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Bolex Timelapse - Correct Exposure on manual?


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#1 Gautam Valluri

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Posted 09 July 2015 - 07:36 AM

Hi Guys,

 

I'm planning to do a time-lapse on a spring wound Bolex H16. I will be shooting Kodak 500T 7219, around twilight on a busy street in London with lots of street lights, neon sigs etc. I will be using only a tripod and will not be able to use any additional lights. I do not have an interval meter so I will have to do the time-lapse manually using the single-frame option. I plan to expose every 3-4 seconds.

 

The lens will be the prime lens that comes with the Bolex (sorry, I need to check the focal length on this one and come back to you guys).

 

My questions:

1. What can I do to get a decent exposure?

2. How do I get a proper light reading?

3. What else do I need to keep in mind regarding time-lapsing by hand, the 7219 stock and shooting on london streets in general?

 

Any pointers will be much appreciated.

 

G

 

 


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#2 Carl Looper

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Posted 22 July 2015 - 03:12 AM

You'll need to use a light meter.

 

If using a reflex Bolex, then you'll need to take into account the prism which diverts 20% of the incoming light to the reflex viewfinder.

 

To compensate for this light lost to the viewfinder the easiest way to do that is to set the ASA on your light meter to 80% of the film's rated ASA. For example, if using 500 ASA filmstock, then 80% of this would be 400 ASA. The nearest ASA number on your light meter will be 400 ASA. So set the light meter to 400 ASA.

 

Next you want to set the exposure time on your light meter. If you are exposing frames manually, ie. by holding the shutter open for x seconds then just set the exposure time on your light meter to the number of seconds you are holding the shutter open.

 

However 500 ASA is quite a fast stock. You may not need to do manual exposure. Could try setting rate at 9, 12 or 24 fps and take single frames.

 

If you using a frame rate rather than manual exposure time, the exposure time per frame will be:

 

   shutterAngle / ( frameRate x 360).

 

The Bolex shutter angle is 135 degrees. So, for example, if shooting at 9 fps, then the exposure time will be 135 / ( 9 x 360)  = 0.0416 secs = 1/24th sec

 

Other exposure times can be obtained in similar fashion:

 

12 fps: 135 / (12 x 360) = 0.03125 secs = 1/32nd sec

24 fps: 135 / (24 x 360) = 0.015625 secs = 1/64th sec

 

Take a light meter reading and set the camera iris (or 'aperture' as I tend to call it) according to the meter's recommendation.

 

C


Edited by Carl Looper, 22 July 2015 - 03:25 AM.

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#3 Rolla Tahir

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Posted 28 July 2015 - 11:14 PM

I'm using the Bolex H16 and Tobin intervalometer to shoot dusk timelapse with 500T Kodak stock. I have a couple of questions:

 

- In 'Normal Exposure' and using a 5 stop down filter, do I still adjust my light meter to 400ASA?

- How do I expose for both dusk and into night (only lit by moon light)?

- You mentioned setting the expsoure time on the light meter, what do you mean by that? I'm using the analogue sekonic light meter.

 

The math of it all is quite confusing if anyone here has a good resource I can look into, it'll be much appreciated!


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#4 Simon Wyss

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Posted 29 July 2015 - 02:44 AM

You first need to know what camera model you’re using because there are differences among various shutter designs, early standard and reflex viewfinder cameras. Models from 1935 to 1954 have an effective shutter opening angle of 190 degrees. From serial number 100,401 on you have a 170 degrees shutter. The reflex viewfinder models have a 156 degrees shutter, the reflex variable-shutter models have 144 degrees full open angle. The reflex prism deflects between 20 and 25 percent of the light according to focal length (less at shorter focal lengths).

 

It also makes a difference whether you expose by the spring drive or by electric motor.

 

The math isn’t that complicated. Calculate exposure time as Carl indicates. Paillard gives 1/40 sec for single-frame exposure. For best results the actual state of the mechanism and spring torque should be determined by a test strip. Set the speed dial to 32 fps or higher.


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