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True 24fps on the motor


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#1 Bryce Lansing

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Posted 30 September 2009 - 11:38 AM

I got my Bolex used on ebay, in great condition. I took it to a friend of mine who knows a great deal about Bolexes, and he said it was working great. But he pointed out on the motor, a little notch scratched in right before 24. He suggested that the previous owner probably marked that as the true 24fps. I shot a test roll, but I forgot to try both. I only shot it at that notch. I'm sending it out of state for telecine, so I wont be able to see for a while.

Is it common for true 24fps to be not quite over the number 24? Or is it always supposed to be right on the 24?

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Edited by Bryce Lansing, 30 September 2009 - 11:39 AM.

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#2 Bernie O'Doherty

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Posted 30 September 2009 - 03:13 PM

An easy way to check speed is to use the frame counter. Put a dummy roll of film in the camera, since this ensures the true running speed. Set the frame counter to zero. In ten seconds you should register 240 frames.
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#3 Chris Millar

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Posted 01 October 2009 - 06:28 AM

There is no 'true' 24fps on a Bolex without a crystal sync motor ...

Even if you find 24fps within a given tolerance Bolex motors tend to run fast at the beginning of a wind compared to the end, especially older Bolexes (i.e. %95 of them).

Yes, that mark is likely there as at some stage that was found to be acceptably 24fps for whoever was using the camera at the time, as for its accuracy now, you'll have to test it as Bernie suggests ;)

Another way is to stick a digital multi meter probe on the 1:1 shaft - even with out grounding it and having a potential difference for it to read many DMM's in frequency mode will pick up the smallest variation in charge and therefore give you a Hz ... Tricky to describe, and fraught with dodgy technique - buy hey! all I'll say is that is has worked for me ... :lol:
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#4 Bryce Lansing

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Posted 01 October 2009 - 10:44 PM

I'm not sure how accurate my start and stop of the stopwatch was to the start and stop of the motor, but at 24, I usually get between 248-250 frames (which is 24.8fps or 25fps right?). At the Mark, usually got between 238-240 (23.98fps is what digital 24p is isn't it?)

Chris, you make a good point about the slow down at the end. If I were shooting a shot longer than 20 seconds, would I be better off shooting at the 24 (giving me about 25fps), so that when it runs down at the end, I at least wouldn't be getting less than 24fps?

Is there a very noticeable difference between 24fps and 23fps?
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#5 Chris Keth

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Posted 02 October 2009 - 12:17 AM

I'm not sure how accurate my start and stop of the stopwatch was to the start and stop of the motor, but at 24, I usually get between 248-250 frames (which is 24.8fps or 25fps right?). At the Mark, usually got between 238-240 (23.98fps is what digital 24p is isn't it?)

Chris, you make a good point about the slow down at the end. If I were shooting a shot longer than 20 seconds, would I be better off shooting at the 24 (giving me about 25fps), so that when it runs down at the end, I at least wouldn't be getting less than 24fps?

Is there a very noticeable difference between 24fps and 23fps?


You wouldn't really notice a difference.
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#6 zhuo chun bei

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Posted 07 October 2009 - 11:58 PM

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#7 Guy Bodart

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Posted 30 November 2009 - 10:12 PM

I got my Bolex used on ebay, in great condition. I took it to a friend of mine who knows a great deal about Bolexes, and he said it was working great. But he pointed out on the motor, a little notch scratched in right before 24. He suggested that the previous owner probably marked that as the true 24fps. I shot a test roll, but I forgot to try both. I only shot it at that notch. I'm sending it out of state for telecine, so I wont be able to see for a while.

Is it common for true 24fps to be not quite over the number 24? Or is it always supposed to be right on the 24?

Posted Image


As I can see on the picture, your camera needs to be lubricated and the governor must be replaced.
The 24fps must be on the 24 marking and the camera must run 27 secondes. Using the frame counter or a piece of film(Marked every 24frs) and a chronometer will tell you the speed of the camera. But NO ONE BOLEX runs at the real 24frs.Or you need a crystal motor. So, any Bolex run at + - 24 frs...But it's not a real 24frs to sync.
Cameraspro
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#8 Chris Millar

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Posted 01 December 2009 - 01:46 AM

As I can see on the picture, your camera needs to be lubricated and the governor must be replaced.
The 24fps must be on the 24 marking and the camera must run 27 secondes. Using the frame counter or a piece of film(Marked every 24frs) and a chronometer will tell you the speed of the camera. But NO ONE BOLEX runs at the real 24frs.Or you need a crystal motor. So, any Bolex run at + - 24 frs...But it's not a real 24frs to sync.
Cameraspro

Governor replaced ?? :blink:

What are we looking at on the picture that tells us that ?

And if you mean that the scratched mark - which we dont even know is intended to be a 24fps marking - isn't lined up with the '24 marking' (which begs the question where is the '24 marking' exactly anyway) - then why not just move the registration of the fps marking dial ?

Rustling up some work ?

Your method of counting the speed will only give you an average speed, it wont tell you anything about the change of speed over the full wind.
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