Shooting a short film tomorrow, some questions

[brandon kaufman]

Hello!

Hope everyone's doing well. I'm shooting a little thing with my Bolex tomorrow without a DP. (It's mostly just for fun because I haven't been doing much since Covid started). With that said, I have some questions. You'll have to excuse my technical incompetence. The camera is an H16 Reflex (it says 176944 on the bottom) and the leens is a Switar 25mm (no. 506204).

1. I've read that the variable shutter reduces the need for a neutral density filter. When I'm metering a shot how do I adjust for this? I'm mostly shooting outside, so I would likely need to stop down, correct? I have a Sekonic L-398.

2. I've got two No. 1A Skylight gel filters, which supposedly make outdoor shooting warmer and cool blues. Would you recommend using this? Would I need to adjust my shooting in any way? I have the attendant adapted shutter speed numbers for 24fps (normal: 1/80 - 1/2: 112 - 1: 188) but to be honest I'm not sure how I need to readjust.

3. Given my lens (which I'm not sure adjusts for the lost reflex light), would I have to take into consideration the effective 1/80 shutter speed? Or does the lens negate this?

I really, really appreciate everyone's help + time.

All the very best, and let me know if you need any more information.

[Tyler Purcell]

Here is a good breakdown of the Bolex H16, which includes details on the variable shutter and how it works. 

https://helpwiki.evergreen.edu/wiki/index.php/APS_Bolex_16mm_Reflex_Operating_Guide

Lenses are lenses, there are no special lenses that compensate. The beam splitter Bolex like the H16R, has a 1/80th "effective" shutter speed, that number includes the beam splitter light loss. It's around 1/3 to 1/2 a stop difference. 

No reason to filter unless you're using super sensitive stock, which would be the wrong stock for shooting outdoors anyway. 

[Dom Jaeger]

42 minutes ago, Tyler Purcell said:

Here is a good breakdown of the Bolex H16, which includes details on the variable shutter and how it works. 

https://helpwiki.evergreen.edu/wiki/index.php/APS_Bolex_16mm_Reflex_Operating_Guide

Lenses are lenses, there are no special lenses that compensate. The beam splitter Bolex like the H16R, has a 1/80th "effective" shutter speed, that number includes the beam splitter light loss. It's around 1/3 to 1/2 a stop difference. 

Unfortunately that Evergreen College manual is spreading the misinformation that RX lenses do compensate for the prism light loss. The bolexh16user site says the same, and it seems to be a very common misperception. I've emailed them but I never get a response.

I don't know where these people get the idea from, it's not in any official Bolex literature. And anyone who is literate with lens terminology knows that an f stop (which is what RX lenses like Switars are marked in) cannot be adjusted to let more light in. An f stop is a fixed mathematical relationship between focal length and entrance pupil. Some cinematography lenses are marked in T stops, which are f stops adjusted for the internal light loss that occurs within a lens, but never for an external factor like a reflex prism. 

The only things an RX lens compensates for are the optical aberrations introduced by having a block of glass in the light path. They do not compensate for the prism light loss.

The fact that RX lenses were only made up to 50mm ( because longer lenses don't exhibit the aberrations as much as wider ones) should be a clue that light loss is not compensated for. The light loss occurs no matter the focal length, so why would Bolex not make RX lenses for all focal lengths? If you had say a Switar 25mm RX and a  Switar 75mm (no RX made) you would have the crazy scenario of having to change your metering every time you swapped between lenses.

 

4 hours ago, brandon kaufman said:

1. I've read that the variable shutter reduces the need for a neutral density filter. When I'm metering a shot how do I adjust for this? I'm mostly shooting outside, so I would likely need to stop down, correct? I have a Sekonic L-398.

The variable shutter has half and full stop reduction settings (marked 1/2 and 1) so if you needed to reduce more than a stop of light you would still need ND filters. The manual has adjusted exposure times for the variable shutter settings which you can enter into yr meter.