build your own ramp motor that does this (drive the whole camera). Switch your camera in the OFF position if you use it.
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#10 Chris Millar

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Posted 12 January 2011 - 01:34 AM

Or you could just move the speed knob from 24 to 18 and stop down 1/2

You can even do it yourself with the preset switar lenses

simple
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#11 K Borowski

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Posted 12 January 2011 - 09:14 AM

Reading the thread title, it is confusing, because you are changing the speed at which the film TRAVELS THROUGH the camera, not the film speed. Granted the term "film speed" is almost idiomatic, just like we talk about "lens speed."

But it is important to use correct usage, however illogical it may seem, to avoid confusing. When talking about this, you should say "camera speed" or "speed ramp," not "film speed."



I actually agree with Adrian here. . . it is easier to do in post, as 0.4 stops of change isn't likely to be something one can change to precisely coincide with the frame rate change. So, if it is done in-camera, you might notice a slight change in exposure, especially during the change itself.

There's no real harm that this will do to the camera though. The only piece of advice I have as to running Bolex cameras at variable framerates is to not run them any higher than 24fps without film in the camera. It will harm the camera's clockwork motor, similar to running a car at 100MPH (160) for no reason ;-)
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#12 Chris Millar

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Posted 12 January 2011 - 03:16 PM

So, if it is done in-camera, you might notice a slight change in exposure, especially during the change itself.


fix it in post :lol:
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#13 K Borowski

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Posted 12 January 2011 - 08:39 PM

I don't know if you are saying that as a joke or your response is facetious.


Since 99.9% of editing is done digitally anyway, and you are going from a higher to a lower framerate, there is absolutely no reason not to just slow it down in post. Even with optical printers, they were doing this stuff. They did a lot of fake slow-mo by frame doubling in "Soldier."

The only advantage I could think of in-camera is that it is cheaper on film stock, marginally, and once it's done, it's done. No extra cost in the editing suite. But the digital speed-up will be better quality wise.

It's an integral frame number too, so no problems there.



If you were using a control unit on a modern electronic 35mm Panavision or Arri, I'd advocate doing it in camera, but with a wind-up speed governed clockwork camera, it doesn't exactly change speeds on a dime either.
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#14 Chris Millar

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Posted 12 January 2011 - 10:36 PM

I don't know if you are saying that as a joke or your response is facetious.

Neither - but there was a small and clumsy irony - not sure where jokes turn inappropriate for you, so cant comment

Since 99.9% of editing is done digitally anyway, and you are going from a higher to a lower framerate, there is absolutely no reason not to just slow it down in post. Even with optical printers, they were doing this stuff. They did a lot of fake slow-mo by frame doubling in "Soldier."

Frame blending is one reason - either that or stuttering motion
If the rate change were higher then youd have a noticeable 'relative' shutter angle change also - prob not so much an issue here though.

The only advantage I could think of in-camera is that it is cheaper on film stock, marginally, and once it's done, it's done. No extra cost in the editing suite. But the digital speed-up will be better quality wise.

Not if its done properly in camera it wont

It's an integral frame number too, so no problems there.

Theres only one group of speed changes that wont result in frame blending and they factors of 2 slower - but then you've got that shutter angle change issue - and its all going to blend with the ramp anyway - to get from 24 to 18 you have to go through other frame rates between

If you were using a control unit on a modern electronic 35mm Panavision or Arri, I'd advocate doing it in camera, but with a wind-up speed governed clockwork camera, it doesn't exactly change speeds on a dime either.

It doesn't exactly keep speed in the first place! hence a bit of slop in a ramp will be within the mush of every other variable...

and its just fun -

I dunno - shoot both methods and see yeh ? :)
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