Jump to content

App or user-friendly way to measure exposure when shooting film


Recommended Posts

I recently got a Double-8 (not Super-8) Bolex C8 camera in near mint condition.

I mostly shoot Super-8 as far as small film gauge goes, but given the condition of the camera and how fun it looks to use, and also that I’ve never used this format, I thought I’d give it a go and get film and a good lens for it.

I got a really nice D-mount 1.4 Yashica lens for it, but now I’m wondering how to expose film properly, since the camera has no electronics or auto settings.

For still photography, I use iPhone lightmeters like Lux, and get really good results, but are there user-friendly ways to measure exposure settings for film, based on the chosen frame rate?

Edited by Fabrice Ducouret
Link to comment
Share on other sites

  • Premium Member

You can use the exact same methods for exposing still film and movie film. The only difference is that the shutter speed in movie cameras depends on the frame rate. The shutter in a movie camera is usually a continually spinning rotating disk with some portion cut out of it. A rotating shutter with exactly 1/2 of the circle missing is referred to as a 180 degree shutter (out of 360 degrees). So the effective shutter speed at 24fps is 1/48 second. 

However, with Super 8 and some cheaper 16mm cameras, they may have a different shutter angle, or even a guillotine shutter. A lot of Bolexes had a variable shutter angle, but if I recall correctly the maximum angle was often below 180, more like 150 or 135 degrees. I would do some research and try to find out what the shutter angle of your Bolex actually is. 

Also, there will also be some light loss from these cheaper cameras that have a beamsplitter reflex viewfinder, as a portion of the light gets diverted before hitting the film and goes to the viewfinder optical path. So you’ll want to find out what that light loss is, if any, and factor that into your exposure calculations. Usually, it’ll be something simple like subtracting 1/2 or 2/3 stop from the meter reading.

Link to comment
Share on other sites

  • Premium Member

The simple C 8 have 170 degrees shutter opening angle, the variable-shutter models have 135 degrees. Exposure time is mathematically [(360°/170°) × number of fps]–1

or 2.12 × 16 = 34, 1/34th of a second. These pocket cameras don’t have prisms in the light path.

To adjust speed first load camera with dummy film, put a mark on it, place mark behind aperture, wind spring fully, and let it run down completely. Mark film at aperture, remove film, and count number of perforation holes between marks. One foot of Double-Eight film contains 80 hole pairs. Now turn speed dial run after run until that length is transported in the corresponding time like, say, 496 frames in 31 seconds. If you wish to be sure about perfect functioning of camera, an overhaul won’t be wrong.

Edited by Simon Wyss
typo
  • Upvote 2
Link to comment
Share on other sites

  • Premium Member

Here's a manual for the Bolex C8, worth reading first:

http://www.vintagecameras.fr/images/MonSite/BOLEX/C8/_Doc/Bolex_C8_Manual_en.pdf

The exposure times are actually written on the side of the camera, 1/35 sec for the standard speed of 16 fps. That works out to be a 165 degree shutter, though it may be 170 degrees as Simon says and the speeds were just rounded off.

You could probably use any lightmeter with a 180 degree cine mode set to 16 fps and it wouldn't be far off - 1/32 sec compared to 1/35 sec is a small fraction of a stop - there's probably more error in the lens aperture ring, and if the lens is marked in f stops as most D mounts are you probably want to open up a 1/4 stop more to compensate for internal light loss anyway. There's no reflex prism or anything else to divert light though. A small error in the running speed won't affect your exposure much either, but it will make human motion look a bit off.

I use an old selenium lightmeter (no battery) for shooting standard 8 and it seems to work fine. It came with a camera I bought and must be 60 years old, but others I've used have degraded a bit and lost sensitivity in low light. 

If you ever feel inclined to lubricate your camera, those little Bolexes are easy to open up and service. Here's a basic guide I wrote a few years back (it's for the more advanced D8L with triple turret and variable shutter, but the internal mechanism is more or less identical):

http://cinetinker.blogspot.com/2013/01/servicing-bolex-d8l.html

  • Upvote 2
Link to comment
Share on other sites

  • Premium Member

Paillard-Bolex B 8, no. 419233, 165 degrees. It’s getting weirder and weirder. I shouldn’t have presumed anything like that.

P1010977.thumb.JPG.26dd5bcc3c810674c56c2bcaae5e2f32.JPG

If we do some calculation with the table on the cameras, we come to three different angles (see the formula in my former post): 164.6°, 172.8°, 169.4°. Obviously, the exposure time values are rounded.

Of course these are mathematical figures. In practice we have to reckon also with speed variations and other factors.

 

Edited by Simon Wyss
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...