(Another) thread about exposure.

Brenton Lee · April 29, 2016

Hey people. I know it's a topic that's done to death but there's just so much information out there that it's easy to get lost in it so I'd like some other peoples opinions.

I've been shooting on a Bolex EBM (converted to S16) for a little while and have been getting "okay" results. Having a background in 35mm still photography was helpful but it's taking me a while to understand fully how to set the camera/lens up to expose the film correctly. And judging by other peoples footage on youtube, it's something a lot of people don't fully understand.

I have been working with the following factors which I pulled from an old Bolex manual (feel free to jump in and correct me, as it may help with the inconsistencies I get in my footage):

The shutter angle is fixed at 170 degrees.

At 24 fps, this gives me 1/50th exposure time but because of light lost through the viewfinder mechanism, its more like 1/67th.

So I would get my light meter out, set the ISO at 200, set the shutter speed at the closest speed (on this one it's T = 60) and take a measurement. Say it would give me an F of 2.8. I'd set the aperture on the lens and start filming.

For the most part this worked out okay, especially in well lit conditions. However, for any other condition it was very variable.

Am I doing this correctly? Is there anything different I should be doing?

And once I start getting measurements outside of my set ups capabilities (I only have an Angenieux 12-120 lens right now) is it just a matter of moving to a higher / lower speed film, higher speed lenses, incorporating ND filters, etc?

Anyway, thank you for reading this - feel free to contribute anything you like. I'm sure other beginners would appreciate it as much as I would.

Brenton.

Tyler Purcell · April 30, 2016

Generally, you want to meter the bolex at 1/80th of a second.

If your meter only goes to 1/60th of a second, then run half a stop more open to compensate.

Dom Jaeger · April 30, 2016

1/80 sec is the recommended "adapted" exposure time at 24fps (taking prism loss into account) for most reflex H16 Bolexes, which have 133 degree shutters. But for EBM and EL cameras which have a 170 degree shutter, the "adapted" exposure time is 1/67 sec, as Brenton said.

It's probably better to overexpose a tad rather than underexpose, so if your meter only has a 1/60 setting, maybe open the aperture up another third of a stop.

The other thing to remember is that all lenses lose a bit of light through internal reflections, primes usually a third of a stop or less, older zooms maybe a half stop or more. If a lens has T stop marks (which have compensated for internal light loss) you can use those, otherwise open the lens up a little more than the f/ stop reading.

It's also important to know how to meter a scene properly, lots of threads in the archives of this site on that topic.

Brenton Lee · April 30, 2016

Thanks so much for the feedback, it's good to know I wasn't doing anything completely wrong and that I just gotta fine-tune my approach a bit more.

I have another question.

If I was to start filming with an SR3 (Advanced), is there any similar light loss I need to take in to account? Whilst I somewhat understand the internals of the Bolex, I haven't really looked at how the SR3 works. I would be shooting with the shutter at 180 degrees.