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Frame Speed changes on Bolex


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#1 Goodwill

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Posted 15 March 2006 - 12:52 PM

Hey guys,
So I shot some scenary stuff for my film with a bolex, and at the beginning of the roll, it seems like everything is going in fast motion. I shot at the lake, and hte water at the lake seems to be moving very fast, yet I know for a fact that I did not switch the frame speeds. I shot it at 24, but it seems like I shot it in 18, but then closer to the end of the roll, the footage begins to slow down a bit, does anyone know why this is? Thanks.

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#2 Jan Weis

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Posted 15 March 2006 - 04:23 PM

Hey guys,
So I shot some scenary stuff for my film with a bolex, and at the beginning of the roll, it seems like everything is going in fast motion. I shot at the lake, and hte water at the lake seems to be moving very fast, yet I know for a fact that I did not switch the frame speeds. I shot it at 24, but it seems like I shot it in 18, but then closer to the end of the roll, the footage begins to slow down a bit, does anyone know why this is? Thanks.

Goodwill


I'm not and expert when it comes to Bolex h16 cameras but I think the problem is that your Bolex is getting old. Clockwork cameras like bolex h16 dont shoot constant speed as well as cameras that go on batteries such as a Beaulieu r16(even though that camera doesnt go at sync speed). I bet if you get your bolex serviced itll run at a better constant speed..

Another alternative could be that your projector isnt working as well as it should be but I think that its highly unlikely.


Good luck
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#3 Boris Belay

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Posted 05 April 2006 - 05:50 PM

Hi, An easy way to check your camera speed (any camera, so long as it has a frame counter) is to load a dummy roll and check the number of frames against a stopwatch -- on a Bolex spring model, I check over 20 seconds to have a fairly reliable reading.
By the way, this is a good thing to do on H16's anyway since the 24 ips setting is not clearly indicated. And also, of course, the camera may have gotten a little slow over time.
I begin by setting the 18ips speed, because the dial does indicate 18ips precisely. It takes a good number of trials to get it precisely set : load the spool, wind the spring, reset the frame counter to 000, fire the camera and stop-watch at exactly the same time (mine, a common sports-style 3 button stopwatch, is conveniently laid out so that I can fire the camera's front release with the stopwatch's start button, so they're synchronized quite simply. I then hold the side release in running position and release it at exactly 20 (or 10) secs.)... then check the result, move the speed selector accordingly, and go on like that until it's good (enough).
When I have the camera running reliably at 18ips, I set the dial to the correct position (it is held by two tiny screws that can be loosened with a common jeweller's screwdriver). You have to be careful not to move the speed setting while matching the dial, obviously. Once it's set and re-tightened in the correct position (if need be), I then find the 24 ips (same time-consuming procedure) and mark it with a precise little mark engraved with the tip of a knife.
This is useful if you need a 25 ips setting on your H16 too.
For other models of camera without frame counters, you could use a length of film that has been cut to an exact number of frames (with an external film counter), allowing for the loop and loading length, obviously.
Remember that the longer you run your trial sample, the more accurate your reading : less variation due to a sloppy start/stop synchronization, errors in timing more obvious because multiplied by the time running and more precise time setting (1 frame off over a second is much worse than 1 frame off over 20 !), and a more accurate estimate of your motor's real-world accuracy over the time of actual scene shots.
B.
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#4 Nick Mulder

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Posted 17 June 2006 - 06:10 PM

all the bolexes I've tested so far will fun ~2 fps slower at the end of a spring wind than at the beginning - with this in mind the methods outlined will only ensure an average of the measured fps ...

you mentioned that the scene speed gets slower at the end of a roll as opposed to the end of a take - two weird things here... first if it were the spring it should get faster at the end... and in any case the sprocketed rollers rule out any possibility of the moment/lever arm of the take up and feeder spools changing the physics of the film transport through the gate...

perhaps near the end of the roll you kept the spring relatively more wound ie. a short take, wind and never letting it run down - yet at the beginning of the roll you were letting it run fully down ?

that way you could be shooting at 25 at the end and 23 at the beginning - an older un-lubed bolex may yield a larger discrepency in fps...
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#5 Hal Smith

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Posted 17 June 2006 - 07:06 PM

There's two variables involved in H16 speed constancy. My last Bolex had been used exclusively with a motor before me. The tech who worked on it commented that the speed was off because the governor was tired, but the spring was good as new and that was very unusual, to find an H16 with a really good spring.
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#6 Nick Mulder

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Posted 18 June 2006 - 06:54 AM

There's two variables involved in H16 speed constancy. My last Bolex had been used exclusively with a motor before me. The tech who worked on it commented that the speed was off because the governor was tired, but the spring was good as new and that was very unusual, to find an H16 with a really good spring.


how do governers get tired ? they are pretty simple mechanisms ... do you mean the governer springs get tired letting the weights fly out more (ie. slower speeds) ?
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#7 Hal Smith

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Posted 18 June 2006 - 10:30 AM

how do governers get tired ? they are pretty simple mechanisms ... do you mean the governer springs get tired letting the weights fly out more (ie. slower speeds) ?

I got that impression from talking to the tech - it becomes "too sensitive" was his description.
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#8 James Erd

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Posted 18 June 2006 - 11:02 AM

Hey guys,
So I shot some scenary stuff for my film with a bolex, and at the beginning of the roll, it seems like everything is going in fast motion. I shot at the lake, and hte water at the lake seems to be moving very fast, yet I know for a fact that I did not switch the frame speeds. I shot it at 24, but it seems like I shot it in 18, but then closer to the end of the roll, the footage begins to slow down a bit, does anyone know why this is? Thanks.

Goodwill


I'm wondering how long the camera has been sitting around since the last time it was used. The change in speed over the day may indicate that the lubrication in the clock works may is starting to dry up. A lot of old mechanical still cameras will behave erratically at first if they have been sitting for a long time, so many camera collectors exercise there collection on a regular basis.

A service would be a great idea, but you may find that just running the camera more often will do the trick, but don't run the mechanism faster than 18 fps with out film.
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#9 Nick Mulder

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Posted 18 June 2006 - 02:41 PM

I got that impression from talking to the tech - it becomes "too sensitive" was his description.


Once you see a governer and understand how it works (the physics behind it) its a simple and in my opinion very ingenious device. I decided to bite the bullet and pull my SB apart a few weeks back - I learned so much, would recommend it but only if you have a supply of spares ready, yet if you are careful you wont need them...

they are hard little buggers to describe in words hence phrases like 'too sensitive' which is a ??? for me are perhaps as appropriate as we should expect :lol:

A service would be a great idea, but you may find that just running the camera more often will do the trick, but don't run the mechanism faster than 18 fps with out film.


what is it that actually wears when you run a bolex without film at the faster speeds ?
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#10 Clive Tobin

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Posted 19 June 2006 - 10:31 PM

what is it that actually wears when you run a bolex without film at the faster speeds ?


The governor pads spin very fast. Without the load of pulling film through the gate, and the drag of the takeup spool, all of the spring power goes to the governor to "use up" which can make it wear out or overheat. As I understand it.
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#11 Nick Mulder

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Posted 20 June 2006 - 03:22 AM

The governor pads spin very fast. Without the load of pulling film through the gate, and the drag of the takeup spool, all of the spring power goes to the governor to "use up" which can make it wear out or overheat. As I understand it.



overheat ? :huh: interesting... I might need another look at one in action, seems I'm missing some understanding
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